A good native cut for retaining color ?

[arjunajane]

Date: 10/17/2009 2:45:08 AM
Author: morecarats
I've already expressed my opinions on the interesting brilliance vs. color debate. There are are some gemstone cuts that I don't find appealing, but I am happy to sell them if people want to buy them. Concave cuts are currently a good seller with us, but I would not likely buy one myself. My opinions are not based on commercial considerations, though I'm always happier if customers buy something which is right and beautiful. But fads are part of the fashion world.


I don't own or run a jewelry store.


Can we return to discussing colored stones?

well, more carats you are the one that continues to post referring to what gems you sell, your customers, "what the buyer wants" and other terms such as these.
Ok, you don't run a store, you run a site, or whatever, it's semantics.

If you would like to return to solely discussing coloured stones, and not your business motivations - perhaps don't pepper your posts so much with references to your business.?

Just a suggestion.

 

[chrono]

Date: 10/16/2009 11:38:52 PM
Author: Gailey

Date: 10/16/2009 12:07:44 PM

Author: arjunajane

Date: 10/16/2009 9:15:59 AM

Author: morecarats

Arjunajane, I'm with you in feeling uncomfortable with gems that look too manufactured. I know some people really love concave cuts, and they can look very impressive in larger stones, especially lighter colored ones. But you rarely see a fine sapphire or ruby in concave cut. I have seen some large concave cut fluorites that showed very interesting patterns through the table from the concave facets. Some people think they look a bit plastic, but they have been popular in the market.

Hi MC, well I think precision concave faceting and the Chinese factories you referred to are 2 completely different animals to start with and not really comparable!

But I am in agreement with you re. concave faceting in general - it is not my personal cup of tea as I prefer traditional faceting. But each to their own.

Btw, Richard Homer is known for cutting valuable/larger stones such as blue and pink sapphires in his concave cuts.


Oh, and I think someone asked you in another thread - but usually when you are part of the trade, it is polite to designate this in your signature.

Yes AJ, that would have been me. And it's not only polite, it's policy. Now I will state up front (because that's the kind of girl I am) that I won't report Morecarats for this infraction, but you can bet your bottom dollar someone will before long.


And that would be a shame. I spent some time reading through Morecarat's posts since he/she joined us and for the most part they are very informative, so it will be a shame to lose him/her.

Gailey,
Perhaps I am incorrect but is it really the policy? Prior to the Octavia, no one knew who Diagem was other than he was in the trade as well (except for the regulars who knew he's a diamond cutter). I do not recall him even adding a signature.

I have no issues with Morecarats wishing to remain anonymous. He has not linked to any stones or store, and never pushed or recommended any products, therefore why would it matter if he's in the business of selling / cutting gemstones? His advice all appear to be unbiased and very informational.

 

[colormyworld]

from the link Harriet posted. Quote by Finewatergems.

"As a fairly new cutter, I had bought into the idea that "precision" cutting was always superior to "native" cuts. That is, until I bought some nice blue zircons last year in Chanthaburi, Thailand. They were actually well cut, but I thought that I could improve them by recutting. I was shocked to find out that recutting did not really help. The brilliance was improved, but the color was less saturated. It was a humbling realization that maybe these cutters know what they are doing (they've only been doing this for hundreds of years!) "

 

[Gailey]

Date: 10/17/2009 7:56:18 AM
Author: Chrono

Date: 10/16/2009 11:38:52 PM
Author: Gailey

Gailey,
Perhaps I am incorrect but is it really the policy? Prior to the Octavia, no one knew who Diagem was other than he was in the trade as well (except for the regulars who knew he''s a diamond cutter). I do not recall him even adding a signature.

I have no issues with Morecarats wishing to remain anonymous. He has not linked to any stones or store, and never pushed or recommended any products, therefore why would it matter if he''s in the business of selling / cutting gemstones? His advice all appear to be unbiased and very informational.

Respectfully snipped

Good morning Chrono
After I read your post I went back and took a second look at the policy. Here''s what it says for Trade members:

Members of the diamond and jewelry trade must identify themselves by specifying their personal and business names in their profiles.

