Color change garnet

[zeolite]

Color change garnet, 1.27 cts, East Africa

This garnet has a very strong pink-red in incandescent light, and then goes nearly colorless under fluorescent light. The gem is actually a very pale green, which does not show clearly in this picture.

 

[Richard M.]

zeolite,

Nice stones. I just received a nice rough parcel of the Wandanyi, Kenya material shown in your image #2.

Fluorescent light covers a huge color temperature range. My color change garnets often show an entirely different color under fluorescent than in natural sunlight, even so-called "daylight" fluorescents in the 5,000-6,000 K range. I''ve always considered incandescent light around 300 K and sunlight between 10 a.m. and 4 p.m. the only real way to illustrate color change in gems.

I did my GIA colored stone courses when CC garnets were still rare and not well studied. Does GIA currently make any color temperature recommendations for viewing/grading/photographing CC gems? I haven''t been able to find out.

Richard M.

 

[GemRite]

Hey Zeolite, Nice stone by the way. You can try correcting the color by using the whitebalance and a sheet of white paper. I know noticed on your photos the white back grounds were showing the color of the light. Reddish tone for incadescent and the light blue for natural or flourescent. This will help showing the color of the pale green stone better. I appreciate you charing the stones you have. I would post my color change garnets expect i would be breaking posting policy. My color change stones go from pinkish purple or pink to a yellow or orange color. I think the color change i have are unusual they come from the Tunduru region of Tanzania, but the Madagascar material is nice as well. Red to a nice blue. I also have a friend who has a piece of Madagascar CC garnet rough that is colorless (white) in one light and a red color in the other. The only one I have ever heard of or seen. Super rare. We all know of the red to greens and the red to blues-purples. But the other color change we don''t see much of is nice as well. Pink to yellow or pinkish purple to orange and even the white to red. Nice that we have diversity

I would like to know your thoughts on other color changes as well.

 

[zeolite]

Date: 9/4/2008 12:57:29 AM
Author: Richard M.
zeolite,

Nice stones. I just received a nice rough parcel of the Wandanyi, Kenya material shown in your image #2.

Fluorescent light covers a huge color temperature range. My color change garnets often show an entirely different color under fluorescent than in natural sunlight, even so-called ''daylight'' fluorescents in the 5,000-6,000 K range. I''ve always considered incandescent light around 300 K and sunlight between 10 a.m. and 4 p.m. the only real way to illustrate color change in gems.

I did my GIA colored stone courses when CC garnets were still rare and not well studied. Does GIA currently make any color temperature recommendations for viewing/grading/photographing CC gems? I haven''t been able to find out.

Richard M.

The pictures posted yesterday was my first successful attempt at merging both photographs into one .jpg picture. I have another probably full spectrum fluorescent bulb to try for the "daylight" picture. Yes, different fluorescent bulbs will give different results.

Also, the incandescent bulbs I am using, are GE Reveal bulbs, which are full spectrum bulbs. They appear to be an ordinary incandescent bulb, coated with a blue dye. What this does, is reduce the red part of the spectrum, while passing much more blue than normal. What this should do, is make the incandescent picture MUCH closer in color to the fluorescent picture, strongly reducing the color change effect. I have much experimenting to do, on these 6 gems shown here. The results could be quite different.

I don''t know what GIA''s recommendation is presently. I do have a chemical analysis of the spinel. and possibly the sapphire, done by Dr. Shigley of GIA, about 1990. Without looking up the report, I seem to remember that traces of vanadium contributed to the color change effect.

 

[Pandora II]

Very nice stones Zeolite!

I am extremely envious of your collection.

I have just the one colour change and it''s a small and not particularly fine stone. But, the change is very good. Here are a couple of photos:

This is in daylight - it''s a touch grayer than it looks in the photo but still very blueish purple.

 

[Pandora II]

And in incandescent light:

It shows a bit of a purple flash as well. I''ve been taking some photos but they''re not great sadly. I''ll post one when I catch it right. These photos are the vendor''s.

 

[zeolite]

Date: 9/4/2008 6:04:37 PM
Author: Pandora II
And in incandescent light:

It shows a bit of a purple flash as well. I''ve been taking some photos but they''re not great sadly. I''ll post one when I catch it right. These photos are the vendor''s.

Wow, that''s a strong change. You should be proud to have such a fine, rare gem!

 

[Pandora II]

Thank you.

Sadly it has a whopping big crack that seriously compromises the stone. Fortunately it's only visible from the back due to it's position. It's just about visible in the top left hand corner of the second picture.

I paid very little for it, so I wasn't bothered - the colour was what I was after.

It has a safe and happy home in it's box!

