Question on color grading comparison chart

[Lula]

I found this online (while searching for something else) on the Trade Shop website. I do not know how old it is, but what I found interesting is the comparison of the five grading "systems." Can someone tell me more about these comparisons? What I find fascinating is that GIA seems to have individual categories for each color grade, while the other systems show some overlap, e.g., an "8" includes the GIA colors O, P, Q. Yet, AGS gives each stone a GIA letter grade as well as a number grade. Is this why some stones are referred to as a "high H" or a "low H" for example -- there is not perfect overlap between the systems?

ETA: here's the source of the chart http://www.tradeshop.com/master/color.shtml

 

[Stone-cold11]

Color is continuously varying and not in step gradation as given by grades. Thus so you can have high H, low H. (e.g. If the stone is just below the G grade stone's tint, it is a high H, almost as good as a G.) Also, GIA recently started to merge grades for the more tinted stones, giving grades U-V instead of either U or V.

 

[diamondseeker2006]

Not sure that corresponds to current AGS color grading. I just looked at a stone with an AGS cert and it said 1.5 G color.

When I refer to high H, I am referring to the normal range within any color grade. For example, GOG has a colorimeter that grades color. You can see whether a stone scores more toward a high, mid, or low range of a color grade. I actually have a stone that was graded H by GIA but scored a G by the colorimeter which could indicate that it's color was borderline, and a good buy for me!

 

[diamondseeker2006]

That must be an old AGS color scale. Here is the current scale:

http://agslab.com/ags_grading_system_diamond_color_grade.php

Looks like D is 0 colorless, .5-1.49 E-F essentially colorless, 1.5-3.49 G-J near colorless. etc.

 

[yssie]

JFF -

AGS D IF - Colour 0, Clarity 0 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104044686014
AGS D VS1 - Colour 0, Clarity 3 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104044686132
AGS E VVS2 - Colour 0.5, Clarity 2 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104044686033
AGS F VS2 - Colour 1.0, Clarity 4 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104047809042
AGS G VVS1 - Colour 1.5, Clarity 1 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104047809026
AGS H SI1 - Colour 2.0, Clarity 5 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=BLAGS-104047808008
AGS I SI2 - Colour 2.5, Clarity 6 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104047809001
AGS J VS2 - Colour 3.0, Clarity 4 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104048050052
AGS K SI1 - Colour 3.5, Clarity 5 http://www.briangavindiamonds.com/diamond/diamond-detail/?product_id=AGS-104048050014

No 3.8 for a "worse" K or 3.3 for a "good" K or anything like that

GIA N (Colour graded as N) http://www2.gia.edu/reportcheck/index.cfm?fuseaction=home.showReportVerification&reportno=6107497670&weight=0.50
GIA O/P (Colour graded as range O-P) http://www2.gia.edu/reportcheck/index.cfm?fuseaction=home.showReportVerification&reportno=6127332868&weight=0.90
GIA Q/R (Q-R), but there is no P-Q range http://www2.gia.edu/reportcheck/index.cfm?fuseaction=home.showReportVerification&reportno=2121222291&weight=0.91
GIA U/V (light brown notation) http://www2.gia.edu/reportcheck/index.cfm?fuseaction=home.showReportVerification&reportno=1109941383&weight=0.63

 

[Lula]

Thanks, stone, diamondseeker, and yssie, for the responses.

Yes, diamondseeker, it does look like the chart is an old version; the newer versions have a one-to-one correspondence between the AGS numbers and the GIA letters. Thanks for your explanation of the colorimeter. You did get a good deal on your diamond considering the price jump between those color grades.

Stone, I know that human graders can make errors, but I've always assumed that the color grades are fairly narrow, but apparently they are wide enough to allow distinctions between "high" and "low" color variations within the same grade.

yssie, wow, thanks -- jff, indeed. The new reports show how the systems have dovetailed.

I'm still fascinated by the descriptors on the old chart -- e.g., "Fine White"; "Exceptional White." I think the current system is an improvement since it leaves out the easy-to-misunderstand adjectives, but I think the history of the terminology is pretty interesting (no more blue white by law!).

 

[yssie]

I'd be interested in hearing how some of the names and terms came around too - wesselton, apparently named after a mine?


I also wonder if the single-letter to range cutoff is the same for AGS - N is N, O is O/P?


Thanks for starting (another) interesting thread Lula

 

[Stone-cold11]

Stone, I know that human graders can make errors, but I've always assumed that the color grades are fairly narrow, but apparently they are wide enough to allow distinctions between "high" and "low" color variations within the same grade.

The chart you showed has a continuous range of tint, since it is a range for a grade, there will be a high end to a low end for the same grade. From what I read, master stones color are set at the lower limit of the color grade, so a G color graded stone can only have lesser tint than the G master stone.

 

[slg47]

I think I will start referring to my diamond's color as "Top Wesselton"

 

[yssie]

Stone, I know that human graders can make errors, but I've always assumed that the color grades are fairly narrow, but apparently they are wide enough to allow distinctions between "high" and "low" color variations within the same grade.