I guess this means Morecarats is correct if he doesn''t sell diamonds or jewellery and only sells coloured stones. I stand corrected and therefore apologise to Morecarats for suggesting he was in breach of policy. Can''t help thinking it''s a pretty fine line however. I guess I am just used to the other coloured stone suppliers that post being completely up-front with who they are. I''m a pretty WYSIWYG kind of person and assume others to be also. Perhaps I ought not make such assumptions

I always assumed that Diagem remained anonymous because he didn''t sell directly to the consumer. Dammned shame because I should have loved some of those french cut traps he does so beautifully.

However, I digress. So Morecarats becomes our new international man of mystery, fair enough.

 

[psadmin]

Just to clarify the policy means that diamond/colored stones/jewelry trade needs to let the admin/moderators know who they are. The best way is to do it via the profile. It also helps us keep everything fair on the forum.

A trade member has a choice to use the signature part to let others members no who they are. In our opinion, this is in there best interest as it gives them credibility and a way for consumer to contact them if they wish.

I hope this helps.

 

[PrecisionGem]

This thread is filled with half truths, non valid arguments, bias and romantic sales pitches.

To make any comparison of cutting, you must have the same material to start with, and the same size. To simply the syntax, lets use the term "Native cut" to mean it''s common usage as a not so well cut, possibly windowed, non symmetrical, poor meets etc., and a "precision cut" to be a stone cut on a modern faceting machine by an experienced cutter.

It seems that many are thinking that a precision cutter is somehow not able to maximize the color of a stone, but only make a stone brilliant and not window. But that the native cutter, since he has been doing this since the bronze age (must be a really old cutter), can maximize the color of a stone, there fore a more valuable stone, since color is king. Now wouldn''t you think that the precision cutter realizes that color is important, he also has 1000''s of designs that people before him have worked out, plus modern tools that allow him to model stones in 3D on the computer, ray trace them, produce diagrams with dispersion and brightness could figure this out? Not to mention, you could reverse engineer a stone from one of these native cutters. So why not take one of these native cut stones, and duplicate it with a much higher grade polish and meet points that meet?

Could it be that you are comparing a really good color stone, with not so good cutting to less quality color wise stone? Another thing, not all stones just because they are "precision cut" are the right cut for the stone, or even cut to the correct angles. They may have a great polish, and good meets however.

Recutting is another thing. Any time you recut a stone, it has to get smaller. Anytime a material is smaller, the perceived color, all other things being equal will have a lighter tone. Take a drop of Windex and put it on a white plate, it looks almost colorless, while the whole bottle is a deep blue. So comparing a re-cut to the original, the recut is already at the size disadvantage, and this can at times be made up for in the cut. This would be a function of the stone, and the original cut you are comparing it to.

The only fair comparison would be to take identical material, and have them cut. I would venture to say that 1 piece of lab created sapphire was cut into four 15 ct. pieces, and one piece give to a certain famous concave cutter, one given to a famous fantasy cutter, another given to an experianced "precision" cutter, and the other sent to a Thailand cutting house, the first 3 would sell for a lot more than the last one, and almost no one on Pricescope would pick the Thai stone over the others.

Just because a region has been doing something since hundreds or thousands of years, doesn''t mean it''s done right. The Masai tribal "doctors" in Africa have circumcising boys and girls for a long time in the bush, if it was me having do today, I''d much rather take my chances in a western style hospital.

 

[PrecisionGem]

I found this sapphire, that looks to be "native cut". The website was kind enough to offer a 3d scanned image of the stone along with the angles of each facet. From this I was able to model the stone in the software I use to create gem designs. Since the cutting was pretty inconsistent and the stone not symmetrical, I had to average a each facet tier. So here''s the 3d scan of the stone

 

[PrecisionGem]

Here''s my model of the above cut stone.

 

[PrecisionGem]

Now if I were to cut the stone as a standard round, here would be one cut that could be used. This is a pretty standard round design, used by cutters all over the world. Commonly refereed to as a SRB or Standard Round Brilliant. Usually cutters will adjust the angles a bit depending on the material, or may change the difference in the pavilion facet angle 1 and 2 a bit. A larger difference in angle of these two facets can give the stone that "chunky" look you read about on pricescope so often.

 

[T L]

Date: 10/17/2009 3:03:40 PM
Author: PrecisionGem
This thread is filled with half truths, non valid arguments, bias and romantic sales pitches.

To make any comparison of cutting, you must have the same material to start with, and the same size. To simply the syntax, lets use the term 'Native cut' to mean it's common usage as a not so well cut, possibly windowed, non symmetrical, poor meets etc., and a 'precision cut' to be a stone cut on a modern faceting machine by an experienced cutter.