 

[zeolite]

Date: 9/4/2008 1:55:54 AM
Author: GemRite
Hey Zeolite, Nice stone by the way. You can try correcting the color by using the whitebalance and a sheet of white paper. I know noticed on your photos the white back grounds were showing the color of the light. Reddish tone for incadescent and the light blue for natural or flourescent. This will help showing the color of the pale green stone better. I appreciate you charing the stones you have. I would post my color change garnets expect i would be breaking posting policy. My color change stones go from pinkish purple or pink to a yellow or orange color. I think the color change i have are unusual they come from the Tunduru region of Tanzania, but the Madagascar material is nice as well. Red to a nice blue. I also have a friend who has a piece of Madagascar CC garnet rough that is colorless (white) in one light and a red color in the other. The only one I have ever heard of or seen. Super rare. We all know of the red to greens and the red to blues-purples. But the other color change we don''t see much of is nice as well. Pink to yellow or pinkish purple to orange and even the white to red. Nice that we have diversity

I would like to know your thoughts on other color changes as well.

A normal way to set the white balance in a photo is to set whites in the picture to pure white.

But I was trying to show the gem''s actual color, and did so, in Photoshop. I completely ignored the background color, which as you noticed, is faintly blue white in fluorescent light, and a much stronger pink in incandescent light. If I set the background in each photo to pure white, the gem color would be quite wrong. With my knowledge in Photoshop, I could set the gem to the correct color, mask it out, and then set the background to pure white. But I think that is misleading and unethical.

I''m not sure if the average reader here is aware of how easy it is to fake a color, to make the color change seem stronger than it really is. I saw an auction in e*ay, where all of the gems had hyper-saturated color. I''ve seen enough gems in 25 years to know that color is not real. Yet the intense color probably helps them sell many more gems, until the buyer finds out that the auction picture is not accurate.

There was a reference in the alexandrite e-ring thread, that led to a company specializing in alexandrite. Their photos showed nearly the same slightly blue white background that I got. Their incandescent picture was more orange (mine was more pink) which showed that they were using a different incandescent bulb than my Reveal bulbs. My point is, I thought they were cheating, trying to make the fluorescent color more blue, and the incandescent color more red. After shooting my pictures yesterday, I just realized that they were doing exactly as I was, trying to get the gem color correct under each lighting, and just letting the background color fall to whatever color that might be.

I''d love to see a picture of your purplish pink to orange, and white to red. I haven''t seen those changes. I have about 8 other color change gems that I have not pictured, because their change is not so strong.

 

[Richard M.]

Date: 9/4/2008 12:16:04 PM
Author: zeolite

I don''t know what GIA''s recommendation is presently. I do have a chemical analysis of the spinel. and possibly the sapphire, done by Dr. Shigley of GIA, about 1990. Without looking up the report, I seem to remember that traces of vanadium contributed to the color change effect.

Vanadium seems to be present in most color-change gems other than alexandrite. It''s occurrence is widespread in Africa which probably accounts for the many color-change garnet and corundum occurrences there. It is even an isomorphous replacement for chromium in Zambian and some other African emeralds.

As for my lighting question, it seems to me that images of CC gems can be rather misleading without specifics about the type of lighting used, combined with an understanding on the part of the consumer as to why it can make a big difference. If you go to gem shows you''ll see vendor after vendor demonstrating color change with a "daylight" Ott lamp. Yet my own tests have shown the actual daylight color of stones is very different more often than not.

These days, when a lot of gem trading is done with images on the internet, it seems to me that GIA or maybe the Lab Harmonization group should set some international lighting standards for judging color change, not just simply "incandescent" and "fluorescent." That way a buyer in Scranton, say, using the same lighting as a seller in another location, should expect the gem to look the same.

I''ve refrained from trying to sell my CC stones because there are big misunderstandings about them on the part of consumers. I just trashed a large number of images that took me long hours to make because they showed different background colors just like yours. Thanks for your contribution to better understanding about that. I felt certain potential clients would suspect some photographic trickery if I used similar images.

Richard M.

 

[Pandora II]

Date: 9/5/2008 11:44:10 AM
Author: Richard M.

Date: 9/4/2008 12:16:04 PM
Author: zeolite

I don''t know what GIA''s recommendation is presently. I do have a chemical analysis of the spinel. and possibly the sapphire, done by Dr. Shigley of GIA, about 1990. Without looking up the report, I seem to remember that traces of vanadium contributed to the color change effect.

Vanadium seems to be present in most color-change gems other than alexandrite. It''s occurrence is widespread in Africa which probably accounts for the many color-change garnet and corundum occurrences there. It is even an isomorphous replacement for chromium in Zambian and some other African emeralds.

As for my lighting question, it seems to me that images of CC gems can be rather misleading without specifics about the type of lighting used, combined with an understanding on the part of the consumer as to why it can make a big difference. If you go to gem shows you''ll see vendor after vendor demonstrating color change with a ''daylight'' Ott lamp. Yet my own tests have shown the actual daylight color of stones is very different more often than not.