The chart you showed has a continuous range of tint, since it is a range for a grade, there will be a high end to a low end for the same grade. From what I read, master stones color are set at the lower limit of the color grade, so a G color graded stone can only have lesser tint than the G master stone.

Quick question - SC maybe you know, do GIA/AGS/EGL use the same master stones (of same size and tint?)

 

[diamondseeker2006]

I would think the days of grading color with master stones and the eyes of the gemologist will not be much longer. Totally accurate and consistent color grading technology has to be a reality. Maybe it just needs to be refined or made more financially accessible, but that does not seem to be too hard to imagine in the relatively near future.

 

[Lula]

I'd be interested in hearing how some of the names and terms came around too - wesselton, apparently named after a mine?


I also wonder if the single-letter to range cutoff is the same for AGS - N is N, O is O/P?


Thanks for starting (another) interesting thread Lula

Thanks, yessie, glad my internet surfing is useful to others (makes me feel better about the time I waste on the net!).

 

[Lula]

Stone, I know that human graders can make errors, but I've always assumed that the color grades are fairly narrow, but apparently they are wide enough to allow distinctions between "high" and "low" color variations within the same grade.

The chart you showed has a continuous range of tint, since it is a range for a grade, there will be a high end to a low end for the same grade. From what I read, master stones color are set at the lower limit of the color grade, so a G color graded stone can only have lesser tint than the G master stone.

You mean a higher tint than the master stone (if the master is set at the low end?). Sorry, the higher and lower terminology can be confusing. To me a "D" is a "higher" color grade; but others refer to it as "lower" because in the alphabet D comes before E, F,...

 

[Lula]

I would think the days of grading color with master stones and the eyes of the gemologist will not be much longer. Totally accurate and consistent color grading technology has to be a reality. Maybe it just needs to be refined or made more financially accessible, but that does not seem to be too hard to imagine in the relatively near future.

Yes, I do believe that using color analysis technology instead of human eyeballs would be beneficial. However, I know that there are others that believe that human graders, by virtue of looking at thousands and tens of thousands of stones over a career, are very consistent. On the other hand, I know that factors other than the color of the crystal as it comes out of the mine can influence color:
cut quality
fluorescence
shape (round vs emerald vs marquis, etc.)
variations in human visual abilities
just to name a few.

 

[Stone-cold11]

Stone, I know that human graders can make errors, but I've always assumed that the color grades are fairly narrow, but apparently they are wide enough to allow distinctions between "high" and "low" color variations within the same grade.

The chart you showed has a continuous range of tint, since it is a range for a grade, there will be a high end to a low end for the same grade. From what I read, master stones color are set at the lower limit of the color grade, so a G color graded stone can only have lesser tint than the G master stone.

You mean a higher tint than the master stone (if the master is set at the low end?). Sorry, the higher and lower terminology can be confusing. To me a "D" is a "higher" color grade; but others refer to it as "lower" because in the alphabet D comes before E, F,...

Ya, definition. :p

Lesser tint, higher color grade, with D grade better, higher color grade than E grade.

 

[slg47]

I would think the days of grading color with master stones and the eyes of the gemologist will not be much longer. Totally accurate and consistent color grading technology has to be a reality. Maybe it just needs to be refined or made more financially accessible, but that does not seem to be too hard to imagine in the relatively near future.

Yes, I do believe that using color analysis technology instead of human eyeballs would be beneficial. However, I know that there are others that believe that human graders, by virtue of looking at thousands and tens of thousands of stones over a career, are very consistent. On the other hand, I know that factors other than the color of the crystal as it comes out of the mine can influence color:
cut quality
fluorescence
shape (round vs emerald vs marquis, etc.)
variations in human visual abilities
just to name a few.

Lula, some of these questions were art least partially addressed here

[URL='https://www.pricescope.com/community/threads/can-cut-influence-colour-grading.153862/']https://www.pricescope.com/community/threads/can-cut-influence-colour-grading.153862/[/URL]

 

[Lula]

I would think the days of grading color with master stones and the eyes of the gemologist will not be much longer. Totally accurate and consistent color grading technology has to be a reality. Maybe it just needs to be refined or made more financially accessible, but that does not seem to be too hard to imagine in the relatively near future.

Yes, I do believe that using color analysis technology instead of human eyeballs would be beneficial. However, I know that there are others that believe that human graders, by virtue of looking at thousands and tens of thousands of stones over a career, are very consistent. On the other hand, I know that factors other than the color of the crystal as it comes out of the mine can influence color:
cut quality
fluorescence
shape (round vs emerald vs marquis, etc.)
variations in human visual abilities
just to name a few.

Lula, some of these questions were art least partially addressed here

[URL='https://www.pricescope.com/community/threads/can-cut-influence-colour-grading.153862/']https://www.pricescope.com/community/threads/can-cut-influence-colour-grading.153862/[/URL]

Thanks, slg! I don't venture often into the Diamond Research forum; too much math and physics and not enough drama for me So I completely missed that thread.

P.S. I loved your comment about referring to your diamond as a "Wesselton" color!