It seems that many are thinking that a precision cutter is somehow not able to maximize the color of a stone, but only make a stone brilliant and not window. But that the native cutter, since he has been doing this since the bronze age (must be a really old cutter), can maximize the color of a stone, there fore a more valuable stone, since color is king. Now wouldn't you think that the precision cutter realizes that color is important, he also has 1000's of designs that people before him have worked out, plus modern tools that allow him to model stones in 3D on the computer, ray trace them, produce diagrams with dispersion and brightness could figure this out? Not to mention, you could reverse engineer a stone from one of these native cutters. So why not take one of these native cut stones, and duplicate it with a much higher grade polish and meet points that meet?

Could it be that you are comparing a really good color stone, with not so good cutting to less quality color wise stone? Another thing, not all stones just because they are 'precision cut' are the right cut for the stone, or even cut to the correct angles. They may have a great polish, and good meets however.

Recutting is another thing. Any time you recut a stone, it has to get smaller. Anytime a material is smaller, the perceived color, all other things being equal will have a lighter tone. Take a drop of Windex and put it on a white plate, it looks almost colorless, while the whole bottle is a deep blue. So comparing a re-cut to the original, the recut is already at the size disadvantage, and this can at times be made up for in the cut. This would be a function of the stone, and the original cut you are comparing it to.

The only fair comparison would be to take identical material, and have them cut. I would venture to say that 1 piece of lab created sapphire was cut into four 15 ct. pieces, and one piece give to a certain famous concave cutter, one given to a famous fantasy cutter, another given to an experianced 'precision' cutter, and the other sent to a Thailand cutting house, the first 3 would sell for a lot more than the last one, and almost no one on Pricescope would pick the Thai stone over the others.

Just because a region has been doing something since hundreds or thousands of years, doesn't mean it's done right. The Masai tribal 'doctors' in Africa have circumcising boys and girls for a long time in the bush, if it was me having do today, I'd much rather take my chances in a western style hospital.

I think that's my biggest issue with some, not all, precision cut stones. I do think that many native cutters do know their material very welll (cutting it over an over again), and do a better job retaining color than a precision cutter with less experience of such a gem species. For example, some garnets can go extinct if not cut properly, even if precision cut. Therefore, I'm glad you did admit that not all precision cut stones are the right cut for a particular stone, and I think that's what many people have a problem with when it comes to precision cut gems vs native cut ones.

 

[PrecisionGem]

You will notice that the last line of text has a formula on it. This is used to calculate the weight of the stone based on the width.

How this works is you take this number, in the case of the SRB its 0.212 an use it in this formula.

Wt in Cts. = Vol/W^3 x W^3 *0.005 x SG

Where SG is the Specific Gravity of the stone, and W is the width. Assuming we have a 10 mm sapphire we can calculate the weights.

So for the native cut stone it would be:

Ct Wt. = .230 x 10^3 x .005 x 4.1
Ct. Wt = 4.715 ct.

For the SRB precision cut it would be:

Ct. Wt. =.212 x 10^3 x 0.005 x 4.1
Ct. Wt = 4.346 ct.

 

[PrecisionGem]

Now for the Stats on the cuts.

FIrst the native cut stone. This is a copy of the Ray Trace. The very dark area is an area of either window, or extinction. You can see that the whole center area is windowed, and the brightness of the stone is 56.8% light return.

 

[PrecisionGem]

Now here is the "precision cut" SRB. Notice no window and the light return is 90.4%

 

[PrecisionGem]

And here is the stone tilted at 15 degrees. First the Native stone with a light return of only 66.9%

 

[PrecisionGem]

And now the precision cut stone with a light return of 77.1% and much less windowing.

 

[PrecisionGem]

So, why was the native cut done the way it was? I can''t answer that, but can provide a few possible reasons.

1. This is they the cutter was taught to cut for the last 500 years.
2. His equipment is primitive, and he really can''t do any better.
3. He needs to cut 30 stones a day or he will get fired.
4. The stone was shallow so he cut a fat belly to maintain weight despite the shallow stone.
5. He wanted to give the Pricescope people something to talk about.

Lets pick answer 4 and explore that. If we take the cutting diagrams and assume that the native cutter got every last bit of depth out of the stone, then the SRB couldn''t fit into the same stone and still be 10 mm. This can be seen by looking at the depth C and P and adding them up. For the native cut stone they = 5.613 mm and for the SRB they are 6.14 mm. So the SRB is deeper (and most likely better color since it is deeper).

