Extinction

[Michael_E]

Absolutely 100% correct and this is why this thread is so confusing. The terminology is used differently in diamond world and coloured gemstone world!

Extinction = a gem cut with areas that do not return light - no matter what you do or how you look at it or where the light is/isn't.

This last sentence is THE reason for confusion. WHERE the light is or isn't, IS everything with any gem. Unless a gem has inclusions which distribute light evenly through the stone, or is fluorescent in which case light is produced evenly through the stone, any gem will show evidence of what people here call, "extinction", or dark areas in a gem. In many cases the dark areas being seen are due to poor lighting and are not a function of the cut of the stone or it's material properties. This is definitely a function of where the light is coming from and has nothing to do with the quality of cutting and little to do with the darkness of the material being used. I swear, one of these days I'm going to be reading that someone is not happy with the stone they've just bought because it doesn't have any color when the lights are turned out at night.

The terminology is NOT used differently in the diamond and gemstone world, since they are not two separate worlds when seen from a gemological perspective. Diamonds are a subset of colored stones and by their nature and low color saturations, can't show many of the features of darker colored stones. On the other hand diamonds can show the same dark areas which result from poor lighting conditions and one has to be careful that they are not calling reflections from dark areas "extinction" since this is not what's happening.

The difference is not between colored stones and diamonds or the terminology used, but in between good and poor lighting conditions used when determining a stones optical performance and whether it is showing extinction in all lighting conditions, (of which "head reflections" are part and is a constant cause of poor performance), or dark background reflections in poor lighting, (in which case the stone may be acceptable when the lighting improves).

 

[LD]

Absolutely 100% correct and this is why this thread is so confusing. The terminology is used differently in diamond world and coloured gemstone world!

Extinction = a gem cut with areas that do not return light - no matter what you do or how you look at it or where the light is/isn't.

This last sentence is THE reason for confusion. WHERE the light is or isn't, IS everything with any gem. Unless a gem has inclusions which distribute light evenly through the stone, or is fluorescent in which case light is produced evenly through the stone, any gem will show evidence of what people here call, "extinction", or dark areas in a gem. In many cases the dark areas being seen are due to poor lighting and are not a function of the cut of the stone or it's material properties. This is definitely a function of where the light is coming from and has nothing to do with the quality of cutting and little to do with the darkness of the material being used. I swear, one of these days I'm going to be reading that someone is not happy with the stone they've just bought because it doesn't have any color when the lights are turned out at night.

The terminology is NOT used differently in the diamond and gemstone world, since they are not two separate worlds when seen from a gemological perspective. Diamonds are a subset of colored stones and by their nature and low color saturations, can't show many of the features of darker colored stones. On the other hand diamonds can show the same dark areas which result from poor lighting conditions and one has to be careful that they are not calling reflections from dark areas "extinction" since this is not what's happening.

The difference is not between colored stones and diamonds or the terminology used, but in between good and poor lighting conditions used when determining a stones optical performance and whether it is showing extinction in all lighting conditions, (of which "head reflections" are part and is a constant cause of poor performance), or dark background reflections in poor lighting, (in which case the stone may be acceptable when the lighting improves).

I wish that were true. So is a bow-tie obstruction? You can see how confused I got in this thread - and it was purely down to terminology:

[URL='https://www.pricescope.com/community/threads/is-leakage-bad.131051/?hilit=extinction']https://www.pricescope.com/community/threads/is-leakage-bad.131051/?hilit=extinction[/URL]

Regardless of the words, I am now thoroughly confused and will respectfully bow out of this thread!

 

[packrat]

Ha, LD, I know how you feel! I read it and think ohhh ok, maybe, wait, nope, nevermind it's not clicking. I sent my ring to Michael to look at the at the stone for possible extinction, and reading his explanations, it was like I could grasp it for a second and then it was gone.

 

[LD]

Ha, LD, I know how you feel! I read it and think ohhh ok, maybe, wait, nope, nevermind it's not clicking. I sent my ring to Michael to look at the at the stone for possible extinction, and reading his explanations, it was like I could grasp it for a second and then it was gone.

