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CIE color comparison between cuprian and non cuprian tourma.
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Author:  bruce_tourm [ Tue Aug 29, 2017 7:53 pm ]
Post subject:  CIE color comparison between cuprian and non cuprian tourma.

It has been a struggle between an upgrade and a problem with a factory adjustment, but my spectrometer is up an running well. This brief post is just to give you an idea of what I am working on. I would be happy to try and answer any questions you might about this preliminary data.

The tourmaline I am testing is five sets of gemstones, that I have matched by eye, to have similar colors. One of each pair is cuprian by my spectrometers data and the other is non cuprian. I believe all the cuprian tourmaline came from Mozambique while the non cuprian could have come from anywhere, but I suspect that most of it is African. The non cuprian cyan is from Afghanistan.

The numbers I have assigned to the tourmaline can be used to look up pictures of them on my site BRUCEFRYTOURMALINE.com While the pictures and description are interesting, the main point I am trying to make with the comparison is that that many, if not most, cuprian colors are NOT unique to cuprian tourmaline.

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I have posted before why I think some cuprian colors have a glow like appearance and others are brighter, so I won't go into it here, but I think that some of the data present here is provocative.

Bruce

Author:  gembug [ Sun Sep 03, 2017 1:48 am ]
Post subject:  Re: CIE color comparison between cuprian and non cuprian tou

Hey Bruce, give me a couple of days and I'll try to link to the pics of your stones and find a more visual way to display your spectrometer data. Right now it's very hard to understand what the data is saying.

-Allan

Author:  Barbra Voltaire, FGG [ Tue Sep 05, 2017 3:52 pm ]
Post subject:  Re: CIE color comparison between cuprian and non cuprian tou

Hi Allan.
I reformatted Bruce's post.

Author:  gembug [ Fri Sep 08, 2017 2:17 am ]
Post subject:  Re: CIE color comparison between cuprian and non cuprian tou

Thanks Barbra.

I'm still puzzling over how best to show this. Below is my attempt to explain in simple terms what the numbers are showing.

The numbers for each pair of stones are showing the difference between the stone in question and an unknown reference. But that unknown reference is ok, because it is the same for each comparison which means the numbers are showing how much different each stone is from the reference.

Comparing two stones to each other, for example the Purple:

715 - non-cuprian Hue=-19.1; Chroma=17.1; Lightness=41.7
572 - cuprian; Hue=-18.0; Chroma=42.7; Lightness=40.6

The data is showing that Bruce's eye is pretty good for matching the same hues and lightness (they're only off by a slight amount). But the significant difference between them is that the Cuprian stone has much greater Chroma values.

According to Wikipedia, Chroma is "the colorfulness relative to the brightness of a similarly illuminated white". https://en.wikipedia.org/wiki/HCL_color_space

So what the data is showing is that the intensity of the hue for the cuprian of the two purples is much stronger than the non-cuprian, with the other factors largely being equivalent.

What's interesting is that the Red pair do not show this, but an inverse correlation - that is, the Cuprian stone shows lower Chroma than the non-cuprian. This may be due to the stones not being as well matched a pair in absolute colour terms as noted by the rather large differences between them in Hue and Lightness values.

I'll be posting links to the pics themselves in the coming days so you can see for yourself how they appear, at least to the camera :wink:

If I've made any errors please feel free to correct me. I'm not a colour scientist by any stretch so I've done my best to interpret the results through my rose-tinted glasses :D

-Allan

Author:  Stephen Challener [ Fri Sep 08, 2017 8:50 am ]
Post subject:  Re: CIE color comparison between cuprian and non cuprian tou

So essentially the saturation is higher?

Author:  gembug [ Fri Sep 08, 2017 2:09 pm ]
Post subject:  Re: CIE color comparison between cuprian and non cuprian tou

That would be a simpler interpretation :)

Now what role copper plays in that will be interesting to know. I suspect it has something to do with maintaining the purity of the colour and not having other hues interact/mask it.

Something that mightier minds than mine will have to investigate!

-Allan

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