crimson156
Rough_Rock
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how much does Fluorescence affect diamond quality
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"Quality" ? you mean price... With the kind of price variation in dimaonds, it is not easy to tell: around 5% discount would probably make sense.
Yeah, unusually strong flourescence may look hazy, but examples of that phenomenon are vanishingly rare (some GIA study mention somewhere on pricescope placed this probability way below 1% of diamonds sold). What you are more likely to see is a change in color depending on the UV component of the prevailing lighting, but this is not visible in diamonds with already high color grades: those appear to take up some blue-ish component in their flash, and some explain the mith of the "blue-white" diamonds by referring to this impression of fluorescence in high whites. A yellowish diamond (say O-P or lower) with strong fluorescence would change color outright from yellow to brownish (or something tea-like) instead.
Yeah, unusually strong flourescence may look hazy, but examples of that phenomenon are vanishingly rare (some GIA study mention somewhere on pricescope placed this probability way below 1% of diamonds sold). What you are more likely to see is a change in color depending on the UV component of the prevailing lighting, but this is not visible in diamonds with already high color grades: those appear to take up some blue-ish component in their flash, and some explain the mith of the "blue-white" diamonds by referring to this impression of fluorescence in high whites. A yellowish diamond (say O-P or lower) with strong fluorescence would change color outright from yellow to brownish (or something tea-like) instead.
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mike04456
Brilliant_Rock
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The "fluorescence is always bad" theory is a myth that has been completely debunked, but many in the industry still believe it. In rare cases, very strong fluorescene will cause a milky appearance, but it's far more common for medium-strong fluorescence to make a yellowish diamond look whiter. I have a channel-set ring with six little diamonds, one of which has strong yellow fluorescence, and I cannot tell the difference between that one and the other five except under a UV lamp.
Kay
Ideal_Rock
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On 1/19/2004 2:24:52 AM Cut Nut wrote:
I prefer fluoro diamonds and the fact they are less costly is one of the wierdest glitches in life----------------
I love that particular glitch. I have a D with blue fluorescence -- I love the look of it, and it was such a bonus that the fluor actually reduced the price.
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Here are some articles I would one day like to edit and summarise - it's a bit of a hotch botch.
Is Blue Fluorescence Bad News? Not Necessarily,
Says GIA Study
Here are some extracts of the study “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds,” (1997) in the GIA journal that was reported in Rapaport Diamond Review in
For a number of years, the strength and color of fluorescence in a diamond have been singled out by many in the trade as an important characteristic of that diamond. Often the presence of moderate to strong blue fluorescence is applied across the board as a marker of lower offering prices, based on a belief that such fluorescence has an undesirable effect on the color appearance and transparency of a polished diamond.
At the same time, others in the trade have contended that overall appearance typically is not negatively affected by fluorescence. Before this study, however, there had not been any controlled investigation of this subject. To address this situation , GIA and GIA Gem Trade Laboratory researchers designed a visual experiment as a first step toward understanding how and what conditions fluorescence affects a diamond’s color appearance or transparency.
The purpose of this study was to explore the perceived influence of reported blue fluorescence in colorless to faint yellow diamonds when they were viewed in different positions and under different lighting conditions by observers from both within and outside the diamond industry.
Types of Diamonds Studied
Only about 35 percent of gem diamonds show any fluorescence, and of these, blue is by far the most common fluorescence color observed. A search the Gem Trade Laboraatory’s database from a recent time period showed that in 97 percent of those diamonds for which a fluorescence color was reported, that color was blue. Therefore, even though yellow fluorescence is also a concern in the industry, it is quite rare, so we decided to limit this study to blue fluorescence.
Four sets of six diamonds each were selected for the study. The six diamonds in each set had the same color grade, with the four color grades representing important commercial breakpoints: E, G, I, and K. All 24 diamonds were round brilliants, had good or better polish and symmetry, and were cut to similar proportions; most had clarities at or above the VS range. Since all these aspects of diamonds can cause differences in appearance, we tried to control them as completely as possible, leaving fluorescence as the one variable to be studied within each color set.
The diamonds in each set exhibited a range of fluorescence strengths that were typical of those most commonly encountered in the trade (see figure 1). Diamonds of extremely strong blue fluorescence, known as “overblues,” were not part of this study. Such diamonds have a noticeable oily or hazy appearance when excited by any of a number of light sources. Although diamonds described as very strong blue are routinely seen in the trade, a true “overblue” is rare.
Results of the Study
For the observers in this study, blue fluorescence had, at best, a subtle effect on color appearance and transparency. The non-trade observers made no consistent, meaningful distinctions of either color or transparency that related to fluorescence. Most of the experienced observers saw differences in color appearance, but less than half saw any differences in transparency.
Although we found some statistical correlation between color appearance and fluorescence, the responses varied from stone to stone, with some highly fluorescent diamonds in a color set singled out, while others of like strength in the same set were not. This inconsistency implies that other factors besides fluorescence affect color appearance for these different lighting and viewing conditions.
In the table-up position, diamonds described as strongly or very strongly fluorescent were, on average, reported to have a better color appearance than less fluorescent diamonds. There was a slight tendency for blue-fluorescent diamonds to appear less transparent table down in artificial light, but slightly more transparent when viewed table-up under sunlight.
There were also variations in perceived fluorescence effects for the different color sets. The effect on diamond color appearance was most noticeable in the lower colors (I and K), although in the marketplace the influence on price is greater in the higher colors (E and G). This study challenges the industry notion that fluorescence usually has a negative effect on better-color diamonds. GIA’s results show that the industry would be better served by considering each individual diamond on its own visual merits.
Blue White: a Brief History of Fluorescence
Posted: 4/9/1998
Extracts of an article by Martin Rapaport in the Rapaport Diamond Report April 1998
Once upon a time before the diamond industry standardized to GIA colour grading terminology the term Blue White (Blauweiss) was used to describe the finest colour white diamonds. The original Blue White diamonds came from South Africa's Jagersfontein mine. The best Jager stones were highly transparent (clear and colorless) with a bluish tint due to fluorescence. Ironically, during the early part of the 20th century fluorescence was seen as something that had a very positive impact on top colors. The extra sparkle fluorescence provided when the diamond was seen face up in sunlight was accepted as verification of the diamonds high color. Blue White diamonds were avidly sought out by the trade and consumers who paid higher prices for diamonds with fluorescence. Contrary to current market conditions, fluorescence added value to high color diamonds.
Now the history of what happened to fluorescence is very interesting and informative. The trade had something very good going with fluorescent Blue White diamonds, but they blew it. Instead of maintaining consumer confidence in Blue White the trade began selling all types of lower color diamonds as Blue White. The term Blue White and the underlying concept that blue (i.e. fluorescence) added value to white (colorless) diamonds was so abused by the trade that in 1938 the U.S. Federal Trade Commission outlawed the use of the term Blue White for anything but blue diamonds.
Abuse of the term Blue White and the subsequent FTC restrictions undoubtedly encouraged the establishment of GIA color grading system. Color grading systems try their best to differentiate between the amount of color or tint in a diamond (i.e. the degree of its transparency or lack of any color) and the sparkle effect provided by fluorescence (fluor) in various lighting environments. In fact, one primary reason the GIA developed standardized color grading using a Diamondlite box with a controlled light source was to be able to color grade diamonds while minimizing the
influence of fluor.
The bottom line is that blue fluor enhances the color of diamonds in almost all lighting conditions. Is this bad? If not, why does the trade pay lower prices for fluor diamonds?
In some instances the trade does pay more for fluor. Typically J color and lower fluor stones bring a better price. This is because they look whiter to the trade. However, when it comes to higher D-F colors in VS and better clarity grades fluor is discounted. In general the more expensive the diamond the greater discount.
Some people believe that the trade is making a mistake and fluor diamonds are wrongly discounted due to misinformation and a misguided herd instinct. The theory is that the trade misunderstands the impact of fluor on higher color stones which is minimal because there is very little yellow color in the stone to improve upon. Suppliers believe that if they could convince buyers not to discount fluor they would make more money and improve liquidity.
The GIA has just published a research report on the effect of blue fluor on the appearance of diamonds. Interestingly the GIA concludes, "This study challenges the industry notion that fluor usually has a negative effect on better color diamonds."
The GIA is saying that lower prices for high color fluor stones do not make sense. So why does the trade discount higher color fluor diamonds? Are the diamond markets irrational?
This writer tends to believe in the rational market theory. In other words, over the medium and long term markets are never wrong because prices reflect the combined wisdom of everyone everywhere. The old market rule, "You can fool some of the people some of the time and the rest of the people the rest of the time, but you can't fool all the people all the time," makes perfect sense. It is especially true when people are voting with their money. While education and information certainly shape demand, add value and influence market forces that set prices, over the long term, by definition, markets do not make mistakes, they value things correctly.
So why does the trade discount fluor? Let's view the market from the perspective of a diamond trader and consider some recent diamond history.
As the investment diamond boom developed in the mid 70's and prices for D-IF's skyrocketed, very strong blue over-white or over-blue hazy diamonds needed to be weeded out of distribution. Since traders were flipping certs over telex machines the easiest way to do this was by avoiding strong blues (SB). Sure some SB's were fine but you had to look at them and convince your customer they were ok. In some instances fine jewelers resisting mixing fluor goods with non-fluor goods because the stones face up differently. Also, the French who were important buyers at the time hated fluor. This may be because fluor means 'false color' in French.
Perhaps if certs didn't mention fluor no one would have cared about it. However, since it was there on the paper dealers figured they could use it to haggle and do some price differentiation. In soft markets dealers could discount fluor stones without disturbing the market value of inventory too much.