We're obviously inhabiting the same world Packrat! It's good to know we're not alone!

 

[Michael_E]

So is a bow-tie obstruction?

If you're seeing a reflection of something dark and symmetrical across one of the main axes of symmetry of a light colored stone, diamonds included, then it is more than likely your head.

Regardless of the words, I am now thoroughly confused and will respectfully bow out of this thread!

My intention was to troll for a much more animated response from you LD, not to have you quit the thread.

This is much more simple than we are all making it out to be. Let's try this, a gem is basically a mirror with a prism in front of it. If you take a mirror and look at it, your reflection is usually the darkest thing in the mirror. It has nothing to do with obstructing anything, it's just your reflection.

Now, cut the mirror into two pieces and look into. With the right angles you will see two reflections of yourself. Cut it into more pie shaped pieces and arrange them into a circle...voila you now have a pavilion. With the right angles can reflect either your head as a dark circle in the mirrors or change the angles and you can see what's around your head.

Now imagine taking that cone of pie shaped mirrors and squishing it into an oval cone. Some angles will be steep and others shallower. Squish it just right and the angles on the sides will show you your head, which is dark, while the tops and bottoms of the oval set of mirrors will be showing you the ceiling and floor, which are lighter...voila you've got a "bowtie"shaped reflection. All this with just a set of mirrors and no "crown".

We can add a "crown" to our mirror gem by getting some big prisms and placing them over the mirrors, but then things get a little too complicated to imagine for most people. Even though we can't imagine it, it is still easy to see that the only things that can be reflected from a gem are what's in front of it. Some dark areas are reflections of your head, some are from dark areas around you, some are from the stone absorbing light or in a very poorly cut stone, from what are basically small windows in areas of the stone allowing you to see through the stone to dark areas behind and to the sides of the stone, (these "windows" are not always line of sight, but can be reflected windows).

From my point of view, the only dark areas in a gem which matter are those which detract from it's beauty under ALL lighting conditions. Those are the ones which I would consider "extinction" because they extinguish my interest in that stone, (O.K. they aren't the same thing, but you get the idea). In this case those dark areas are always caused by either "head reflection", too dark a stone absorbing light, a poor cut causing you to be seeing through the stone in some way or a combination of these things. Anything else is NOT extinction but reflections of dark areas in the light environment of the stone and so is temporary and not a concern. Let me know if that makes sense and if not I'll just keep blabbing on.

 

[Garry H (Cut Nut)]

So is a bow-tie obstruction?

If you're seeing a reflection of something dark and symmetrical across one of the main axes of symmetry of a light colored stone, diamonds included, then it is more than likely your head.

Regardless of the words, I am now thoroughly confused and will respectfully bow out of this thread!

My intention was to troll for a much more animated response from you LD, not to have you quit the thread.

This is much more simple than we are all making it out to be. Let's try this, a gem is basically a mirror with a prism in front of it. If you take a mirror and look at it, your reflection is usually the darkest thing in the mirror. It has nothing to do with obstructing anything, it's just your reflection.

Now, cut the mirror into two pieces and look into. With the right angles you will see two reflections of yourself. Cut it into more pie shaped pieces and arrange them into a circle...voila you now have a pavilion. With the right angles can reflect either your head as a dark circle in the mirrors or change the angles and you can see what's around your head.

Now imagine taking that cone of pie shaped mirrors and squishing it into an oval cone. Some angles will be steep and others shallower. Squish it just right and the angles on the sides will show you your head, which is dark, while the tops and bottoms of the oval set of mirrors will be showing you the ceiling and floor, which are lighter...voila you've got a "bowtie"shaped reflection. All this with just a set of mirrors and no "crown".

We can add a "crown" to our mirror gem by getting some big prisms and placing them over the mirrors, but then things get a little too complicated to imagine for most people. Even though we can't imagine it, it is still easy to see that the only things that can be reflected from a gem are what's in front of it. Some dark areas are reflections of your head, some are from dark areas around you, some are from the stone absorbing light or in a very poorly cut stone, from what are basically small windows in areas of the stone allowing you to see through the stone to dark areas behind and to the sides of the stone, (these "windows" are not always line of sight, but can be reflected windows).

