Master stone set Diamond Color Grading

[DonaldsonsJewelers]

I am inquiring as to why natural diamonds are required for color grading with some certifications whereas CZ matched color sets are allowed for other certifications. Could someone explain why that would be?

 

[oldminer]

CZ sets are not graded by the GIA lab. They are subject to being incorrect when delivered and to further alter by fading or darkening over time. However, they can be useful for grading if the gemologist has a few control diamonds with known GIA grades to make sure nothing adverse happens to the color of the CZ's by checking their integrity frequently.

GIA is very hesitant to even make a set of Master color grading diamonds now. If they agree to do the job, you need to have a large supply of the correct quality of diamonds, have a big budget and plenty of time. New sets are extremely rare. The old sets that come to market are mostly from the 70's and 80's and the colors don't necessarily agree with GIA's current color grading by machine where there are some nuance differences with older grading.

If you can find the correct yellow color tint in Lab diamonds with GIA grading, those stones could be helpful with controlling a CZ set, but there are few Lab stones below K color. Many lab diamonds have a brown or blue tint which makes them less useful for grading typical yellow tint diamonds. Still, having some control diamonds with GIA reports with known colors is useful.

 

[Texas Leaguer]

Excellent explanation!

 

[Karl_K]

What I find interesting is that diamond masters can drift with age due to metal contamination and need to be acid boiled from time to time on top of regular cleanings..