Traders were and still are disturbed by the correlation between over-graded colors and fluor. Nothing upsets a trader more than buying a G and finding out the stone is really an H because some lab made a mistake. Unfortunately, the probability of a lab over-grading a fluor stone is much greater than a non-fluor stone and a large percentage of high color mistakes turn out to be fluor. Over time mistakes pile up in the market since no one wants to buy them. This reinforces the notion that over graded stones have fluor. Perhaps if the labs graded fluor more conservatively dealers wouldn't be so afraid of them.
Korea’s scandal also had a great impact on world prices for fluor goods. See our June 1993 article "The Korean Blues" for full details. In short, the Korean labs over-graded the color of fluor stones which encouraged huge imports of fluor stones. In the early 90’s Koreans were the worlds largest buyers of fluor stones and as much as 50 percent of the stones sold in Korea were fluor. The bubble burst in 1993 when an investigative TV special informed Korean consumers that their fluor stones were over-graded. Korean consumers found out their G's were really H's and no one in Korea ever trusted a fluor stone again. Not only did the Korean buyers stop buying fluor stones they became net sellers as consumers insisted sellers replace the fluor stones.
As the market struggled to deal with the Korean problem along came the Russians dumping diamonds. Guess what? A huge percentage of Russia's diamonds were fluor. Now it is very nice for the cutters and the GIA to explain to everyone that fluor stones are OK (assuming they are not over-graded). But let's consider supply and demand from the dealers perspective.
I'm a dealer looking for D-F, IF-VVS goods. Expensive stones. 70 percent of the stones offered to me are fluor 30 percent are not. If prices are the same or near same, which stones do you think I am going to buy? Frankly, I don’t care what anyone says about fluor or even what the stones look like. I trade scarcity. I trade liquidity.
One primary reason dealers discounted fluor stones was to protect the market from the great inflow of Russian goods. The overriding factor justifying the market discount for fluor was scarcity. If D’s were expensive because they were rare it was reasonable to expect that scarcer D’s (i.e. D’s without fluor.) would be even more expensive. The trade did not and does not necessarily price diamonds based only on appearance. Scarcity also has a great influence on price.
Obviously from the market perspective there appears to be a reasonable basis for price discrimination against fluor. While this article supports the rational markets theory it is important that we pay careful attention to what the GIA is saying. It may very well be that the trade is over-discounting fluor. If fluor diamonds are graded accurately under ideal laboratory lighting conditions blue fluor. stones have an advantage in that their color improves in normal daylight.
While education can play an important role changing buyers perception about the negative impact fluor has on higher color diamonds it will have to backed up by solid results. In other words the labs are going to have to be very serious about not over-grading the color of fluor stones even though these stones tend to appear whiter than they are. Furthermore the labs must clearly indicate on their grading reports instances where milky fluor detracts from the quality of the diamond. Only then will the trade and consumers have the confidence to pay better prices for fluor stones.
Regarding relative scarcity, based on the GIA research fluor stones are scarcer than non-fluor stones. The reason the availability of fluor stones is greater in the market is because they are more difficult to sell. Over the long term if the trade changes its perception about fluor goods and they sell through on a more liquid basis market availability may decline so that there is no longer an oversupply of fluor stones in the market.
From an economic perspective, there appears to be little benefit to the trade by increasing prices for fluor stones. It is likely that any price benefit will be absorbed by higher CSO prices for rough. Furthermore, the availability of fluor stones helps the market adjust to varying degrees of availability. When the availability of higher colors are tight, the discount for fluor drops as buyers more readily accept fluor because there are fewer alternatives available. On the other hand when goods are plentiful the fluor discount grows protecting prices for non-fluor goods. This assures less price volatility for higher colors.
In conclusion, the GIA report is interesting and important. To some degree the GIA can influence market behavior, encourage greater acceptance of high color fluor stones and ultimately shift the demand curve for fluor diamonds. However, it is important for us to recognize the sophisticated nature of price making forces in the free market and the role of the market in deciding what is and is not a better diamond through pricing. The beauty of the free market is that it is a real changing live world, open to all information, influences and opinions. Yet at the same time markets provide real numbers that reflect the consensus of all participants as to the real value of diamonds.
By Michael Cowing, MS, FGA, NJA © Copyright 1998 All rights reserved.
Gemological Institute of America, (GIA), recently published in their quarterly journal, "Gems & Gemology", 1 the results of a human experiment in the observation of diamonds with various amounts of blue fluorescence. The article was entitled "A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds". An introductory editorial by GIA’s president William Boyajian indicates that the study "challenges the perception held by many in the trade that UV fluorescence generally has a negative effect on the overall appearance of a diamond". He makes it clear that this is a false perception, which the GIA hopes this study will help to dispel. He says this study "should bring into question the trade’s lower "bid" prices for moderate to highly fluorescent diamonds in the better colors".
Historically, the GIA has been the principal source of information in the area of diamond color grading for gemologists, appraisers and the diamond trade, so this article will generate much discussion. Because of the GIA's stature and credibility with the trade and the buying public, this article will be quoted by many to improve the relative salability of diamonds with the property of medium or strong blue fluorescence indicated on their grading report.
To help disseminate the message of this study to the trade, an abbreviated version of this article was published in the April 1998 issue of the "Rapaport Diamond Report". In the same issue Martin Rapaport responded with a thoughtful article, entitled "Blue White" in response to the GIA study’s conclusions. In it he explained the trades historical handling of blue fluorescence in diamonds from a pricing and marketing perspective. He points out why the trade discounts fluorescence in the higher gem quality diamonds, and how it came about that fluorescence comments, indicated on a diamond grading report, became undesirable. He concludes: "Obviously from the market perspective there appears to be a reasonable basis for price discrimination against fluorescence". He acknowledges "If fluorescent diamonds are graded accurately under ideal laboratory lighting conditions blue fluorescent stones have an advantage in that their color improves in normal daylight". Finally, he admonishes that "changing buyers perception about the negative impact fluorescence has on higher color diamonds … will have to backed up by solid results. In other words the labs are going to have to be very serious about not over-grading the color of fluorescent stones even though these stones tend to appear whiter than they are".
As a gemologist and member of the diamond trade, the author has been involved with this issue since the early 80’s and would like to make a contribution by addressing the following questions, which both articles should raise in the minds of their readers:
Are the labs over-grading blue fluorescent diamonds? If so, why? How can the labs insure they are not over-grading blue fluorescent diamonds and convince the trade of this? What can be learned from this new study beyond Boyajian’s and Rapaport’s conclusions? These questions are examined in the historical context of what gemologists have learned and taught the diamond trade regarding fluorescence and diamond color grading over the last 30 or so years.
The majority of natural gem quality diamonds contain nitrogen as an impurity. Depending upon the amount of nitrogen and how it is distributed throughout the diamond, this impurity causes the slight tints of yellow to which the GIA assigns the letter color grades from D to Z. This type of diamond is categorized as Type Ia. For simplicity and because it covers most of the gem color white diamonds, the GIA and this discussion address mainly this Ia diamond type. However the principles discussed are extensible to the other categories. This same nitrogen impurity in the type Ia diamond, depending upon the percentage and distribution of nitrogen, may cause fluorescence of varying intensities of blue or bluish-white.
Fluorescence is the emission of visible light from a substance being stimulated by invisible, ultra violet, (UV), energy such as that contained in sunlight and indirect sunlight. Gemologists look for this property of fluorescence in diamonds and other gems by employing ultra violet lamps. These UV sources use either a high or low-pressure mercury vapor tube with a filter that removes visible light emitted by the tube. This leaves energy or radiation in the short and long wave UV wavelength range of 200 nm to 400 nm. The two highest energy wavelengths put out by these tubes are 366 nm, which is in the long wave UV range, and 254 nm, which is in the short wave UV range. These wavelengths are selectively filtered to produce long and short wave UV energy for testing fluorescence. Another popularly used source of long wave UV is a low-pressure mercury vapor tube that excites a special coating which then emits long wave UV. When a diamond with blue fluorescence is illuminated with invisible long wave UV energy from one of these lamps in an otherwise dark environment the diamond glows blue. Short wave UV energy also stimulates blue fluorescence, but to a much lesser extent, leaving long wave UV the dominant source that produces this effect.
The GIA Article makes the point that a group of two nitrogen atoms, the A aggregate, tends to quench fluorescence while a group of three nitrogen atoms, called the N3 center, produces blue fluorescence. Since a single diamond may contain varying amounts of these nitrogen defects, the result may be anything from no fluorescence to extremely strong blue fluorescence. The GIA says this confounds "the trade notion that nonfluorescent diamonds are more "pure" than those that fluoresce, since there are nitrogen- related centers that extinguish fluorescence as well as those that cause blue fluorescence." They are making the important point that blue fluorescence or lack thereof is a property of diamond, not an indicator of "purity", since a nonfluorescent diamond may often have a greater percentage of nitrogen impurity than one that is blue fluorescent.
The light yellow tints in a Type Ia diamond combine with the various amounts of blue fluorescence to give the diamond its perceived color. Gemologists and the trade define and refer to the diamond’s "true color" as that color that a diamond exhibits when viewed under illumination devoid of any UV energy that would excite fluorescence. Because all the light sources regularly used to view and grade diamonds contain some amount of long wave UV energy the "true color" of a strongly blue fluorescent diamond is never seen. What is seen is the perceived net color. This net color includes whatever amount of blue fluorescence is stimulated by the light source’s UV energy. To explore the perplexity of perceived color verses "true color", we need to discuss in detail how gemologists have historically measured and graded color in a diamond.
Of primary importance in diamond color grading is the illumination used to view the diamond during grading. Under what illumination should the diamond be viewed in order to properly grade diamond color?