From my point of view, the only dark areas in a gem which matter are those which detract from it's beauty under ALL lighting conditions. Those are the ones which I would consider "extinction" because they extinguish my interest in that stone, (O.K. they aren't the same thing, but you get the idea). In this case those dark areas are always caused by either "head reflection", too dark a stone absorbing light, a poor cut causing you to be seeing through the stone in some way or a combination of these things. Anything else is NOT extinction but reflections of dark areas in the light environment of the stone and so is temporary and not a concern. Let me know if that makes sense and if not I'll just keep blabbing on.

Hi Michael,
All the diamond people agree that some extinction caused by head obstruction is essential. Pure light return, like a head lamp, is unintersting.
A checker board has half the light return of white paper, but is many times more brilliant.

What started me on this was Richard's article.
I hope the meandering trail has provided some enlightenment, and I invite Richard to pop in for some discussion since he is an influential player.
I would like to discuss his Figure 1 where he is correct - that in many instances light could return to the observers eye. But his schematic skecth is woeful and inaccurate.
Rays that arrive perpendicular to an observer in RI 1.5 enter a 43 degree prism at about 12 degrees away - not as represented.
As represented there would clearly be extinction because of head obstruction, obscuration of illumination or whatever folk wish to call it.

I think part of the blame may lay with GIA's early lectures for some of these misunderstandings. Had they only fully understood Bruce's work then a whole different level of diamond and gem cutting could have started much earlier.

I have asked one of my staff to can a couple of pale sapphires so I can show what some causes of extinction actually are.
If someone has absorption spectrum to add to the scans that would be great - pale and dark material

 

[Garry H (Cut Nut)]

PS for Richard's sketch to be valid the angle must be 45 degrees

 

[beryl]

. Garry: As you say, the illustration would be correct only if the pavilion slope was 45°. It was this illustration which made the entire article suspect to me.
. The divergence between the two 'vertical' internal rays is 4 times the difference between the pavilion slope and 45°. Hence, in this case it would be 4x(45°-43°)=8°- the angle on the right in the stone of your diagram; this is independent of RI. The external divergence is even greater because one or both rays are bent by refraction at the crown; that IS dependent on RI = 19.6° for diamond or 12.3° for quartz at the right ray external to your stone.
. Your diagram includes the entry loss by reflectance, which is 17.2% for diamond, but only 4.7% for quartz. Your diagram shows only 4% - for what material (hyalite opal?)? I have recently made Excel reflectance charts for the 8 RI's shown in the article "Faceting Limits". They can also be used to calculate the reflectance for other materials at whatever angles of incidence the user enters. You or some of the readers might want copies.

 

[Garry H (Cut Nut)]

. Garry: As you say, the illustration would be correct only if the pavilion slope was 45°. It was this illustration which made the entire article suspect to me.
. The divergence between the two 'vertical' internal rays is 4 times the difference between the pavilion slope and 45°. Hence, in this case it would be 4x(45°-43°)=8°- the angle on the right in your diagram. This is independent of RI. The external divergence is even greater because one or both rays are bent by refraction at the crown; that IS dependent on RI = 19.6° for diamond or 12.3° for quartz.
. Your diagram includes the entry loss by reflectance, which is 17.2% for diamond, but only 4.7% for quartz. Your diagram shows only 4% - for what material (hyalite opal?)? I have recently made Excel reflectance charts for the 8 RI's shown in the article "Faceting Limits". They can also be used to calculate the reflectance for other materials at whatever angles of incidence the user enters. You or some of the readers might want copies.

I used 1.5 because that was what Richard quoted Bruce. So the Diamcalc #'s are accurate
Thanks for doing the math (or is that arithmetic?).

