Thanks very much for building this great website and your helpful contributions elsewhere. I notice on Reddit you mention blue hue a lot. So my question is, in your experience, do blue hue diamonds receive a higher letter grade for equivalent color saturation (CIE C*) in comparison to yellow hue diamonds? This could be the case if a grader has a Cape series master set and is grading “whiteness”. On the other hand, at least GCAL is explicit that they grade by saturation and try to ignore hue. So what would you say is the deal on letter grade vs C* vs hue angle?
From what I’ve seen, I don’t think blue receives a higher color grade (at least not compared to the variance within each grade for IGI). Although I’m not completely sure or have any real data to back it up.
For naturals, there is a separate set of master stones for brown (https://www.gia.edu/doc/Coloring-Grading-D-to-Z-Diamonds-at-the-GIA-Laboratory.pdf). Quoting: “Some observers try to grade just as they would yellow diamonds, and only look for saturation differences (the “amount” of yellow), which can result in an incorrectly high determination compared to laboratory grading. If yellow master stones are the only ones available, the observer should assess the overall depth of color and equate it to the overall depth of the yellow master stone.”
Do you have a link to the GCAL description? Grading saturation only seems contrary to what GIA has described to avoid what you’re suggesting about “incorrectly high determination.”