These days, when a lot of gem trading is done with images on the internet, it seems to me that GIA or maybe the Lab Harmonization group should set some international lighting standards for judging color change, not just simply ''incandescent'' and ''fluorescent.'' That way a buyer in Scranton, say, using the same lighting as a seller in another location, should expect the gem to look the same.

I''ve refrained from trying to sell my CC stones because there are big misunderstandings about them on the part of consumers. I just trashed a large number of images that took me long hours to make because they showed different background colors just like yours. Thanks for your contribution to better understanding about that. I felt certain potential clients would suspect some photographic trickery if I used similar images.

Richard M.

I tried mine with one of them, but the only way it shows the colour in the photo is slightly overcast daylight. Any sun starts to bring out the pink colour.

My own personal take is that I would like the colour of the photo to be as close as possible to the actual stone. One of the differences with buying gems from a vendor''s website as opposed to somewhere like ebay is that you are likely to get a feel for accurate representation - especially with a place like PS where people will post photos and opinions on both the stones and the place they bought them.

On ebay, unless I knew the vendor from a stand alone website (I know some people sell on both), I almost certainly would never buy anything unless they had great feedback from people who it was obvious knew what they were talking about. (I check a vendor''s buyers out to see what they are buying/spending on gemstones).

Otherwise, an explainatory paragraph in the description goes a long way to allay any fears.

 

[zeolite]

Date: 9/5/2008 11:44:10 AM
Author: Richard M.

Date: 9/4/2008 12:16:04 PM
Author: zeolite

I don''t know what GIA''s recommendation is presently. I do have a chemical analysis of the spinel. and possibly the sapphire, done by Dr. Shigley of GIA, about 1990. Without looking up the report, I seem to remember that traces of vanadium contributed to the color change effect.

Vanadium seems to be present in most color-change gems other than alexandrite. It''s occurrence is widespread in Africa which probably accounts for the many color-change garnet and corundum occurrences there. It is even an isomorphous replacement for chromium in Zambian and some other African emeralds.

As for my lighting question, it seems to me that images of CC gems can be rather misleading without specifics about the type of lighting used, combined with an understanding on the part of the consumer as to why it can make a big difference. If you go to gem shows you''ll see vendor after vendor demonstrating color change with a ''daylight'' Ott lamp. Yet my own tests have shown the actual daylight color of stones is very different more often than not.

These days, when a lot of gem trading is done with images on the internet, it seems to me that GIA or maybe the Lab Harmonization group should set some international lighting standards for judging color change, not just simply ''incandescent'' and ''fluorescent.'' That way a buyer in Scranton, say, using the same lighting as a seller in another location, should expect the gem to look the same.

I''ve refrained from trying to sell my CC stones because there are big misunderstandings about them on the part of consumers. I just trashed a large number of images that took me long hours to make because they showed different background colors just like yours. Thanks for your contribution to better understanding about that. I felt certain potential clients would suspect some photographic trickery if I used similar images.

Richard M.

I''ve given a lot of thought about your comments of fluorescent vs sunlight on color change (c/c) gems.

I looked my daylight fluorescent that I used in my c/c posts. It is a GE F14T12-D daylight bulb. It has a CRI (color rendering index) of 75 and color temperature of 6500K; actually poor at imitating daylight, in spite of the daylight name. I have two F15T8/Excella bulbs that I''m going to try; I ordered fixtures today. This bulb has a CRI of 91 and a color temperature of 5765K. Daylight, according to this website, has CRI of 100, color temperature of 5500K. In addition, some OTT bulbs are listed at a CRI of 94, and one company, fullspectrum solutions, claims a CRI of 96! I looked at the spectrum of the F15T8/excella bulbs, and they only differ from sunlight in the red region; all other colors match well with sunlight.

I''ve now spent about $150 on lighting in the last two weeks for gem photography (diffusers, wooden fixtures, two new ballasts and fixtures to hold the F15T8/excella bulbs). Maybe I should just buy gems instead!

I think a flourescent with a CRI of 91 or better should be a fair stand-in for daylight, with the exception of red gems, where no phosphor can reproduce that color correctly. If a CRI of 96 isn''t good enough, I don''t know what to propose. Perhaps we are splitting hairs.

To further confuse the issue, what is sunlight? Direct full sun at noon, with a white acrylic diffuser held above, to smooth out the harsh light? Full shade at noon on a sunny day? Or as Pandora suggests, and overcast day? All three sunlight conditions will produce different results.

I think the best answer here is full sun with diffuser. The colors seem quite rich this way, whereas the undiffused shade picture looks washed out, bluish, and dull.