THis means to fit the same depth stone with the SRB design we need a stone who''s diameter is only 9.14 mm and not 10 mm. Which then means the stone would weigh 3.32 cts.

In conclusion, the native cutter may have gotten a larger stone in both diameter and weight. But his stone has a large window, a greater tilt window. If the stone wasn''t shallow, then his stone would be the same diameter as the SRB, and only .369 cts more weight. I would think that the SRB would be a much more attractive stone, and even though it weighed a bit less sell for a higher price.

 

[PrecisionGem]

A photo of the native cut stone used in the above example.

 

[beaujolais]

I tell you - what a great thread. I''ve, once more, learned lots.

Thanks Dear Knowledgeable Friends.

 

[LadyBlue]

For stones like emeralds, saphires and rubies I love native cuts. For me precision cut in stones like emeralds, saphires and rubies just look cheap. While native cuts seem so fancy

, well that just me taste

 

[morecarats]

Date: 10/17/2009 9:19:15 PM
Author: gaby06
For stones like emeralds, saphires and rubies I love native cuts. For me precision cut in stones like emeralds, saphires and rubies just look cheap. While native cuts seem so fancy

, well that just me taste

Gaby06, please don''t confuse the cutting style (step cut, brilliant cut, etc.) with the cutting method. Simple elegant cuts like the classic emerald cut can be produced on modern faceting machines using precisely calculated dimensions. As a number of knowledgeable posters have pointed out, both faceting machines and traditional cutting methods can both produce excellent results.

 

[LadyBlue]

Date: 10/17/2009 9:30:14 PM
Author: morecarats

Date: 10/17/2009 9:19:15 PM

Author: gaby06

For stones like emeralds, saphires and rubies I love native cuts. For me precision cut in stones like emeralds, saphires and rubies just look cheap. While native cuts seem so fancy

, well that just me taste

Gaby06, please don''t confuse the cutting style (step cut, brilliant cut, etc.) with the cutting method. Simple elegant cuts like the classic emerald cut can be produced on modern faceting machines using precisely calculated dimensions. As a number of knowledgeable posters have pointed out, both faceting machines and traditional cutting methods can both produce excellent results.

Thanks more carats

, you are right. What I was meaning is that step cuts look so much better than brilliant cuts for color stones like emeralds, ruby and saphires.

I hope this time I got it right

For diamonds, I love brilliant cuts, as you can see in my avatar

 

[arjunajane]

Thanks Gene for bringing some clarity to this thread,
your comparison was very informative.

 

[T L]

Gene does your software take into account the natural extinction in a stone? Not all material is identical, as we very well know, and in order to cut it to provide maximum light return and color intensity, the stone''s table may have to be cut along a particular axis, or larger facets may bring out more of the sparkle from a more extinct type of material. To me, that''s where the lapidary is more of the artist, and where the computer cannot always help. I could be wrong, unless you have the software that can perform that type of analysis as well?

 

[AustenNut]

Gene,

Thanks for posting all of this. Very informative!

 

[Sagebrush]

Gene,

Wonderful example. Now I know why I like and buy (the sincerest form of flattery) your gems.

I agree as Voltaire said, "If your would discourse with me, define your terms." The term "native cut" is not really a cut, it is an excuse given by the dealer for his poorly cut stones. The reasons you enumerate, excepting maybe 5, explain poor cutting.

I question one deduction; that smaller means lighter. It is not the size but rather the length of the light path that determines the saturation and tone of the hue. True, all other factors being equal (proportions, angles, etc), smaller will indeed result in less color.

Weight retention is more than just an selling strategy, it is a religious/cultural bias. From most ancient times in India, the strength of the occult properties attributed to gemstones were enhanced by size and weight. This is why the Tavernier Blue diamond weighed 116 carats when it was originally sold to Louis XIV. The Sun King recut it to the 68 carat French Blue, vastly improving its almost non-existence brilliance and scintillation. The version we know today, The Hope Diamond, was also a recut, but in this case carefully crafted to darken the stone and increase the light leakage to disguise the gem.

I have one question about tilt angle. Why is it that many gems cut to perfect angles, wink out, while bulbous gems show brilliance at a greater angle from the perpendicular?

