Color/hue of spinels

[Starstruck8]

I think Chroma and saturation are loosely the same thing.

I sort of agree, but I would put it a bit differently. ‘Saturation’ is used loosely to describe at least three different concepts related to strength of colour. See the illustration below.


In (1), saturation is based on the ratio of chroma to the maximum possible chroma for the given hue. This seems to be what gemstone grading systems are doing (as far as I can tell, which isn’t very far…). In (2), saturation is based on the ratio of the chroma to the maximum possible chroma for the given hue at the same tone. This is used, for example, in the Photoshop Elements colour picker. It also allows you to say, for example, that a particular pink stone is highly saturated, even if its chroma may be lower than that of a saturated red stone – it’s highly saturated, so to speak, for that tone of pink. The CIE definition is illustrated in (3). This compares the ratio of brightness to chroma to the maximum possible ratio for the given hue.

Finally, look in person at various hues of high quality gems at an institution like the Smithsonian or a high end gem show, to see for yourself what truly vivid color is about.

I think the best education in color is to go look, in person, at top gems. It’s not the easiest thing to do, but over the course of collecting many years, I feel that no one can teach color through a photo or gemset or software as much as seeing the real thing in person. Once you see truly vivid gems, it gives you a whole new perspective.

+100. There is no substitute for seeing top stones with your own eyes. That said, it's not so easy for those of us who live in out-of-the-way parts of world.

 

[fredflintstone]

I think Chroma and saturation are loosely the same thing. I think the Munsell system is just more complex. The GiA gemset is a simplistic device that helps give one an idea of what color, saturation and tone the gem is. I’ve seen it subjectively used however, and what is one person’s vivid is not necessarily another’s opinion. Some gem labs have higher standards, and some well, they just want to sell lab reports.

In the end, I think the best determination of a colored gem is to take it to a reputable gem lab, and get a scientific/unbiased report determining its color. Avoid metaphors to describe gem color (ie “pigeon blood”). Finally, look in person at various hues of high quality gems at an institution like the Smithsonian or a high end gem show, to see for yourself what truly vivid color is about.

The Gemset was an unbiased comprehensive way to grade color in gemstones from a reputable lab, and the GIA Gemset in my opinion still is unmatched. As is the AGL's system being unbiased.

But the rub here is each individual may see (interpret) color differently. So, nothing is perfect, especially a unified perception of color from individuals and there is no way to make it so, only come close.

 

[LilAlex]

I can't add much except to point out (if it is not above, already) that some of this is an artifact of English. It has been said here that many languages have a unique color name for some lighter shades -- like of blue or purple. In English, light blue is still "blue" and light green is still "green" and light orange is still "orange." But light red is pink. Maybe because there is so much (biological) pink in nature or because it is so appealing? Or freighted with gender significance? Or from such pervasive marketing...?

(And I know that light blue, for example, has many other names from cornflower to periwinkle but as a hue, we English-speakers would agree that they are all various flavors of "blue.")

 

[Autumn in New England]

The Gemset was an unbiased comprehensive way to grade color in gemstones from a reputable lab, and the GIA Gemset in my opinion still is unmatched. As is the AGL's system being unbiased.

But the rub here is each individual may see (interpret) color differently. So, nothing is perfect, especially a unified perception of color from individuals and there is no way to make it so, only come close.

I fully agree with this ^. You guys are so thorough. When I get to a thread late or miss a bunch, there's nothing left to say!

 

[JewelledEscalators]

I have a Lotus certified red/pink spinel that says vivid to intense. Haven't paid much attention to it as I thought it was just a subjective classification by one lab...