 

[Garry H (Cut Nut)]

I think this series of photo's is self explanatiory?
The piece of white card infront of the camera in one of the photo's has a 8.5mm hole cut in it and the front of the lens is about 42mm from the stone in both photo's.
I could make this extinction a lot darker by putting a black card infront of the silver camera (which has a dark lens of just 15mm).

If anyone needs more proof I also have a 3D Helium scan of the 1.22ct Sri Lankan Sapphire.

Anyone can easily replicate this experiment.

 

[beryl]

Garry: I don't recognize any of the apparatus in the photos except for some wires. Can you add labels to one of the photos?

 

[Garry H (Cut Nut)]

Garry: I don't recognize any of the apparatus in the photos except for some wires. Can you add labels to one of the photos?

 

[beryl]

Thank you, Garry. I was even wrong about the 'wires', but I'll bet that the little blue thing is the sapphire.
. When I did jewelry repair (70's) I made before-and-after photos using a close-up dental camera and had the camera-image problem on the polished metal (I was unaware of the gem obstruction problem then). A professional photographer showed me the hole-in-paper trick. For jewelry advertizing photos he made a conical tent of translucent Mylar with a fluorescent halo light around it and a small hole in the side for the camera to see thru. I realize now that he must have lost the pleasing contrast which results from obstruction.
. I heard that, to avoid reflections, Smith & Wesson (a nearby gun manufacturer) had a white chamber with angular non-reflecting walls and a camera peep-hole to make their advertizing photos; however, they were not affected by light-source obstruction since they have no internal reflections.

 

[beryl]

. This illustration shows only bezel-to-table rays coming to each eye of a viewer and how they move as the stone is tilted. Note how many of the rays are blocked by his head. This is an 'ideal' diamond with 34.5° bezel, 40.75° pavilion and 53% table

 

[Garry H (Cut Nut)]

Bump?
It seems that you all went very quiet all of a sudden.

Surely there is a lot of useful information here that can result in better cutting and better selection?
My greatest learning has come from when somone showed me something that changed my opinion about some assumed fact.

Based on many comments from page 1 and 2 of this discussion it would seem the photo's I have posted and the pearls from Beryl should be rather convincing?

If I am mistaken about some part, or there are other possabilities, then please show me how or where so I can learn more.

 

[FrekeChild]

It seems to me that the only purpose this thread serves at this point is as an echo chamber for you and beryl, Garry. I don't mean any disrespect, but I think that you are preaching to the wrong crowd and I really can't imagine why you started this thread in CS. I personally wish you had stayed in Rocky Talky with your diamonds and their light performance.

If you actually spent time in here (I don't think I've ever seen you post in here before and I've been around pretty much constantly for the past 3+ years) you'd find out that cut is NOT king in CS, and COLOR is king. You've been telling a whole bunch of people they don't know what they are talking about, and frankly I was happy to see this thread dying.

I have seen a stone look dark because my head is blocking the light. I have seen stones (ovals specifically) that were cut in a way that I would have to move the stone so that light would hit one side...but wouldn't hit the other. One side would be lit up and the other would black out (what we call half and half extinction). I have seen that same stone with two light sources--natural hitting one side and incandescent hitting the other side--which was very very cool in a color shifting stone, but a very rare occurrence. I have seen stones that are black--and not due to body color. I have seen tilt windows. I have seen bowties. I have seen stones that are windowed. I have seen stones that are cut amazingly badly and I've seen stones that are cut amazingly.

Regardless, color is king. If it's decently cut, great, but its the color that talks over here. Many many many people will take a stone that is an amazing color and cut that is lacking over a stone that is perfectly cut and a moderate color. I'm really only seeing a bunch of rhetoric about diamond angle cutting...and how gemstones are the same thing.

No. They aren't. One is usually white, and the other is any color in the rainbow.

Diamonds are a dime a dozen (figuratively), and each individual stone here is special. No matter what it's cut.

People over here buy what they like. People over here don't want to walk around with white paper taped to their foreheads. People over here aren't looking at light return. They are looking for COLOR.

And really Garry, I know that light performance is your "thing" but you could at least listen to what the people you are preaching to are saying. And as usual, you aren't.