There are three general types of illumination, which have been used in diamond color grading. The first is the various forms of natural daylight. The second is fluorescent lighting, and the third is the various incandescent, filament type, light bulbs from high intensity tungsten to quartz halogen. Each of these forms of illumination has their advantages and disadvantages for use in color grading. Historically, the best form of natural daylight for color grading was found to be northern daylight. Eric Bruton’s classic book from the 70’s, 2 defines northern daylight to be "daylight from a North-facing window in the Northern Hemisphere and from a South facing one in the Southern". Grading was typically done during the daylight hours when the sun was high enough in the sky to avoid the reddish tint in early morning and late afternoon light. The very slightly bluish-white northern daylight made an ideal illuminant to detect the slight tints of yellow typical in gem quality diamonds.
To further the understanding of the properties of this light, which made it desirable for color grading diamonds, it is useful to introduce the unifying concept of color temperature. The measure of temperature described here is degrees Kelvin (K). Degrees Kelvin is just degrees centigrade (C) plus 273, because absolute zero, to which Kelvin temperature is referenced, is -273C.
When a substance such as the tungsten filament in an incandescent light bulb is heated to sufficiently high temperatures it radiates energy over a whole spectrum of different wavelengths. The spectrum extends from the very long infra red waves, which produce the sensation of heat, thru the 750 nm to 400 nm waves which produce the sensation of color from red to orange, yellow, green, cyan, blue, violet and then on into the invisible ultra violet short wavelengths between 400 nm and 200 nm. The perceived color of this spectrum is a function of the balance or distribution of energy over the visible wavelengths. When the filament temperature reaches 1500K to 2500K the visible wavelengths combine to give a reddish tint to the illumination. As the filament is heated to 2800K to 3200K the yellowish- white light of incandescent bulbs is produced. The higher the temperature is raised as in quartz halogen bulbs, the less yellow and more neutral-white the emitted light becomes. Incandescent lights reach a practical temperature limit at about 3400K, but at a color temperature of 5500K to 6500K the balance of energy in the visible wavelengths tilts to the very slightly bluish-white of northern daylight.
Compare color grading under a yellowish-white, incandescent illumination of 3200K to grading under the 6500K, bluish-white, northern daylight. You will find, as did the early color graders, that slight tints of yellow are more easily observed in the complimentary very slightly bluish-white northern daylight than in the yellowish-white light of incandescent sources. Thus, the color temperature close to northern daylight of 5000K to 6500K became the standard for color grading diamonds.
However, natural, northern daylight has another property that complicates the diamond color-grading picture. It is rich in both long and short wave UV energy. This invisible UV part of the spectrum of daylight excites the blue fluorescence in diamonds having this property. Early on, it was recognized that the perceived color grade of typical gem quality diamonds was a combination of the faint yellowish tint in the diamond and any blue fluorescence caused by UV from the illuminating source. Since blue and yellow light are complimentary, they tend to cancel. A highly blue fluorescing, yellowish diamond will show its yellowish nature when viewed under illumination with a minimum of UV such as incandescent light, but will appear increasingly colorless in lighting with increasing amounts of long wave UV. Finally, in the UV rich illumination of daylight it may appear colorless or even slightly bluish-white. The plate glass windows, thru which the northern daylight enters, such as the floor to ceiling windows of the pictured, Antwerp diamond bourse, filter out most of the short wave UV energy. However, most all the long wave UV that is the main cause of fluorescence remains present.
This presented a real dilemma to early diamond graders including Shipley, the GIA’s founder. On the one hand the color temperature of northern daylight was ideal for color grading diamonds with slight tints of yellow, but at the same time daylight’s long wave UV energy was causing blue fluorescent diamonds to look whiter than they did when compared under incandescent illumination having a minimum of UV energy. Since the color of a fluorescent diamond changes as a function of the illumination under which it is observed, what should be the standard illumination to grade this color? Early on the GIA and others decided to separate the whitening effect of blue fluorescing diamonds from the basic yellowish tint by designing a standard light source with a close to northern daylight color balance of 5000K to 6500K, but unlike northern daylight having a minimum of UV.
The GIA Diamond Course from 1969, 3 stated "A large percentage of diamonds fluoresce, usually blue; and the fluorescence, if sufficiently intense will alter the color of such a stone when observed under a light source emitting ultraviolet rays. Since this occurs under daylight examination the most desirable conditions are to be encountered under a balanced artificial light with a minimum of ultra violet content." This is perhaps the most logical approach to the dilemma presented by fluorescence. By changing the standard illumination for color grading from northern daylight with a lot of UV to incandescent illumination with a minimum of UV, the color advantage that blue fluorescing diamonds possessed in daylight was minimized in the grading.
The GIA produced their first diamond color grading instrument, called the DiamondLite, using an incandescent filament type of light source and a "daylight filter" which produced "the equivalent of north light without the UV radiation." 4 At the same time the GIA Diamond Course stated that "a reasonably good substitute for the DiamondLite can be made by adapting a simple desk lamp fixture containing cool white fluorescent tubes." 5 However, they caution "the disadvantage of this kind of illumination is that fluorescent tubes emit a significant percentage of ultra violet radiation. Although this does not affect the grading of nonfluorescent stones, it causes fluorescent diamonds to be graded higher then is actually warranted due to the neutralizing, or masking, effect of the fluorescent color on the true body color." 6 Gemologists graduating from the GIA in the 1969 time frame came away with the principle that diamonds should be graded for color under a daylight balanced artificial illumination absent the UV radiation energy contained in natural northern daylight and also contained in fluorescent lighting. They learned that grading in daylight or fluorescent light with the attendant UV radiation will result in over grading a blue fluorescing diamond. This has become the conventional wisdom among gemologists since that time. Eric Bruton’s book, "Diamonds", published in the 70’s, indicated that gemologists worldwide shared these views on illumination for diamond color grading. In a section of his book under conditions for color grading, 7 he said a "very important consideration is that any fluorescence in the stone must be suppressed"…."It is therefore important to grade stones in white light that is relatively free of ultra-violet".
What has happened since that time? By the 70’s we find gemologists and the diamond trade worldwide are universally using some form of fluorescent light to grade color in diamonds. The later versions of the GIA DiamondLite have substituted Verilux brand, fluorescent tubes for the daylight corrected incandescent light source in the early model. This is the very same source of grading illumination that was said to result in the over grading of fluorescent diamonds. Does that mean that by their original color grading standards, gemologists are over grading blue fluorescent diamonds? If so, would that not make a good additional argument for discounting the "bid" price of blue fluorescent diamonds?
First of all there is indeed evidence to suggest that going by the original, UV free, diamond grading standards, the trade and anyone grading with fluorescent lighting is over grading diamonds with strong or very strong blue fluorescence and possibly even medium blue. This varies little, except in degree, from the over grading that many felt was occurring when natural northern daylight was being used for color grading. By using fluorescent lighting as the standard illumination for diamond color grading, gemologists have in effect redefined the standard amount of UV to be that contained in fluorescent lighting. Perhaps this is an acceptable alternative to grading in the absence of UV, but it presents its own set of problems. Most importantly, fluorescent illumination containing significant UV energy certainly does not reveal the "true color" as defined by the early gemologists and as understood by the trade. In addition, the amount of UV exciting the fluorescence in the diamond being graded varies with the tube’s manufacturer, with the tube’s age and with the distance the diamond is held from the tube during grading.
The new GIA article indicates that a digital radiometer was used to measure the UV content of each of the light sources that were used in the study. They found no appreciable differences in long wave UV content from one source of fluorescent lighting to the next including the Verilux tubes used in their standard DiamondLite. They also found "indirect daylight through our windows has about as much UV radiation as the fluorescent light sources". If fluorescent lighting and daylight have a similar amount of UV radiation as the GIA measured, it would be expected that blue fluorescing diamonds would be perceived to be relatively whiter in daylight and under the DiamondLite than they would be if no UV radiation were present.
The four, color sets of diamonds used in the GIA observation studies were carefully chosen from more than 1000 diamonds, so they would be similar to one another in all respects except their fluorescence. Of course, their colors were graded in the Verilux illumination of the DiamondLite, illumination that is the standard for grading diamond color at the GIA Gem Trade Labs. Excellent quality, color photos were published with the article of each of the four, six stone sets whose colors were E, G, I and K. These photos appear to provide an indication that at least some of these diamonds have been graded higher than they would have been under the old color corrected incandescent illumination of the first DiamondLites. Because the photos were taken in incandescent illumination, relatively free of UV energy, the blue fluorescing diamonds should loose most of their color advantage. Under incandescent illumination, comparing within a set of identical color grade should reveal the approximate, relative "true color" of these diamonds. For example, the I color set’s diamonds have measured fluorescence, from left to right, of: 1. Medium, 2. Very Strong, 3. Faint, 4.Strong, 5. None, and 6. Strong. If you study carefully those six stones in the face up photo, stones 2, 4 and 6 appear to have more color than the other three in spite of having been graded identically as I colors under the Verilux tube of the DiamondLite. It is more than a coincidence that these are the three with the strongest blue fluorescence, indicating that they have been overgraded relative to what they would have been had the illumination used for grading been the low UV, incandescent illumination used in the photo. The other sets are less consistent in showing this effect, but the highest fluorescing member of each of the E, G, and K color sets appears to be the most tinted of its respective color set. It is important to note that these differences in color appearance are not apparent in photos taken of the table-down view of these same diamonds, the view under which they were graded. If these same photographs were retaken using natural daylight with more UV than the Verilux tubes have, what would be the expected outcome? Using daylight film to take the photographs, you would find that the most yellow tinted diamonds, which were the most fluorescent members in each set, would now be the least tinted and might even appear bluish-white.
All this brings up another interesting problem for gemologists and anyone who uses colorimeters or spectrophotometers to assist them in diamond color grading. The GIA and many other organizations and manufacturers sell these instruments to assist the human eye in color grading diamonds. Colorimeters use incandescent light sources to make their measurements of color. Because of the differing UV content in incandescent vs. fluorescent lighting the colorimeter’s measurement of color in blue fluorescing diamonds will differ from the measurements the human eye makes under fluorescent lighting. This is a further dilemma for gemologists to ponder.
