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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Sun Aug 29, 2021 11:29 pm 
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I do believe that being in a gem and mineral club and handling a lot of mineral/gems is of some value. However, when the RRUFF guys analyzed thousands of minerals from museums and important collections using XRD, SEM, etc., they found that roughly 1/4 of them were misidentified.

Yes, the experts get it wrong if they are just looking at a stone.

Cut gems are much harder than those where you can identify the crystal shape, so that is why we ask for information, and more information when looking at a gem stone. Since alexandrite is so valuable, there have been a LOT of "fakes", including vanadium doped sapphire (which is quite common, even in gold), synthetic alexandrite, and various glasses. I have even seen a color changing (blue) garnet misidentified as alexandrite. But since it is rare in its own right, I think that was just a mistake.
There is a reason for people to be skeptical, and wondering HOW an id was made.


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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Thu Sep 09, 2021 5:42 pm 
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Is photoshop really that frowned upon? I see it as a must. Specially to calibrate the colours on the photo to match what the eye really sees. No current camera/sensor is able to accurately represent most gems spectra correctly. Specially true for Colour changers.


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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Thu Sep 09, 2021 7:37 pm 
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TheL wrote:
Is photoshop really that frowned upon? I see it as a must. Specially to calibrate the colours on the photo to match what the eye really sees. No current camera/sensor is able to accurately represent most gems spectra correctly. Specially true for Colour changers.



Actually, yes it is possible for a camera to accurately capture stone color. This is camera and workflow dependent. It does take a sophisticated approach to set the proper white balance either in camera or in post processing. It also takes a calibrated monitor to display the colors accurately.

Here is some excellent work done on this by PDN, Image Engineering, and X-Rite/Pantone (the Worlds leading authority on color).

https://pdnonline.com/gear/cameras/the- ... on-ranked/

I do have a camera/computer/monitor/printer setup that is entirely color calibrated to each other. However, most times I end up taking gem images with my cell phone which is definitely not.


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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Thu Sep 09, 2021 10:41 pm 
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Me too. I take jewelry photos with my iPhone. I always open them in PhotoShop and correct anything I deem needs a correction for appraisals. Not to deceive of course, but to accurately depict colors, tones and saturation.


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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Thu Sep 09, 2021 11:56 pm 
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Another very very deep subject. Yes agree that it is completely possible to setup a very accurate photo studio for gem and mineral photography, where very little is needed other than balancing the light in your environment. Then that will depend on the lighting used. Light boxes can sometimes have bulbs that are not balanced as well. You made my brown eyes blue is never a good thing if your being honest in your representation.

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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Fri Sep 10, 2021 6:14 am 
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I don't entirely disagree with you 1bwana1. I know exactly what you mean about correct, balanced equipment from acquisition to display to printing. I work in the digital visual field of cinema, and know exactly what you are talking about. BUT cameras are not an eye->brain. And they are nowhere close in capturing the idiosyncrasies of some minerals' spectra. From the very onset, the human Eye trichromatic sensitivity curves are different from a camera sensor's sensitivity for practical and limitation reasons(not even considering the brain vs camera software). In most cases this is not an issue, but when it comes to Color change stones with strange absorption spectra or any stone with other forms of luminescence like daylight fluorescence, camera sensors fall way short, even for the the 200 thousand dollar sensors from film cameras like the Alexa ARRI.
Its a subject I am deeply interested into, and one I deal with every day. I am no expert mind you, but am surrounded by experts every day.


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 Post subject: Re: Most likely ID for gem that changes colour.
PostPosted: Fri Sep 10, 2021 1:29 pm 
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As soon as an image leaves your possession an onto some other public device, all bets are in favor of, it is most likely to be moot. If we all used the same monitors calibrated with the same color calibrations, and we all have the same human optical capabilities, my bet is still on it is moot. You do the best you can to represent the gem with accurate descriptions as per the trade, and an image that is not over post processed. Many if not all of the most used gem photographers, use post processing in their images. It is frowned upon when it is evident someone doesn't know what they are doing or trying to be deceptive. If we just pass around images to other photographers for criticism and YouTube entertainment then that I guess :-k is a deeper subject entirely.

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