 

[Michael_E]

Surely there is a lot of useful information here that can result in better cutting and better selection?
My greatest learning has come from when somone showed me something that changed my opinion about some assumed fact.

Based on many comments from page 1 and 2 of this discussion it would seem the photo's I have posted and the pearls from Beryl should be rather convincing?

If I am mistaken about some part, or there are other possabilities, then please show me how or where so I can learn more.

Well, I for one, am listening. The problem with much of what you and Beryl have been saying is that it is not immediately applicable. The reason is that colored stones span a wide range of refractive indices, as well as depths of color, with darker stones absorbing light more and often in non-linear ways as light is transmitted along different axes of the crystals being cut. When cutting these stones a person also has to take into account the different aspect ratios, since most colored gems are not cut as rounds. All of this requires more involved modeling analysis in order to get the best looking stone possible while maintaining as much of the original weight as possible. While diamonds are a lot more time consuming to cut, I would have to say that cutting non-round colored gems takes far more planning and modeling.

You also have a problem on this particular section of this forum in that many of the participants don't "get it" and don't want to "get it". Those that do and those that don't all still fall into the same category of being unable to use any of this, because they aren't cutters and don't have the ability or desire to analyze the details of the stones they are buying...they just want the colors to be vibrant and the cuts to be good enough so that they can talk about them without someone picking them apart. I'm not sure why FrekeChild is chewing on you, maybe she needs a tropical vacation or a stiff drink.

I think that if you want to have a continuing discussion about the intricate details of colored stone cutting, you may be better off taking it to the lapidary section of Gemology Online. The downside is that most cutters don't want to bother with the details of design either, they just want to grab a design that works for the rough they have and cut it. I do like the ideas that you guy's have been discussing and am going to continue to use these ideas in my designs and modeling, (not that it's going anywhere, but it is interesting and produces some novel cut ideas which are fun to play with).

 

[movie zombie]

yes, this discussion is more appropriate for cutters.

MoZo

ps i don't care what you call it or how it gets there, i don't like "extiniction". the better the rough, the better the cutter, the better the cut certainly means less of it. but most here aren't willing to pay the $ necessary to avoid it. and those of us that it bothers, well, we have limited color stone collections.

 

[FrekeChild]

No, FrekeChild just remembers a certain thread about BGD a little too well and that impression (and the others made by Garry before that particular trainwreck) has stuck with her.

Now that I'm done talking about myself in 3rd person...

For what it's worth, Michael, I have found your posts to be very informative and interesting. My husband has been considering taking up cutting as a hobby, and seeing as how he is terribly geeky in the math realm, I can see how all of this would interest him. Frankly, so long as it sparkles, it's fine with me. And I'm perfectly happy letting everyone else figure out how to make a particular piece of rock sing.

Just make sure it's a decent color first.

 

[Garry H (Cut Nut)]

And really Garry, I know that light performance is your "thing" but you could at least listen to what the people you are preaching to are saying. And as usual, you aren't.

Correct FC.
And my motivation is change - to change for the better. I have listened and so far there has been not much peer discussion.

Most has focused on diamonds being different. The only common difference is that most fancy colored diamonds are very light and we need to make the color more saturated trhough the cutting, but not by head obstruction.
The same techniques work both ways.

Please consider this work and other articles and material in the menu to the left:
http://www.octonus.com/oct/projects/modeling.phtml
Starting like this:


Sergey Sivovolenko, OctoNus
Yuri Shelementiev, Moscow State University Gemological Center
Roman Serov, Moscow State University Gemological Center

1. Computer modeling of gemstones
2. Discussion
3. Technology applications
4. Conclusion
5. Literature and data sources

Computer modeling of gemstones

There are many cases when a better cut can reveal a better color of a gemstone, and many cases when a gemstone’s appearance has some flaws because of its cut. Unlike diamond, colored gemstones cutting allows for a lot more freedom. A cutter can choose among many shapes, facet patterns and proportion sets. The primary goal for a cutter is to achieve the best possible color and to reveal the potential of every piece of rough material. Because of the complicated nature of interaction between light and gemstone facets, every facet matters. Cutting mistakes can become evident only after the last facet is polished. Today many commercially available colored stones have various optical flaws in their appearance. That is why cutters are looking for a way to predict the optimal appearance of future gemstone’s.

