How GIA grades color in colorless vs. fancy colored diamonds

[Sagebrush]

Re: How GIA grades color in colorless vs. fancy colored diam

TL, et al,

Quite right, the grade went from grayish to fancy deep. Have you seen the stone? It is blueish gray. The theory behind GIA's colored diamond system is complex and requires a secure grounding in color science. If you have Secrets please read the relevant chapters. GIA has published a book that includes all the G&G articles on this topic. I'll post the full title after I get to the office. I suggest you buy and read it if you are planning to purchase a colored diamond or give advice here. Stephen Hofer's Collecting and Classifying Coloured Diamonds is also a useful reference.

Once you have read the relevant material, I will be more than happy to answer any questions and/or discuss the issues. It would make for a very interesting thread.

Best,

 

[T L]

Re: How GIA grades color in colorless vs. fancy colored diam

This is what you say in your book, " Since gray is not considered a hue in the GTL [Gem Trade Laboratory which you refer to as GIA-GTL in other paragraphs] grading system, it was partially ignored, but only as a hue. If the gray primary hue had not been present, the stone probably would have been graded faint blue, but the saturation and tone of the gray were factored in since they contributed to the overall saturation and tone, justifying a grade of fancy blue. Thus a visually light bluish gray diamond becomes a fancy blue diamond."

Obviously GIA is now including "gray" in their color designation for some hues (blue being one of them), so is it time to update your book and make that clarification??? If I'm wrong about anything, please correct me. Gemology is changing all the time, so books can easily become outdated if one does not keep up with it. I think you only have one edition of this book.

 

[Sagebrush]

Re: How GIA grades color in colorless vs. fancy colored diam

TL & Kenny,

The book I mentioned, is Gems & Gemology in Review, Colored Diamonds, edited by John M. King. Mr. King is in charge of colored diamond grading at GIA and since the GIA certificate is the be all and end all in colored diamond grading, this is the book to read BEFORE buying a colored diamond.

I am really paraphrasing King in my explanation. The criteria have not changed. The above book was published in 2006, but the articles go back several years. GIA has a very interesting relationship with gray. The short answer is if the gray is dark enough (tonally) it will be counted. In the Wittelsbach, is a medium bluish-gray to blue-gray depending upon the light. Hofer makes the point that the GIA system was re-designed to use more attractive terms, terms more pleasing to its clients, who are gem dealers. GIA added the terms "fancy deep" in 1995.

The GIA system uses terms relative to the amount of 3-D color space a given hue occupies. Yellow is a much bigger color than blue, therefore a vivid yellow must be truly "vivid" as we understand the term. A blue diamond may be called vivid without actually being vivid because of the relatively compressed area of 3-D color space that blue occupies. Blues almost always have some gray, so a vivid blue may be a grayish blue. To me this approach is pure sophistry. Terms are turned upside down. A vivid blue is not vivid and a deep blue is not deep.



Best,

 

[LD]

Re: How GIA grades color in colorless vs. fancy colored diam

TL, et al,

Quite right, the grade went from grayish to fancy deep. Have you seen the stone? It is blueish gray. The theory behind GIA's colored diamond system is complex and requires a secure grounding in color science. If you have Secrets please read the relevant chapters. GIA has published a book that includes all the G&G articles on this topic. I'll post the full title after I get to the office. I suggest you buy and read it if you are planning to purchase a colored diamond or give advice here. Stephen Hofer's Collecting and Classifying Coloured Diamonds is also a useful reference.

Once you have read the relevant material, I will be more than happy to answer any questions and/or discuss the issues. It would make for a very interesting thread.

Best,

This has got to be THE most condescending few sentences I have ever read on this forum.