 

[Gailey]

Gene, Do you have a picture of the stone after it had been re-cut? Beats me why there was an argument about this in the first place. However, I am glad there was because I have learned so much. Thank you for posting all of this wonderful information.

 

[Michael_E]

Date: 10/18/2009 12:16:14 AM
Author: tourmaline_lover
Gene does your software take into account the natural extinction in a stone? Not all material is identical, as we very well know, and in order to cut it to provide maximum light return and color intensity, the stone''s table may have to be cut along a particular axis, or larger facets may bring out more of the sparkle from a more extinct type of material. To me, that''s where the lapidary is more of the artist, and where the computer cannot always help. I could be wrong, unless you have the software that can perform that type of analysis as well?

Extinction can be caused by only three things which are:

1. A closed axis such as in tourmaline. If light gets directed along that axis, it''s a goner and there''s nothing you can do about it except try to keep it going in the right direction. This is really the only "natural" extinction.
2. A deeply colored stone which is cut in a manner that causes so many bounces within the stone that the light is sucked up by the deep color of the stone.
3. Some directions in all cuts will bounce light off in a direction which keeps it from returning to your eyes. This can be "leakage" out the pavilion or a light path which goes out the crown at a very low angle.

Another BIG hitter here is head shadow which is the light which is blocked by your head while you''re viewing the stone. This looks like extinction, but isn''t, it''s just that there''s not enough light coming from that direction and so the stone looks dark in some areas. In Gene''s example, there''s no way to distinguish between head shadow and windowing by the program, (experience and knowing the angles can tell you this).

The other big hitters are inclusions which can scatter light inside the stone and fluorescence which can cause the stone to give off visible light in all directions. Rubies and sapphires which have micro inclusions or strong fluorescence can be cut nearly anyway and still look very nice since much of light coming from the stone is covering up any extinction or head shadow.

As far as I know there is no software which can model different light transmission rates on different axes of a stone. Some types of software can allow you to model "attenuation" or the amount that light is absorbed on every axis and this is handy for modeling deeply colored stones and novel cutting methods or carvings. The downside is that some of this software is pretty spendy and requires a lot of computer time to get accurate images. Most cutters either can''t afford the software and time to learn it or can''t afford the time to model most of the stones they''re cutting and so just design their cuts based on experience.

 

[chrono]

I have one question about tilt angle. Why is it that many gems cut to perfect angles, wink out, while bulbous gems show brilliance at a greater angle from the perpendicular?

I wonder about the above question posed by Richard as well.

 

[PrecisionGem]

Well, that''s a hard question to answer with out seeing the stones in question. First, you need to compare the same material. If you are looking at a precision cut citrine, and comparing that to a sapphire, the lower refractive index of the quartz will make it window much sooner. Then was the precision cut stone actually cut to the optimum angle in the first place? A deep cut stone, not fat belly like the example above can perform well on a tilt too. Any comparisons need to made with similar materials.

 

[Michael_E]

I''ve been looking at this and the "tilt window" thing very closely over the last couple of days and Gene is right about reducing tilt windows via higher crown and smaller tables. It turns out that you can reduce this further by cutting the crown and pavilion at just the right ratios in the Portuguese cutting style, (I''ve only been looking at round cuts, but others should be similar). Basically a well done "native" cut is similar to the Portuguese style, except for being step cuts and not alternating index cuts. Anyway it turns out that the steep pavilion facets combined with mutiple tiers of facets reduces tilt windowing a great deal, BUT at the cost of having perimeter of the stone being dark. Typically you don''t notice that dark perimeter so much since you''re usually moving the stone around and when you tilt it the perimeter lights up dramatically while the tilt window is rather small and not as noticeable in comparison.

I do think that it''s rather rare to find the right combination of crown height, pavilion depth and number of tiers in a native cut stone, just because it takes a lot of time to get all these things just right and that''s a luxury that most third world cutter don''t have, (not to mention equipment doesn''t lend itself to repeated cutting accuracy). On the other hand, I do think that they can do a pretty good job if they have a day or two to mess around with a high end stone...their employer knowing that a decent cut AND good weight return will maximize their profit. I think that this discussion has some disagreements mostly because many people are talking about two different things. Gene''s talking about slam-bam cutting and those of you who''ve seen nice native cuts are talking about stones which were probably higher end and had more time lavished on them, (or the cutter got a nicely shaped piece of rough and just got lucky in being able to shape it well).