Recent advances in diamond scanning technologies have introduced computer 3d models of diamonds. There are Sarin, OGI, and OctoNus scanners commercially available. The same technology can be used for colored stones as well. Libraries of 3D cuts are available now on the Internet for free. Another type of 3D cuts is parametrical cuts that can be opened in software products such as DiamCalc by OctoNus or GemCad by Robert Strickland. These cuts are parametrical: they are symmetrical and determined by a set of parameters. Modern software products, for example DiamCalc, can model gemstones of a particular color if a user imports an absorption spectrum. This spectrum can easily be recorded with a conventional visible range spectrometer or obtained from an Internet database.

The described technology combines gemstones absorption spectra and 3D modeling for predicting the color appearance of gemstones before their cutting and polishing. A recorded spectrum should be adjusted in order to avoid all light losses and calculating an absorption coefficient, especially if this spectrum is not recorded through two parallel windows. To properly simulate a colored gemstone image on a computer screen a software product should model not only stone itself, but also illumination and should also take into account properties of human vision. Every cut can be characterized by its size, shape, facet arrangement, proportion set, and symmetry deviation. Every gemstone material is characterized not only its spectrum but also refraction indexes and dispersion that should be incorporated in the model. DiamCalc software creates rendered gemstones images by tracing all light beams that come from light sources through a gemstone to an observer’s eye, and calculates the color of every virtual facet, dependant on the path of light rays and material absorption. Parametrical or scanned cuts can play the role of the gemstone.

The resulting images provide a lot of valuable information. Color appearance changes with size, shape, facet arrangement, cut proportions, distance, illumination, background, stone’s position, and viewing conditions. On the Figure. 1 one can see pairs of DiamCalc images. In each pair the gem material is fixed, but one model in each pair is less attractive while the other has better look. The reasons are explained in captions and every example illustrates how to improve a gemstones appearance by computer modeling.

 

[Garry H (Cut Nut)]

Firstly thanks Michael

Well, I for one, am listening. The problem with much of what you and Beryl have been saying is that it is not immediately applicable. The reason is that colored stones span a wide range of refractive indices, as well as depths of color, with darker stones absorbing light more and often in non-linear ways as light is transmitted along different axes of the crystals being cut. When cutting these stones a person also has to take into account the different aspect ratios, since most colored gems are not cut as rounds. All of this requires more involved modeling analysis in order to get the best looking stone possible while maintaining as much of the original weight as possible. While diamonds are a lot more time consuming to cut, I would have to say that cutting non-round colored gems takes far more planning and modeling.

It is true that many gems are pleochroic. Weighht retention is a big issue and I would hope that we can educate consumers to demand and use measures of spread the way that is common in diamond world. Weight retention is one very large aspect of the extinction problem in my view when we speak about darker material.
However planning and polishing fancy colored diamonds involves a lot more consideration and more science and trial and error type experiance is employed than any applied in the coloured gem world (in my experiance apart from concave faceting.)

You also have a problem on this particular section of this forum in that many of the participants don't "get it" and don't want to "get it". Those that do and those that don't all still fall into the same category of being unable to use any of this, because they aren't cutters and don't have the ability or desire to analyze the details of the stones they are buying...they just want the colors to be vibrant and the cuts to be good enough so that they can talk about them without someone picking them apart. I'm not sure why FrekeChild is chewing on you, maybe she needs a tropical vacation or a stiff drink.

I guess one of my aims and goals in this discussion is eactly that - to educate consumers. Note that FrekeChild's hubby could have the technical background and be the type of person who becomes a consumer expert as so many have in Rocky Talky. My experiance on Pricescope is that it is often easier to educate consumers than tradespeople.

