I think I just learned something...

[Kelli]

Technically speaking I know what saturation is, but I could never figure out how you guys were judging saturation from photos and videos of gems. I think I've now realized that what I was seeing as "contrast" is really a lack of saturation. In my diamonds I always looked at the contrast between the dark and the light; it makes the facet patterns really stand out in some lighting and I viewed it as a good thing. I guess I saw colored gems the same way, thinking the brighter reflections combined with the darker areas of extinction made for interesting contrast and sparkle. I don't know how "sparkle" itself is affected, but I'm now guessing the ones without those darker areas are the highly coveted "glowy" stones? And those are more saturated?

Please correct me if I'm wrong. I'd really like to get a better eye for this stuff. Thanks in advance!

 

[T L]

Technically speaking I know what saturation is, but I could never figure out how you guys were judging saturation from photos and videos of gems. I think I've now realized that what I was seeing as "contrast" is really a lack of saturation. In my diamonds I always looked at the contrast between the dark and the light; it makes the facet patterns really stand out in some lighting and I viewed it as a good thing. I guess I saw colored gems the same way, thinking the brighter reflections combined with the darker areas of extinction made for interesting contrast and sparkle. I don't know how "sparkle" itself is affected, but I'm now guessing the ones without those darker areas are the highly coveted "glowy" stones? And those are more saturated?

Please correct me if I'm wrong. I'd really like to get a better eye for this stuff. Thanks in advance!

Saturation is the strength of the hue (color) of the gem. A stronger saturated warm colored gem will have less brown in it, and a stronger saturated cool colored gem will have less gray in it. Saturation is also tied to tone (the darkness or lightness of a stone). If a stone is too dark or too light in hue, it will also affect saturation. That's why when you see very dark colored stones, it's hard to see the color well unless you're under a very bright light. If a stone is too light in color, that also means it doesn't have enough hue, and looks "washed out." Stones that are more highly saturated are less extinct, yes.

Saturation can also change with cutting. A lapidary can maximize or minimize the saturation of the stone based on how its cut. A stone that is cut too deep, for example, may look more extinct, than one that is cut more shallow. However, one can lose saturation on a nicely saturated stone if they recut it. People here often don't advise on recutting stones with very good color, because it has been witnessed that they can lose saturation.

 

[chrono]

Seeing brilliance contrast or scintillation is a good thing and is expected, which is what you are describing. Without this, any coloured stone will look dull and lifeless. This is a product of cutting and has little bearing on saturation.

I like Palagem's easy explanation.
http://www.palagems.com/quality_4cs.htm

Colour is broken down into 3 sections: hue (purity of colour), saturation (pop or strength of colour) and tone (light or darkness).
Hue = having modifiers will affect pricing in either a negative or positive way. For example, pure red rubies are more valued than an orangish ruby. A touch of blue in tsavorites are more expensive than a straight green.
Saturation = this where one talks about grey and brown modifiers. A strongly saturated stone will pop like crazy with neon colouration. If it isn't well saturated, it will appear either too warm (brown) or too cold (grey).
Tone = There is a range from overly light (washed out) to overly dark (black out)

These 3 do overlap somewhat but for the most part are 3 separate categories. The pictures in the link will help you see the differences in each category and what they mean.

 

[eastjavaman]

Saturation can be compared to rating in Fancy color diamonds GIA grading, whether it is light, intense, and vivid. Of course in colored stones the saturation are stronger than those of the diamonds (most of the time anyway).e.g. Fancy vivid blue diamonds will actually would not make a desirable blue sapphire as the color appear too grayish as compared to top color kashmir blue sapphire.
Faceting will create color difference in areas in the stone that makes it sparkle, but not until that it is unable to reflect light and appear black in which we know as extinction.
In color such as blue, maximum saturation is achieved with the tone at 85%(medium dark); however, as TL mentioned that when stone is too dark, it is difficult to see the vividness of the color. As you move range from this tone, you will lose saturation as the stone becomes too light or too dark, but this also where personal preference kicks in, I personally prefer tone at about 75%-80%.

 

[movie zombie]

and re extinction:

"The colored stone grading course workbook of the Gemological Institute of America (GIA, 1983) defines extinction in similar vague terms:

Extinction is areas of darkness visible when the stone is judged for brilliance. It is caused by blackness in the stone and the proportion angles. Judge extinction as a percentage or as a fraction of the whole stone. View the stone while holding it both horizontally and vertically and assess the extinction in whatever position it is the least.

The American Gem Market System (AGMS) Network Grading Manual (1986) had this to add about extinction:

"Extinction," or "blackout" in gem materials is a phenomenon most apparent in dark tone stones, but which can be present in lighter tone material also. The effect can be reduced in the middle of the stone by "windowing" during cutting. Orientation of rough during cutting can either decrease or increase the effect, but cannot entirely eliminate it unless the stone is cut too shallow or with almost no BRILLIANCE. When grading extinction, the stone is held face up over a plain white background under diffused daylight lighting, and a judgment is made as to how much (what percentage) of the stone reflects back the true color of the gem and does not "black out." The visible surface of the stone represents 100%. When the stone is tilted slightly in any direction, any extinction present will appear to move from facet to facet. The percentage of the stone which is "extinct" usually remains constant, so an estimation can be made as to what percent of the total area is extinctive. Care should be taken not to confuse dark tone with extinction. Extinction is black, with none of the hue of the stone apparent."

 

[Kelli]

Thanks guys, I appreciate the help. It's fun to go through these threads and make guesses as to the quality of stones people post, and then see the opinions of those who are much more knowledgeable. Maybe someday I'll be able to trust my own eyes too. I just don't have the funds or the opportunity to see many great stones in person.