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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 12:15 am 
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TheL wrote:
And on a similar note to the improvement in gemology towards describing colour objectively/accurately: I believe the colour of gemstones should be judge through a window of it infront of neutral white paper under a specific illuminant. Judging colour that has been reflected several times within the stone has too many variables like dispersion, accumulation of saturation depending on bounces, depth of stone, etc. Using just the absorption colour would be more objective.
my humble 1 cent.


My problem with this is that many gems look different under different lights. The topaz on my finger is blue purple under some lights (like a cloudy day) and intense pink under others.


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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 1:10 am 
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My issue with it is that the color of the stone is affected by the cutting. Eliminating it as a variable probably makes the metric less accurate to what you really want to measure.

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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 1:19 am 
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Fair enough, BUT the color of the gem is the color of the gem. If cutting results in the appearance of more saturation (or less), the stone is what it is. No?


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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 1:52 am 
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Barbra Voltaire, FGG wrote:
Fair enough, BUT the color of the gem is the color of the gem. If cutting results in the appearance of more saturation (or less), the stone is what it is. No?

The goal of the measurement is ultimately to quantify the ground reality (how the gem looks). Ignoring or eliminating variables like that means we're just measuring a proxy for the appearance which may or may not correlate. A perhaps unfair analogy being measuring surface reflection as a proxy for refractive index.
I dunno, it seems like this type of metric can only really be useful in a particular context where most variables are controlled. Trying to do it universally seems like a giant headache that would either have to include a ton of data which requires extensive interpretation or be simplified to the extent that it gives a false sense of precision.

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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 1:04 pm 
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Gemology :smt017
Science or Art?
That's one reason I think the Pantone scheme should be used for gems. It is accessible to all.
Continuing the analogy, the color of fiber, paint, most anything can be duplicated currently and correctly with the tools we have available.
Check this out
https://www.printkick.com/tools/image-colour-match



In the case of color shift or color change stones, light temperatures for viewing can be noted.

This has been done for ages in the fashion industry, as well as for duplicating colors needed in antique restoration.


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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 1:12 pm 
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It's a lot easier conceptually with opaque, uniform colors. We can certainly make a pretty good general metric I think, but I think there will always be hard limits on just how thorough we can be within the context of practical use in the gem trade.

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 Post subject: Re: How would you define this sapphire’s colour?
PostPosted: Sun Feb 13, 2022 2:07 pm 
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Just thought, does anyone think the gizmo color readers would work accurately on gem types?

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