I think that if you want to have a continuing discussion about the intricate details of colored stone cutting, you may be better off taking it to the lapidary section of Gemology Online. The downside is that most cutters don't want to bother with the details of design either, they just want to grab a design that works for the rough they have and cut it. I do like the ideas that you guy's have been discussing and am going to continue to use these ideas in my designs and modeling, (not that it's going anywhere, but it is interesting and produces some novel cut ideas which are fun to play with).

Thanks again, and it is great to know that you may have found some info that will help you in your business and make better use of the scarce commodity of gem rough. My initial and ongoing involvement with Pricescope has partially been driven by the knowledge that changing consumer demand thru consumer education has a huge impact on supply through higher standards of demand. Some people think our contribution on Pricescope has led to an improvement in diamond quality. I believe that is true. In the future I would hope we can do much more for fancy shape and fancy colored diamonds. And all other gems!

 

[FrekeChild]

And really Garry, I know that light performance is your "thing" but you could at least listen to what the people you are preaching to are saying. And as usual, you aren't.

Correct FC.
And my motivation is change - to change for the better. I have listened and so far there has been not much peer discussion.

At least Michael gets it.

You aren't here talking to cutters or math nerds Garry, but to CONSUMERS. Consumers that often have set criteria that they buy from. Most of them want a "decent" cut with no window and no black reflections, and they want color.

What is the end result that you are desiring out of this thread? I'm just curious.

You aren't going to change Joe Bob Newb's mind about a big green sapphire that he just wants to be pretty to give to his fiancee. You aren't going to change Jane Collector's mind about it if she's after the most highly sought colors. You might catch the attention of John Cutter, who is interested in selling more stones/making his product better.

But honestly, this is a very consumer based part of the forum (Michael, nail, head, you know the drill). A vast majority of the posters here are here to buy stones. To learn how to buy something pretty and get the most for their money.

When I buy a gemstone I am paying for:
1. Someone that has the color rough I want my gemstone to be.
2. Someone that is honest and discloses treatment, etc.
3. Someone that has a lapidary machine.
4. Someone that cuts rocks into gems and makes them sparkle.
5. Someone who wants to figure out how to not get windows, bowties, minimize tilt windows, minimize half and half extinction, etc in the material I am paying for, and leave me to admire the beautiful item they have made out of a rock.

I, as a consumer, am paying for someone else to read about this stuff and make it happen with their cutting skills so I can buy it.

Perhaps Gemology Online would be a better playground for this discussion, but it seems counterproductive to post on a competing forum, especially given your investment in PS...even though it is far more technical and less consumer based. Which is what you're striving to achieve with this thread, is it not?

Or is it? Forgive me, I don't get it.

For the record, if anything, my husband would likely become a member of the trade, never step foot in Rocky Talky, and likely never on PS. Way too much drama, he says...

 

[Garry H (Cut Nut)]

If you actually spent time in here (I don't think I've ever seen you post in here before and I've been around pretty much constantly for the past 3+ years)

https://www.pricescope.com/community/search/
Seems I have posted a fair bit in here FC

 

[FrekeChild]

Pardon me, but 6 threads is not terribly impressive to me, when more than half (quite a bit more than half) of my 15,000+ posts have been in Colored Stones, and it appears to be the only part of PS I care to visit anymore.

I, too, am leaving this thread now, as it is going nowhere I'd like to go.

 

[chrono]

This discussion has morphed into trying to find the perfect angle(s) which most posters here aren’t lapidaries, hence seeming lack of participation. We have limited to no input to the lapidary on how to best facet a particular piece of rough and in any case, many do not have the knowledge or do not care to acquire such knowledge because of the amount of depth of involvement required. There are too many variables as it is in trying to decide on the best usage of the rough (choosing the correct axis, working with or around cleavages and other characteristics like brittleness and inclusions specific to that particular gem variety, refractive index, tone of the rough, shape of rough to maximize yield and more), much less decide on a specific cut pattern or design. It is this very large range of considerations that makes it almost impossible to create that set of perfect angles for that specific gem type. This perfect angle cutting model is more easily applied to colourless or white diamonds for the simple reason that there is no colour consideration at all (other than to decrease the impact of colour).