So we have come full circle. Thirty or more years later, we are again facing the question of whether the illumination under which diamonds are graded should contain long wave UV, and if so how much? We can stand pat with the GIA’s and the trade’s use of fluorescent light sources with their attendant somewhat variable amounts of UV as the de facto standard, and live with the fact that a blue fluorescent diamond will grade whiter due to the UV energy contained in this illumination. After all a blue fluorescent diamond does appear a whiter color in all but perhaps incandescent lighting. The result will likely be a continuation of the distrust of color grading done on blue fluorescent diamonds as discussed in Rapaport’s article.
There is an alternative course of action that is being taken recently by a number of gemologists and gem labs. They are adhering to the early gemologists’ teaching that the body color of the diamond should be graded in an illumination that is absent UV energy. They have found a simple, inexpensive method to filter out the UV energy from all light sources be they natural, fluorescent or incandescent. GE manufactures a window glass substitute called Lexan, which is a plastic that filters out virtually all long and short wave UV. By filtering the light thru a sheet of Lexan or other UV filter, all the three types of light sources used for color grading would be put on the same footing, namely no UV. This eliminates the possibility of the so-called over-grading of blue fluorescing diamonds due to UV. Of course it is even stricter a standard than the original DiamondLite since the tungsten filament light source it used still contained the minor amount of UV present in all incandescent lights. This solution to the problem should go a long way toward correcting the trade perception that labs are over-grading blue fluorescent diamonds. There would be much better correlation, when it comes to blue fluorescing diamonds, between colorimeter and spectrophotometer grading and human graders using fluorescent lights and natural lighting environments.
Whichever choice a gemologist or a member of the diamond trade makes, whether to continue using unfiltered fluorescent lighting or eliminate the UV energy by filtering, he should be aware of the impact of his decision on the color grading of blue fluorescent diamonds. Keep in mind that there are differing views about the degree to which the UV content in standard fluorescent lighting is affecting the grading of blue fluorescent diamonds compared to their nonfluorescent counterparts. While the GIA’s study concluded that "in general the results revealed that strongly blue fluorescent diamonds were perceived to have better color appearance when viewed table up" they found "no discernable trend table-down". Since this is the position used for color grading, perhaps, except for strong blue fluorescence, the grading is close to the "true color." A large number of gemologists and the trade appear to believe differently, and perhaps by filtering out the UV, these concerns can be allayed.
A final issue that both articles address is the perception held by most that blue fluorescence is sometimes associated with an attendant milky or hazy appearance. Rapaport admonishes "the labs must clearly indicate on their grading reports instances where milky fluorescence detracts from the quality of the diamond". At what point along the scale of fluorescent strength from faint to very strong blue can this milky appearance be noticed? Here again there is a difference in opinions. However, everyone acknowledges that this effect, which is a loss in transparency, has a significant negative impact on value and salability when it is present. This was a quality factor that the GIA study asked its participants to evaluate in order to make a contribution to answering this question. They did not include in the study "diamonds with extremely strong blue fluorescence and a distinctive oily or hazy appearance". In the range of fluorescent strengths, including very strong, the study found that "most observers did not detect any differences in transparency among diamonds in a given color set. Of those who did see a difference under fluorescent lighting, it was only apparent in the table-down position. These results challenge the notion that strongly fluorescent diamonds typically have a hazy appearance". The GIA believes that the study shows, up to and including strong blue fluorescent diamonds, there is no noticeable decrease in transparency in the normal face up viewing position. The study’s findings indicate that this may be one negative perception of blue fluorescent diamonds, harbored by the trade that may not be warranted except in the case of extremely strong blue fluorescence.
Concluding Remarks
The author encourages you to read or reread the GIA’s article and Rapaport’s response in the light of this discussion. Two possible simplified conclusions may be reached as to the correct direction the gemological community and the trade should take. They both have merit.
The first direction is to pursue measuring the "true body color" and minimize the fact that most diamond viewing environments enhance the whiteness of blue fluorescing diamonds because they contain significant amounts of UV energy. The grading labs and the trade could implement, using Lexan or other UV filters, a color grading environment absent UV in order to grade the "true body color" as taught by the early GIA Diamond Course. If all color-grading measurements employ a good UV filter, there should be better consistency in color grading among grading labs and between colorimeter and human grading. This will eliminate the charge that blue fluorescing diamonds are being over-graded. If the "true color" is graded, a medium or strong blue fluorescing diamond of I color, for example, will have a perceived color in most viewing environments much whiter than a corresponding I color with no fluorescence. As long as there is no loss in transparency this should give fluorescent diamonds a real selling advantage, something they used to enjoy.
The second direction is to minimize the importance of "true body color" and embrace the fact that grading with a DiamondLite or other UV rich fluorescent light is yielding a color grade closer to the perceived color seen in the diamond in the environment it is most often viewed (natural daylight and office or home florescent lighting). Since everyone is currently using some form of fluorescent lighting as their color grading illumination why not stay with the status quo? Without consciously making any decision and by continuing to use unfiltered fluorescent light for grading, the trade has in effect already abandoned trying to measure the diamond’s elusive "true body color". Because of the inertia of human nature, this is the most likely path the trade may continue following by default. And of course this will continue to leave the labs open to the charge that blue fluorescing diamonds are being over-graded. On the other hand, anyone grading in natural daylight, such as that pouring thru the floor to ceiling windows of the pictured, Antwerp diamond bourse, is also open to the same criticism of over-grading blue fluorescent diamonds.
Epilogue
The September 1998 issue of "Jewelers’ Circular Keystone" has an article by Senior Editor Gary Roskin addressing "What GIA’s Fluorescence Study Ignored" wherein he states "To fully understand color grading, you need to appreciate the often overlooked matter of the light under which grading is done." He asks "Does strong blue fluorescence, whether perceived by a consumer or not, enhance the color grade of a diamond?" He then answers his own question in the affirmative saying that he has compared diamonds with strong and very strong blue fluorescence in UV free light compared to "normal", "traditional" light and "the difference can be quite dramatic, possibly by two or three color grades". As a gemologist with much trade experience he appears to be heading in the first direction acknowledging the difference between the GIA color grade using the unfiltered DiamondLite verses the traditional "true body color". However, he points out thru the words of John King, GIA Gem Trade Lab’s director of special projects, why GIA doesn’t use UV-free lights. King says "It’s not relevant because it doesn’t really exist anywhere". Roskin goes on to say "Remember, all diamonds from a century ago until now have been graded in light that has a small percentage of UV. Says James Shigley, GIA’s director of research, "We have this traditional way to look at diamonds, and that is the benchmark."" From Shigley’s and King’s remarks as well as those of Boyajian, it is clear that the GIA is headed in the second of the two directions.
FOOTNOTE SECTION
1. Vol. XXXIII, winter 1997
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2. "Diamonds", 1978, p.265
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3. Assignment # 35, p. 3
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4. Assignment # 35, p. 4
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5. Assignment. # 35, p. 6
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6. Assignment # 35, p. 6
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7. pp. 264-265
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another take - not all that accurate so I will not credit the source
About 20% of diamonds exhibit fluorescence. You have probably seen fluorescent minerals in natural history museums. Their fluorescence can be seen in darkened rooms with black lights. The effect is like a white shirt in a discotheque.
The most common fluorescent color is blue, and this can vary from weak or faint to very strong. Blue fluorescence can be an advantage, particularly in lower (below I) colored diamonds, because blue is the complimentary color to yellow. Adding blue compensates for yellow and makes the diamond appear whiter in any light that has an ultra violet component (e.g. daylight and halogen lighting).
What is Fluorescence?
Fluorescence is visible light emitted by electrons in a material that is being excited by electromagnetic energy (say a radiation like UV light or X-rays). As the electrons fall from a higher state of energy, to a lower state, they emit photons of light.
When the exciting energy source is removed (turned off), the fluorescence ceases instantly. If however, there is continued light emission (because the electrons gradually fall back to the lower energy state) after the source is removed, the phenomenon is called phosphorescence.
Is Blue Fluorescence Bad News? Not Necessarily,
Says GIA Study
Here are some extracts of the study “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds,” (1997) in the GIA journal that was reported in Rapaport Diamond Review in
For a number of years, the strength and color of fluorescence in a diamond have been singled out by many in the trade as an important characteristic of that diamond. Often the presence of moderate to strong blue fluorescence is applied across the board as a marker of lower offering prices, based on a belief that such fluorescence has an undesirable effect on the color appearance and transparency of a polished diamond.
At the same time, others in the trade have contended that overall appearance typically is not negatively affected by fluorescence. Before this study, however, there had not been any controlled investigation of this subject. To address this situation , GIA and GIA Gem Trade Laboratory researchers designed a visual experiment as a first step toward understanding how and what conditions fluorescence affects a diamond’s color appearance or transparency.
The purpose of this study was to explore the perceived influence of reported blue fluorescence in colorless to faint yellow diamonds when they were viewed in different positions and under different lighting conditions by observers from both within and outside the diamond industry.
Types of Diamonds Studied
Only about 35 percent of gem diamonds show any fluorescence, and of these, blue is by far the most common fluorescence color observed. A search the Gem Trade Laboraatory’s database from a recent time period showed that in 97 percent of those diamonds for which a fluorescence color was reported, that color was blue. Therefore, even though yellow fluorescence is also a concern in the industry, it is quite rare, so we decided to limit this study to blue fluorescence.
Four sets of six diamonds each were selected for the study. The six diamonds in each set had the same color grade, with the four color grades representing important commercial breakpoints: E, G, I, and K. All 24 diamonds were round brilliants, had good or better polish and symmetry, and were cut to similar proportions; most had clarities at or above the VS range. Since all these aspects of diamonds can cause differences in appearance, we tried to control them as completely as possible, leaving fluorescence as the one variable to be studied within each color set.