Below is my c/c sapphire, full sun at noon, in the shade, no diffuser on the left. On the right, full sun at noon with diffuser. I tuned the colors in Photoshop to match what I see. Again, notice the color tint in the background. I think it is an un-avoidable result of matching the gem color correctly. As I said, I can fix the background color to white, but I think that is cheating, and misleading. Next post below, the c/c diaspore.

 

[zeolite]

Below is my c/c diaspore, full sun at noon, in the shade, no diffuser on the left. On the right, full sun at noon with diffuser. I tuned the colors in Photoshop to match what I see. The yellowish sunlight picture is correct. The shade picture shows a bluish-green, whereas I actually see a slightly yellowish-green, Even with Photoshop, there are some pastel colors that I can’t correctly match.

 

[zeolite]

While the diaspore picture seems to be a strong change, it is only because yellow is the narrowest color in the visible spectrum. You can go from yellow-green at 565 nm to golden at 580 nm, a 15 nm spread.

In red, a broad color, you can go from 650 nm to 700nm, a 50 nm spread, and still be the same red.

 

[Richard M.]

zeolite,

Your reports above are interesting and helpful. My initial comments really had nothing to do with your images per se. I was just wondering why GIA can set standards on so many other aspects of gemology but apparently hasn''t come up with a lighting standard for both colored and color-change gems. My own experience trading in gems and photographing them has highlighted these questions.

One lighting authority, quoted in a 1999 Colored Stone article by Marlene A. Prost, said the following:

"Both CRI and Kelvin are false standards, used to trick the trade and the consumer...I can get three fluorescent lights with the same Kelvin rating and to the eye each light looks different. Kelvin isn''t without meaning. It''s just too broad a range as a standard."

He also found fault with CRI, calling it "misleading." If a lamp is rated over 5000K, it is being based on daylight; but if the Kelvin is below 5000K, the color index is based on incandescent light.

"How can we listen to a lamp [sales] person when...one is saying his product is great because it compares to daylight, while the other says theirs is good because it compares to [incandescent]?"

So to respond to your CRI example I quote the same expert:

"Yes, it''s easy to get a 98 CRI when you''re comparing [the light] to an incandescent. But if you push the temperature to 5000K the CRI will drop to 60 or 70." I have no idea what your lamp''s CRI was comparing to, by the way.

The experts I''ve studied seem to agree the only accurate and measurable way of comparing light sources is the spectral output of their color. So far as I know, no current gemological authority has addressed that matter in a practical way that helps in transacting colored gem business.

Richard M.

 

[zeolite]

"Yes, it''s easy to get a 98 CRI when you''re comparing [the light] to an incandescent. But if you push the temperature to 5000K the CRI will drop to 60 or 70." I have no idea what your lamp''s CRI was comparing to, by the way.

Below is the semi-spectrum of the Excella lamps I''m going to try, the Kelvin temperture is above 5000K and the CRI is based on daylight, not incandescent. Graph 1 shows daylight, graph 2 shows Excella, and graph 3 shows the daylight fluorescent I used in my c/c pictures.

The experts I''ve studied seem to agree the only accurate and measurable way of comparing light sources is the spectral output of their color. So far as I know, no current gemological authority has addressed that matter in a practical way that helps in transacting colored gem business.

I agree that is the only accurate way. I have run 4 different spectro-photometers in my physics jobs the last 20 years, including a $37,000 Photo Research PR 705. I could probably get permission to run it now on these Excella lamps. I am the only one at that company that knows how to run that research instrument.

You didn''t comment on the correct version of daylight to use in c/c pictures. Your ideas?

 

[Richard M.]

zeolite,

To quote you about actual daylight: "To further confuse the issue, what is sunlight? Direct full sun at noon, with a white acrylic diffuser held above, to smooth out the harsh light? Full shade at noon on a sunny day? Or as Pandora suggests, an overcast day? All three sunlight conditions will produce different results."

When I first responded to this thread I merely questioned the fact there is no worldwide standard. Frankly, it makes little difference to me which of the three possibilities mentioned above is duplicated. What counts with me is if a person 5,000 miles away can obtain the same visual results under the same conditions as the person doing the photography. It''s important that light sources as close as possible to real daylight and some arbitrary incandescent choice (candle light, 100 watt clear bulb, Reveal bulb?) be specified. It''s a mystery to me why the gem labs, which would seem to be the logical organizations to create such trading standards, have seemingly ignored this rather obvious problem. No matter what artificial lighting standards are chosen, none will be able to duplicate natural conditions exactly, that''s a given. But I think we can do much better than at present. But maybe I''m overlooking some important factors.

From your spectroscopic presentation the Excella appears to be a very good daylight choice. I''m not an expert in that field so I don''t know what else might be available. I do know some people who are working on the question and I''ll send them an inquiry to see if I can get up to date ideas on their work.

Richard M.