While it is true that spread IS important in the coloured gemstone world, colour still comes first. Sometimes, spread is sacrificed in order to get a better saturated stone because a longer light path can mean better saturation for lighter toned material. However, from a buyer’s perspective, we usually avoid depths of over 75% because we don’t want to pay for that depth that we do not see face up.

 

[beryl]

Garry:
. You started this thread to correct misinformation these folks had received elsewhere.
. Like Don Quixote, you have been jousting at windmills.

 

[Aoife]

Garry:
. You started this thread to correct misinformation these folks had received elsewhere.
. Like Don Quixote, you have been jousting at windmills.

The discussion has been very interesting, and I've especially appreciated the participation of PS'ers who are in the trade, as well as those CS regulars who generously share their knowledge from a collector's viewpoint. However, aside from that, I'm a bit puzzled as to what additional kind of discussion Garry and Beryl were hoping for. And frankly, this last comment by Beryl seems more likely to shut down discussion than invigorate it.

Just speaking as one of those swine before whom these pearls of wisdom have been cast.

 

[LD]

Thank you Freke for saying what I didn't have the guts to say.

I don't give a rat's bum if a gem is cut well if the colour isn't there in the first place.

As Freke has said, colour is king not cut in our part of the world! Cut is not what coloured gemstones are about - hence the total lack of interest from this side of the forum. Generally speaking the normal consumers on this side of the fence are not the least bit interested in light performance or math!

 

[Arcadian]

I have to admit I saw this thread, read some of it, and it made my head hurt.

I DO have an appreciation for well cut stones of the colored variety, but my main focus is the color. Cut can help me like a stone where color is lacking, but on the real, if that color is all there, cut? what cut? lol man I will take the stone as long as that color is there 4-real!!(thats not a lie either, I got some stones to back that up! )

Many of us tend to focus on treatments because thats what affects us the most. I'm not saying that cut dosen't because it has bearing, if you're taking about a sapphire thats nuked to hell and back with a great cut and a sapphire that has awesome color but a so so cut, guess which one most people here would buy.

To that end, Gary, I think it all starts with babysteps. Outside of the colors of the stones, Treatments are really the number 1 concern for a lot of us because those treatments can and do affect the colors of the stones sometimes. They certainly can make or break the value of them thats for sure! So I know I don't speak only for myself when I say I would LOVE to see more info treatments and how they're tested for in one space instead of it being spread to the far corners of the internet. If Pricescope had such a resource it would really rock!

And yes as much as I would love for some of my stones to not go dark in certain lights, thats the way it is. I have accepted pretty much as inevitable. The rest of the convo went so far over my head I can't even follow it.

Ok Imma shut up now...lol

-A

 

[Michael_E]

Cut is not what coloured gemstones are about - hence the total lack of interest from this side of the forum. Generally speaking the normal consumers on this side of the fence are not the least bit interested in light performance or math!

Well that depends LD. Many of the consumers on this forum are not in a position to purchase stones in which the color is SO GOOD that the cut doesn't matter. With some of the fluorescent spinels and rubies which have been posted here recently, as well as the electric colors of some blue and green tourmalines, the cut of the stone really has little to do with how the color is presented in the stone, this is because the material itself does actually glow and has light distributed from all parts of the stone by fluorescence and micro inclusions.

With much lower valued stones that do not have such grand internal properties, the cut is what brings the color out in the stone and makes it what it is. In that regard the cut is everything, since without it you can end up with a "black hole". The really odd thing to me is why people here are so focused on only the very best materials and NOT on good cutting which can make modest materials look much better. It seems to be either "all or nothing here" instead of a more thoughtful and perceptive position of people becoming more astute in their perceptions of some gems which are attractive in their price points and with certain reservations about where they can be worn effectively. Cutting to minimize extinction is critical in many stones where excess extinction is visual death to that stone. Recognizing when you're actually looking at extinction or are just in the wrong lighting environment, is also critical when buying lower valued stones which may be acceptable to their owners in a different environment.