The diamonds in each set exhibited a range of fluorescence strengths that were typical of those most commonly encountered in the trade (see figure 1). Diamonds of extremely strong blue fluorescence, known as “overblues,” were not part of this study. Such diamonds have a noticeable oily or hazy appearance when excited by any of a number of light sources. Although diamonds described as very strong blue are routinely seen in the trade, a true “overblue” is rare.
Results of the Study
For the observers in this study, blue fluorescence had, at best, a subtle effect on color appearance and transparency. The non-trade observers made no consistent, meaningful distinctions of either color or transparency that related to fluorescence. Most of the experienced observers saw differences in color appearance, but less than half saw any differences in transparency.
Although we found some statistical correlation between color appearance and fluorescence, the responses varied from stone to stone, with some highly fluorescent diamonds in a color set singled out, while others of like strength in the same set were not. This inconsistency implies that other factors besides fluorescence affect color appearance for these different lighting and viewing conditions.
In the table-up position, diamonds described as strongly or very strongly fluorescent were, on average, reported to have a better color appearance than less fluorescent diamonds. There was a slight tendency for blue-fluorescent diamonds to appear less transparent table down in artificial light, but slightly more transparent when viewed table-up under sunlight.
There were also variations in perceived fluorescence effects for the different color sets. The effect on diamond color appearance was most noticeable in the lower colors (I and K), although in the marketplace the influence on price is greater in the higher colors (E and G). This study challenges the industry notion that fluorescence usually has a negative effect on better-color diamonds. GIA’s results show that the industry would be better served by considering each individual diamond on its own visual merits.
Blue White: a Brief History of Fluorescence
Posted: 4/9/1998
Extracts of an article by Martin Rapaport in the Rapaport Diamond Report April 1998
Once upon a time before the diamond industry standardized to GIA colour grading terminology the term Blue White (Blauweiss) was used to describe the finest colour white diamonds. The original Blue White diamonds came from South Africa's Jagersfontein mine. The best Jager stones were highly transparent (clear and colorless) with a bluish tint due to fluorescence. Ironically, during the early part of the 20th century fluorescence was seen as something that had a very positive impact on top colors. The extra sparkle fluorescence provided when the diamond was seen face up in sunlight was accepted as verification of the diamonds high color. Blue White diamonds were avidly sought out by the trade and consumers who paid higher prices for diamonds with fluorescence. Contrary to current market conditions, fluorescence added value to high color diamonds.
Now the history of what happened to fluorescence is very interesting and informative. The trade had something very good going with fluorescent Blue White diamonds, but they blew it. Instead of maintaining consumer confidence in Blue White the trade began selling all types of lower color diamonds as Blue White. The term Blue White and the underlying concept that blue (i.e. fluorescence) added value to white (colorless) diamonds was so abused by the trade that in 1938 the U.S. Federal Trade Commission outlawed the use of the term Blue White for anything but blue diamonds.
Abuse of the term Blue White and the subsequent FTC restrictions undoubtedly encouraged the establishment of GIA color grading system. Color grading systems try their best to differentiate between the amount of color or tint in a diamond (i.e. the degree of its transparency or lack of any color) and the sparkle effect provided by fluorescence (fluor) in various lighting environments. In fact, one primary reason the GIA developed standardized color grading using a Diamondlite box with a controlled light source was to be able to color grade diamonds while minimizing the
influence of fluor.
The bottom line is that blue fluor enhances the color of diamonds in almost all lighting conditions. Is this bad? If not, why does the trade pay lower prices for fluor diamonds?
In some instances the trade does pay more for fluor. Typically J color and lower fluor stones bring a better price. This is because they look whiter to the trade. However, when it comes to higher D-F colors in VS and better clarity grades fluor is discounted. In general the more expensive the diamond the greater discount.
Some people believe that the trade is making a mistake and fluor diamonds are wrongly discounted due to misinformation and a misguided herd instinct. The theory is that the trade misunderstands the impact of fluor on higher color stones which is minimal because there is very little yellow color in the stone to improve upon. Suppliers believe that if they could convince buyers not to discount fluor they would make more money and improve liquidity.
The GIA has just published a research report on the effect of blue fluor on the appearance of diamonds. Interestingly the GIA concludes, "This study challenges the industry notion that fluor usually has a negative effect on better color diamonds."
The GIA is saying that lower prices for high color fluor stones do not make sense. So why does the trade discount higher color fluor diamonds? Are the diamond markets irrational?
This writer tends to believe in the rational market theory. In other words, over the medium and long term markets are never wrong because prices reflect the combined wisdom of everyone everywhere. The old market rule, "You can fool some of the people some of the time and the rest of the people the rest of the time, but you can't fool all the people all the time," makes perfect sense. It is especially true when people are voting with their money. While education and information certainly shape demand, add value and influence market forces that set prices, over the long term, by definition, markets do not make mistakes, they value things correctly.
So why does the trade discount fluor? Let's view the market from the perspective of a diamond trader and consider some recent diamond history.
As the investment diamond boom developed in the mid 70's and prices for D-IF's skyrocketed, very strong blue over-white or over-blue hazy diamonds needed to be weeded out of distribution. Since traders were flipping certs over telex machines the easiest way to do this was by avoiding strong blues (SB). Sure some SB's were fine but you had to look at them and convince your customer they were ok. In some instances fine jewelers resisting mixing fluor goods with non-fluor goods because the stones face up differently. Also, the French who were important buyers at the time hated fluor. This may be because fluor means 'false color' in French.
Perhaps if certs didn't mention fluor no one would have cared about it. However, since it was there on the paper dealers figured they could use it to haggle and do some price differentiation. In soft markets dealers could discount fluor stones without disturbing the market value of inventory too much.
Traders were and still are disturbed by the correlation between over-graded colors and fluor. Nothing upsets a trader more than buying a G and finding out the stone is really an H because some lab made a mistake. Unfortunately, the probability of a lab over-grading a fluor stone is much greater than a non-fluor stone and a large percentage of high color mistakes turn out to be fluor. Over time mistakes pile up in the market since no one wants to buy them. This reinforces the notion that over graded stones have fluor. Perhaps if the labs graded fluor more conservatively dealers wouldn't be so afraid of them.
Korea’s scandal also had a great impact on world prices for fluor goods. See our June 1993 article "The Korean Blues" for full details. In short, the Korean labs over-graded the color of fluor stones which encouraged huge imports of fluor stones. In the early 90’s Koreans were the worlds largest buyers of fluor stones and as much as 50 percent of the stones sold in Korea were fluor. The bubble burst in 1993 when an investigative TV special informed Korean consumers that their fluor stones were over-graded. Korean consumers found out their G's were really H's and no one in Korea ever trusted a fluor stone again. Not only did the Korean buyers stop buying fluor stones they became net sellers as consumers insisted sellers replace the fluor stones.
As the market struggled to deal with the Korean problem along came the Russians dumping diamonds. Guess what? A huge percentage of Russia's diamonds were fluor. Now it is very nice for the cutters and the GIA to explain to everyone that fluor stones are OK (assuming they are not over-graded). But let's consider supply and demand from the dealers perspective.
I'm a dealer looking for D-F, IF-VVS goods. Expensive stones. 70 percent of the stones offered to me are fluor 30 percent are not. If prices are the same or near same, which stones do you think I am going to buy? Frankly, I don’t care what anyone says about fluor or even what the stones look like. I trade scarcity. I trade liquidity.
One primary reason dealers discounted fluor stones was to protect the market from the great inflow of Russian goods. The overriding factor justifying the market discount for fluor was scarcity. If D’s were expensive because they were rare it was reasonable to expect that scarcer D’s (i.e. D’s without fluor.) would be even more expensive. The trade did not and does not necessarily price diamonds based only on appearance. Scarcity also has a great influence on price.
Obviously from the market perspective there appears to be a reasonable basis for price discrimination against fluor. While this article supports the rational markets theory it is important that we pay careful attention to what the GIA is saying. It may very well be that the trade is over-discounting fluor. If fluor diamonds are graded accurately under ideal laboratory lighting conditions blue fluor. stones have an advantage in that their color improves in normal daylight.
While education can play an important role changing buyers perception about the negative impact fluor has on higher color diamonds it will have to backed up by solid results. In other words the labs are going to have to be very serious about not over-grading the color of fluor stones even though these stones tend to appear whiter than they are. Furthermore the labs must clearly indicate on their grading reports instances where milky fluor detracts from the quality of the diamond. Only then will the trade and consumers have the confidence to pay better prices for fluor stones.
Regarding relative scarcity, based on the GIA research fluor stones are scarcer than non-fluor stones. The reason the availability of fluor stones is greater in the market is because they are more difficult to sell. Over the long term if the trade changes its perception about fluor goods and they sell through on a more liquid basis market availability may decline so that there is no longer an oversupply of fluor stones in the market.
From an economic perspective, there appears to be little benefit to the trade by increasing prices for fluor stones. It is likely that any price benefit will be absorbed by higher CSO prices for rough. Furthermore, the availability of fluor stones helps the market adjust to varying degrees of availability. When the availability of higher colors are tight, the discount for fluor drops as buyers more readily accept fluor because there are fewer alternatives available. On the other hand when goods are plentiful the fluor discount grows protecting prices for non-fluor goods. This assures less price volatility for higher colors.
In conclusion, the GIA report is interesting and important. To some degree the GIA can influence market behavior, encourage greater acceptance of high color fluor stones and ultimately shift the demand curve for fluor diamonds. However, it is important for us to recognize the sophisticated nature of price making forces in the free market and the role of the market in deciding what is and is not a better diamond through pricing. The beauty of the free market is that it is a real changing live world, open to all information, influences and opinions. Yet at the same time markets provide real numbers that reflect the consensus of all participants as to the real value of diamonds.
By Michael Cowing, MS, FGA, NJA © Copyright 1998 All rights reserved.
Gemological Institute of America, (GIA), recently published in their quarterly journal, "Gems & Gemology", 1 the results of a human experiment in the observation of diamonds with various amounts of blue fluorescence. The article was entitled "A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds". An introductory editorial by GIA’s president William Boyajian indicates that the study "challenges the perception held by many in the trade that UV fluorescence generally has a negative effect on the overall appearance of a diamond". He makes it clear that this is a false perception, which the GIA hopes this study will help to dispel. He says this study "should bring into question the trade’s lower "bid" prices for moderate to highly fluorescent diamonds in the better colors".
Historically, the GIA has been the principal source of information in the area of diamond color grading for gemologists, appraisers and the diamond trade, so this article will generate much discussion. Because of the GIA's stature and credibility with the trade and the buying public, this article will be quoted by many to improve the relative salability of diamonds with the property of medium or strong blue fluorescence indicated on their grading report.
To help disseminate the message of this study to the trade, an abbreviated version of this article was published in the April 1998 issue of the "Rapaport Diamond Report". In the same issue Martin Rapaport responded with a thoughtful article, entitled "Blue White" in response to the GIA study’s conclusions. In it he explained the trades historical handling of blue fluorescence in diamonds from a pricing and marketing perspective. He points out why the trade discounts fluorescence in the higher gem quality diamonds, and how it came about that fluorescence comments, indicated on a diamond grading report, became undesirable. He concludes: "Obviously from the market perspective there appears to be a reasonable basis for price discrimination against fluorescence". He acknowledges "If fluorescent diamonds are graded accurately under ideal laboratory lighting conditions blue fluorescent stones have an advantage in that their color improves in normal daylight". Finally, he admonishes that "changing buyers perception about the negative impact fluorescence has on higher color diamonds … will have to backed up by solid results. In other words the labs are going to have to be very serious about not over-grading the color of fluorescent stones even though these stones tend to appear whiter than they are".
As a gemologist and member of the diamond trade, the author has been involved with this issue since the early 80’s and would like to make a contribution by addressing the following questions, which both articles should raise in the minds of their readers:
Are the labs over-grading blue fluorescent diamonds? If so, why? How can the labs insure they are not over-grading blue fluorescent diamonds and convince the trade of this? What can be learned from this new study beyond Boyajian’s and Rapaport’s conclusions? These questions are examined in the historical context of what gemologists have learned and taught the diamond trade regarding fluorescence and diamond color grading over the last 30 or so years.
The majority of natural gem quality diamonds contain nitrogen as an impurity. Depending upon the amount of nitrogen and how it is distributed throughout the diamond, this impurity causes the slight tints of yellow to which the GIA assigns the letter color grades from D to Z. This type of diamond is categorized as Type Ia. For simplicity and because it covers most of the gem color white diamonds, the GIA and this discussion address mainly this Ia diamond type. However the principles discussed are extensible to the other categories. This same nitrogen impurity in the type Ia diamond, depending upon the percentage and distribution of nitrogen, may cause fluorescence of varying intensities of blue or bluish-white.
Fluorescence is the emission of visible light from a substance being stimulated by invisible, ultra violet, (UV), energy such as that contained in sunlight and indirect sunlight. Gemologists look for this property of fluorescence in diamonds and other gems by employing ultra violet lamps. These UV sources use either a high or low-pressure mercury vapor tube with a filter that removes visible light emitted by the tube. This leaves energy or radiation in the short and long wave UV wavelength range of 200 nm to 400 nm. The two highest energy wavelengths put out by these tubes are 366 nm, which is in the long wave UV range, and 254 nm, which is in the short wave UV range. These wavelengths are selectively filtered to produce long and short wave UV energy for testing fluorescence. Another popularly used source of long wave UV is a low-pressure mercury vapor tube that excites a special coating which then emits long wave UV. When a diamond with blue fluorescence is illuminated with invisible long wave UV energy from one of these lamps in an otherwise dark environment the diamond glows blue. Short wave UV energy also stimulates blue fluorescence, but to a much lesser extent, leaving long wave UV the dominant source that produces this effect.
The GIA Article makes the point that a group of two nitrogen atoms, the A aggregate, tends to quench fluorescence while a group of three nitrogen atoms, called the N3 center, produces blue fluorescence. Since a single diamond may contain varying amounts of these nitrogen defects, the result may be anything from no fluorescence to extremely strong blue fluorescence. The GIA says this confounds "the trade notion that nonfluorescent diamonds are more "pure" than those that fluoresce, since there are nitrogen- related centers that extinguish fluorescence as well as those that cause blue fluorescence." They are making the important point that blue fluorescence or lack thereof is a property of diamond, not an indicator of "purity", since a nonfluorescent diamond may often have a greater percentage of nitrogen impurity than one that is blue fluorescent.
The light yellow tints in a Type Ia diamond combine with the various amounts of blue fluorescence to give the diamond its perceived color. Gemologists and the trade define and refer to the diamond’s "true color" as that color that a diamond exhibits when viewed under illumination devoid of any UV energy that would excite fluorescence. Because all the light sources regularly used to view and grade diamonds contain some amount of long wave UV energy the "true color" of a strongly blue fluorescent diamond is never seen. What is seen is the perceived net color. This net color includes whatever amount of blue fluorescence is stimulated by the light source’s UV energy. To explore the perplexity of perceived color verses "true color", we need to discuss in detail how gemologists have historically measured and graded color in a diamond.
Of primary importance in diamond color grading is the illumination used to view the diamond during grading. Under what illumination should the diamond be viewed in order to properly grade diamond color?
There are three general types of illumination, which have been used in diamond color grading. The first is the various forms of natural daylight. The second is fluorescent lighting, and the third is the various incandescent, filament type, light bulbs from high intensity tungsten to quartz halogen. Each of these forms of illumination has their advantages and disadvantages for use in color grading. Historically, the best form of natural daylight for color grading was found to be northern daylight. Eric Bruton’s classic book from the 70’s, 2 defines northern daylight to be "daylight from a North-facing window in the Northern Hemisphere and from a South facing one in the Southern". Grading was typically done during the daylight hours when the sun was high enough in the sky to avoid the reddish tint in early morning and late afternoon light. The very slightly bluish-white northern daylight made an ideal illuminant to detect the slight tints of yellow typical in gem quality diamonds.
To further the understanding of the properties of this light, which made it desirable for color grading diamonds, it is useful to introduce the unifying concept of color temperature. The measure of temperature described here is degrees Kelvin (K). Degrees Kelvin is just degrees centigrade (C) plus 273, because absolute zero, to which Kelvin temperature is referenced, is -273C.
When a substance such as the tungsten filament in an incandescent light bulb is heated to sufficiently high temperatures it radiates energy over a whole spectrum of different wavelengths. The spectrum extends from the very long infra red waves, which produce the sensation of heat, thru the 750 nm to 400 nm waves which produce the sensation of color from red to orange, yellow, green, cyan, blue, violet and then on into the invisible ultra violet short wavelengths between 400 nm and 200 nm. The perceived color of this spectrum is a function of the balance or distribution of energy over the visible wavelengths. When the filament temperature reaches 1500K to 2500K the visible wavelengths combine to give a reddish tint to the illumination. As the filament is heated to 2800K to 3200K the yellowish- white light of incandescent bulbs is produced. The higher the temperature is raised as in quartz halogen bulbs, the less yellow and more neutral-white the emitted light becomes. Incandescent lights reach a practical temperature limit at about 3400K, but at a color temperature of 5500K to 6500K the balance of energy in the visible wavelengths tilts to the very slightly bluish-white of northern daylight.
Compare color grading under a yellowish-white, incandescent illumination of 3200K to grading under the 6500K, bluish-white, northern daylight. You will find, as did the early color graders, that slight tints of yellow are more easily observed in the complimentary very slightly bluish-white northern daylight than in the yellowish-white light of incandescent sources. Thus, the color temperature close to northern daylight of 5000K to 6500K became the standard for color grading diamonds.
However, natural, northern daylight has another property that complicates the diamond color-grading picture. It is rich in both long and short wave UV energy. This invisible UV part of the spectrum of daylight excites the blue fluorescence in diamonds having this property. Early on, it was recognized that the perceived color grade of typical gem quality diamonds was a combination of the faint yellowish tint in the diamond and any blue fluorescence caused by UV from the illuminating source. Since blue and yellow light are complimentary, they tend to cancel. A highly blue fluorescing, yellowish diamond will show its yellowish nature when viewed under illumination with a minimum of UV such as incandescent light, but will appear increasingly colorless in lighting with increasing amounts of long wave UV. Finally, in the UV rich illumination of daylight it may appear colorless or even slightly bluish-white. The plate glass windows, thru which the northern daylight enters, such as the floor to ceiling windows of the pictured, Antwerp diamond bourse, filter out most of the short wave UV energy. However, most all the long wave UV that is the main cause of fluorescence remains present.
This presented a real dilemma to early diamond graders including Shipley, the GIA’s founder. On the one hand the color temperature of northern daylight was ideal for color grading diamonds with slight tints of yellow, but at the same time daylight’s long wave UV energy was causing blue fluorescent diamonds to look whiter than they did when compared under incandescent illumination having a minimum of UV energy. Since the color of a fluorescent diamond changes as a function of the illumination under which it is observed, what should be the standard illumination to grade this color? Early on the GIA and others decided to separate the whitening effect of blue fluorescing diamonds from the basic yellowish tint by designing a standard light source with a close to northern daylight color balance of 5000K to 6500K, but unlike northern daylight having a minimum of UV.
The GIA Diamond Course from 1969, 3 stated "A large percentage of diamonds fluoresce, usually blue; and the fluorescence, if sufficiently intense will alter the color of such a stone when observed under a light source emitting ultraviolet rays. Since this occurs under daylight examination the most desirable conditions are to be encountered under a balanced artificial light with a minimum of ultra violet content." This is perhaps the most logical approach to the dilemma presented by fluorescence. By changing the standard illumination for color grading from northern daylight with a lot of UV to incandescent illumination with a minimum of UV, the color advantage that blue fluorescing diamonds possessed in daylight was minimized in the grading.
The GIA produced their first diamond color grading instrument, called the DiamondLite, using an incandescent filament type of light source and a "daylight filter" which produced "the equivalent of north light without the UV radiation." 4 At the same time the GIA Diamond Course stated that "a reasonably good substitute for the DiamondLite can be made by adapting a simple desk lamp fixture containing cool white fluorescent tubes." 5 However, they caution "the disadvantage of this kind of illumination is that fluorescent tubes emit a significant percentage of ultra violet radiation. Although this does not affect the grading of nonfluorescent stones, it causes fluorescent diamonds to be graded higher then is actually warranted due to the neutralizing, or masking, effect of the fluorescent color on the true body color." 6 Gemologists graduating from the GIA in the 1969 time frame came away with the principle that diamonds should be graded for color under a daylight balanced artificial illumination absent the UV radiation energy contained in natural northern daylight and also contained in fluorescent lighting. They learned that grading in daylight or fluorescent light with the attendant UV radiation will result in over grading a blue fluorescing diamond. This has become the conventional wisdom among gemologists since that time. Eric Bruton’s book, "Diamonds", published in the 70’s, indicated that gemologists worldwide shared these views on illumination for diamond color grading. In a section of his book under conditions for color grading, 7 he said a "very important consideration is that any fluorescence in the stone must be suppressed"…."It is therefore important to grade stones in white light that is relatively free of ultra-violet".
What has happened since that time? By the 70’s we find gemologists and the diamond trade worldwide are universally using some form of fluorescent light to grade color in diamonds. The later versions of the GIA DiamondLite have substituted Verilux brand, fluorescent tubes for the daylight corrected incandescent light source in the early model. This is the very same source of grading illumination that was said to result in the over grading of fluorescent diamonds. Does that mean that by their original color grading standards, gemologists are over grading blue fluorescent diamonds? If so, would that not make a good additional argument for discounting the "bid" price of blue fluorescent diamonds?
First of all there is indeed evidence to suggest that going by the original, UV free, diamond grading standards, the trade and anyone grading with fluorescent lighting is over grading diamonds with strong or very strong blue fluorescence and possibly even medium blue. This varies little, except in degree, from the over grading that many felt was occurring when natural northern daylight was being used for color grading. By using fluorescent lighting as the standard illumination for diamond color grading, gemologists have in effect redefined the standard amount of UV to be that contained in fluorescent lighting. Perhaps this is an acceptable alternative to grading in the absence of UV, but it presents its own set of problems. Most importantly, fluorescent illumination containing significant UV energy certainly does not reveal the "true color" as defined by the early gemologists and as understood by the trade. In addition, the amount of UV exciting the fluorescence in the diamond being graded varies with the tube’s manufacturer, with the tube’s age and with the distance the diamond is held from the tube during grading.
The new GIA article indicates that a digital radiometer was used to measure the UV content of each of the light sources that were used in the study. They found no appreciable differences in long wave UV content from one source of fluorescent lighting to the next including the Verilux tubes used in their standard DiamondLite. They also found "indirect daylight through our windows has about as much UV radiation as the fluorescent light sources". If fluorescent lighting and daylight have a similar amount of UV radiation as the GIA measured, it would be expected that blue fluorescing diamonds would be perceived to be relatively whiter in daylight and under the DiamondLite than they would be if no UV radiation were present.
The four, color sets of diamonds used in the GIA observation studies were carefully chosen from more than 1000 diamonds, so they would be similar to one another in all respects except their fluorescence. Of course, their colors were graded in the Verilux illumination of the DiamondLite, illumination that is the standard for grading diamond color at the GIA Gem Trade Labs. Excellent quality, color photos were published with the article of each of the four, six stone sets whose colors were E, G, I and K. These photos appear to provide an indication that at least some of these diamonds have been graded higher than they would have been under the old color corrected incandescent illumination of the first DiamondLites. Because the photos were taken in incandescent illumination, relatively free of UV energy, the blue fluorescing diamonds should loose most of their color advantage. Under incandescent illumination, comparing within a set of identical color grade should reveal the approximate, relative "true color" of these diamonds. For example, the I color set’s diamonds have measured fluorescence, from left to right, of: 1. Medium, 2. Very Strong, 3. Faint, 4.Strong, 5. None, and 6. Strong. If you study carefully those six stones in the face up photo, stones 2, 4 and 6 appear to have more color than the other three in spite of having been graded identically as I colors under the Verilux tube of the DiamondLite. It is more than a coincidence that these are the three with the strongest blue fluorescence, indicating that they have been overgraded relative to what they would have been had the illumination used for grading been the low UV, incandescent illumination used in the photo. The other sets are less consistent in showing this effect, but the highest fluorescing member of each of the E, G, and K color sets appears to be the most tinted of its respective color set. It is important to note that these differences in color appearance are not apparent in photos taken of the table-down view of these same diamonds, the view under which they were graded. If these same photographs were retaken using natural daylight with more UV than the Verilux tubes have, what would be the expected outcome? Using daylight film to take the photographs, you would find that the most yellow tinted diamonds, which were the most fluorescent members in each set, would now be the least tinted and might even appear bluish-white.
All this brings up another interesting problem for gemologists and anyone who uses colorimeters or spectrophotometers to assist them in diamond color grading. The GIA and many other organizations and manufacturers sell these instruments to assist the human eye in color grading diamonds. Colorimeters use incandescent light sources to make their measurements of color. Because of the differing UV content in incandescent vs. fluorescent lighting the colorimeter’s measurement of color in blue fluorescing diamonds will differ from the measurements the human eye makes under fluorescent lighting. This is a further dilemma for gemologists to ponder.
So we have come full circle. Thirty or more years later, we are again facing the question of whether the illumination under which diamonds are graded should contain long wave UV, and if so how much? We can stand pat with the GIA’s and the trade’s use of fluorescent light sources with their attendant somewhat variable amounts of UV as the de facto standard, and live with the fact that a blue fluorescent diamond will grade whiter due to the UV energy contained in this illumination. After all a blue fluorescent diamond does appear a whiter color in all but perhaps incandescent lighting. The result will likely be a continuation of the distrust of color grading done on blue fluorescent diamonds as discussed in Rapaport’s article.
There is an alternative course of action that is being taken recently by a number of gemologists and gem labs. They are adhering to the early gemologists’ teaching that the body color of the diamond should be graded in an illumination that is absent UV energy. They have found a simple, inexpensive method to filter out the UV energy from all light sources be they natural, fluorescent or incandescent. GE manufactures a window glass substitute called Lexan, which is a plastic that filters out virtually all long and short wave UV. By filtering the light thru a sheet of Lexan or other UV filter, all the three types of light sources used for color grading would be put on the same footing, namely no UV. This eliminates the possibility of the so-called over-grading of blue fluorescing diamonds due to UV. Of course it is even stricter a standard than the original DiamondLite since the tungsten filament light source it used still contained the minor amount of UV present in all incandescent lights. This solution to the problem should go a long way toward correcting the trade perception that labs are over-grading blue fluorescent diamonds. There would be much better correlation, when it comes to blue fluorescing diamonds, between colorimeter and spectrophotometer grading and human graders using fluorescent lights and natural lighting environments.
Whichever choice a gemologist or a member of the diamond trade makes, whether to continue using unfiltered fluorescent lighting or eliminate the UV energy by filtering, he should be aware of the impact of his decision on the color grading of blue fluorescent diamonds. Keep in mind that there are differing views about the degree to which the UV content in standard fluorescent lighting is affecting the grading of blue fluorescent diamonds compared to their nonfluorescent counterparts. While the GIA’s study concluded that "in general the results revealed that strongly blue fluorescent diamonds were perceived to have better color appearance when viewed table up" they found "no discernable trend table-down". Since this is the position used for color grading, perhaps, except for strong blue fluorescence, the grading is close to the "true color." A large number of gemologists and the trade appear to believe differently, and perhaps by filtering out the UV, these concerns can be allayed.
A final issue that both articles address is the perception held by most that blue fluorescence is sometimes associated with an attendant milky or hazy appearance. Rapaport admonishes "the labs must clearly indicate on their grading reports instances where milky fluorescence detracts from the quality of the diamond". At what point along the scale of fluorescent strength from faint to very strong blue can this milky appearance be noticed? Here again there is a difference in opinions. However, everyone acknowledges that this effect, which is a loss in transparency, has a significant negative impact on value and salability when it is present. This was a quality factor that the GIA study asked its participants to evaluate in order to make a contribution to answering this question. They did not include in the study "diamonds with extremely strong blue fluorescence and a distinctive oily or hazy appearance". In the range of fluorescent strengths, including very strong, the study found that "most observers did not detect any differences in transparency among diamonds in a given color set. Of those who did see a difference under fluorescent lighting, it was only apparent in the table-down position. These results challenge the notion that strongly fluorescent diamonds typically have a hazy appearance". The GIA believes that the study shows, up to and including strong blue fluorescent diamonds, there is no noticeable decrease in transparency in the normal face up viewing position. The study’s findings indicate that this may be one negative perception of blue fluorescent diamonds, harbored by the trade that may not be warranted except in the case of extremely strong blue fluorescence.
Concluding Remarks
The author encourages you to read or reread the GIA’s article and Rapaport’s response in the light of this discussion. Two possible simplified conclusions may be reached as to the correct direction the gemological community and the trade should take. They both have merit.
The first direction is to pursue measuring the "true body color" and minimize the fact that most diamond viewing environments enhance the whiteness of blue fluorescing diamonds because they contain significant amounts of UV energy. The grading labs and the trade could implement, using Lexan or other UV filters, a color grading environment absent UV in order to grade the "true body color" as taught by the early GIA Diamond Course. If all color-grading measurements employ a good UV filter, there should be better consistency in color grading among grading labs and between colorimeter and human grading. This will eliminate the charge that blue fluorescing diamonds are being over-graded. If the "true color" is graded, a medium or strong blue fluorescing diamond of I color, for example, will have a perceived color in most viewing environments much whiter than a corresponding I color with no fluorescence. As long as there is no loss in transparency this should give fluorescent diamonds a real selling advantage, something they used to enjoy.
The second direction is to minimize the importance of "true body color" and embrace the fact that grading with a DiamondLite or other UV rich fluorescent light is yielding a color grade closer to the perceived color seen in the diamond in the environment it is most often viewed (natural daylight and office or home florescent lighting). Since everyone is currently using some form of fluorescent lighting as their color grading illumination why not stay with the status quo? Without consciously making any decision and by continuing to use unfiltered fluorescent light for grading, the trade has in effect already abandoned trying to measure the diamond’s elusive "true body color". Because of the inertia of human nature, this is the most likely path the trade may continue following by default. And of course this will continue to leave the labs open to the charge that blue fluorescing diamonds are being over-graded. On the other hand, anyone grading in natural daylight, such as that pouring thru the floor to ceiling windows of the pictured, Antwerp diamond bourse, is also open to the same criticism of over-grading blue fluorescent diamonds.
Epilogue
The September 1998 issue of "Jewelers’ Circular Keystone" has an article by Senior Editor Gary Roskin addressing "What GIA’s Fluorescence Study Ignored" wherein he states "To fully understand color grading, you need to appreciate the often overlooked matter of the light under which grading is done." He asks "Does strong blue fluorescence, whether perceived by a consumer or not, enhance the color grade of a diamond?" He then answers his own question in the affirmative saying that he has compared diamonds with strong and very strong blue fluorescence in UV free light compared to "normal", "traditional" light and "the difference can be quite dramatic, possibly by two or three color grades". As a gemologist with much trade experience he appears to be heading in the first direction acknowledging the difference between the GIA color grade using the unfiltered DiamondLite verses the traditional "true body color". However, he points out thru the words of John King, GIA Gem Trade Lab’s director of special projects, why GIA doesn’t use UV-free lights. King says "It’s not relevant because it doesn’t really exist anywhere". Roskin goes on to say "Remember, all diamonds from a century ago until now have been graded in light that has a small percentage of UV. Says James Shigley, GIA’s director of research, "We have this traditional way to look at diamonds, and that is the benchmark."" From Shigley’s and King’s remarks as well as those of Boyajian, it is clear that the GIA is headed in the second of the two directions.
FOOTNOTE SECTION
1. Vol. XXXIII, winter 1997
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2. "Diamonds", 1978, p.265
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3. Assignment # 35, p. 3
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4. Assignment # 35, p. 4
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5. Assignment. # 35, p. 6
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6. Assignment # 35, p. 6
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7. pp. 264-265
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another take - not all that accurate so I will not credit the source
About 20% of diamonds exhibit fluorescence. You have probably seen fluorescent minerals in natural history museums. Their fluorescence can be seen in darkened rooms with black lights. The effect is like a white shirt in a discotheque.
The most common fluorescent color is blue, and this can vary from weak or faint to very strong. Blue fluorescence can be an advantage, particularly in lower (below I) colored diamonds, because blue is the complimentary color to yellow. Adding blue compensates for yellow and makes the diamond appear whiter in any light that has an ultra violet component (e.g. daylight and halogen lighting).
What is Fluorescence?
Fluorescence is visible light emitted by electrons in a material that is being excited by electromagnetic energy (say a radiation like UV light or X-rays). As the electrons fall from a higher state of energy, to a lower state, they emit photons of light.
When the exciting energy source is removed (turned off), the fluorescence ceases instantly. If however, there is continued light emission (because the electrons gradually fall back to the lower energy state) after the source is removed, the phenomenon is called phosphorescence.
Jennifer5973
Ideal_Rock
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Not very scientific but the diamonds I get the most compliments on have at least a moderate amount of flourescence...ad these are F to H colored stones... I don't know why, but my friends/colleagues/family always seem to grvaitate toward the stones in things I know have flourescence.
My understanding is that in a minority of circumstances, flourescence can cause a milkiness in the stone in strong sunlight but I have never seen this in person.
Hmmm
My understanding is that in a minority of circumstances, flourescence can cause a milkiness in the stone in strong sunlight but I have never seen this in person.
Hmmm
Crimson - My earrings have flour. One stone is faint and one stone is medium. I'd love to see what strong flour. would look like. I get more compliments on my earrings, in fact most times I catch people starring at them when they're talking with me and they always comment. I love them in any light but they're EXCEPTIONAL in the evening. I plan on seeking out a stone for my ering with flour.
I wouldn't by any means rule out the G with the flour. Good luck whatever you decide.
I wouldn't by any means rule out the G with the flour. Good luck whatever you decide.
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highendgems
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i would say a well cut diamond with properly graded H color or above should have an absense of fluoresence. this is proven as you will almost never see top of the line, well cut diamonds of a good make with fluor. what SLIGHT OR MODERATE fluor. can do is take an I or below colored stone look a bit whiter. if the stone does not have inclusions visible to the eye, and has good color, fluor. will make the stone look oily and dark (more blue than white flashes). it seems alot of people say fluor. is not that bad--i just do not agree. whatever you do, stay away from yellow fluor.
pricescope
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aljdewey
Ideal_Rock
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I wholeheartedly disagree with this. Several of the experts have noted that stones with medium or faint fluorescence are completely no problem. Further, they've all noted that an overwhelming majority of stones with strong blue fluorescent aren't a problem either.....it's just important to be mindful when considering a strong blue fluor stone to check for milky/oily.
Outside of that, blue fluor doesn't detract AT ALL from diamonds----whether they are I, H, G, or even D color. Yes, high-color stones with fluorescence are usually discounted a bit----not because they are less desirable looking, but simply because they do have fluor.
aljdewey
Ideal_Rock
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Simply not true. How many diamonds have you bought? And of said diamonds, how many exhibit bl. fluor? For that matter, how many diamonds have you *seen* with blue fluor. to base what *you* deem as credible information?
Did you read the articles above? *Those* are written by people who actually *look* at diamonds everyday. The GIA is not a slanted organization out to prove something about blue fluor.
Can you please explain your creditials to make an opinion such as yours? I'm sure you will not as you don't have any.
highendgems
Rough_Rock
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Oh really, is that why you had to go to several jewelers to verify your diamond specs? Is that why you thought "ball of fire" was an accurate GIA cert term? Is that where you learned your plethera of misinformation?
So, as a GIA Gemologist *why* exactly do you not support the GIA study on Bl. Fluor?
BTW, I'm not satifying my beliefs. I am buying by my beliefs. Not accidently BTW.
strmrdr
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mike04456
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This is a rather theoretical Q, I know, but if you find one min....
There is something I do not understand: usually any differentiating characteristic that does not blatantly detract from a diamond's apperarence produces a price increase, not a discount for those stones. Why are fluorescent diamonds on average cheaper? I understand why strong or stronger flourescence produces a discount, but why is this nasty gossip about oily diamonds useful to anyone? After all, given that 1/3 of diamonds sold show some fluo, it does no stryke me as a practical thing to drive customers away from them. Well, I could be wrong. Ideas?
mike04456
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Any economist will tell you that markets are not always rational. Myths and superstitions can affect demand and prices even when they have been repeatedly debunked. The diamond business has a tremendous amount of tradition and inertia--people doing things simply because they've always done them that way--so it's not surprising that this price structure persists despite a lack of evidence to support it.
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Thanks! At least I have some clue now...
True, rational evidence is not always fast to win terrain, but interest is. If this is an old myth not a new fad, I guess that whatever commercial interest started it (it could not really that ancient, since the whole notion of fluorescence is not as old as wizardry) is old enough and deeply buried. I would imagine that in some forgotten day fluorescent diamonds might have gotten the same hype built around as the "warped" diamonds in today's Fredisms. Oh well.
diamondsR4ever
Rough_Rock
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I would agree that anything above faint flr. is not as desirable on higher-end ideal cut stones (colored H, VS clarity and above). You should look at the stone yourself to check for hazy or oily spots (especially in sunlight) and if you like it, then that is all that matters. Just know that on paper, it is worth less--probably around 5% less if listed as medium flr. and as much as 8% less if strong flr. As you go down in diamond color grades below J color, a bit of blue flr. (as much as medium) may bump up the price value by as much as 3-5%. You can check flr. with a blacklight in a dark room...wooh, disco time.
Oh, and to get to your specific point about G color: If stone is really well cut and you are spending a bunch of cash--you should try to aim for no flr.
Oh, and to get to your specific point about G color: If stone is really well cut and you are spending a bunch of cash--you should try to aim for no flr.
Mara
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diamondsR4ever
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aljdewey
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I'm sorry......I don't believe this AT ALL. I'm a regular consumer, and I've found most of the information you've provided to be riddled with error and factually incorrect inforamtion.
I'd more readily believe you were the Prince of England before I'd seriously think you were ANY kind of accredited gemologist. It's just not so, and you're not fooling anyone.
aljdewey
Ideal_Rock
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REALLY? So let me see if I understand this correctly? You're saying that we should believe that there are TWO wingnuts that both work at the same company and BOTH argue against fluorescence?
HEG, I'm sure you do have accreditation.......as a full-time liar.
There is NO record of any S.R.I. USA in the country. If it had 150 people, there would be a record of it SOMEWHERE.
This is really pathetic.
mike04456
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Well, there is an SRI, but it's a Silicon Valley R&D outfit. They certainly don't sell gems... or humidors.
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