- Joined
- Feb 26, 2003
- Messages
- 379
"I would say to be on the safe side, take GIA''s teaching that a diamond begins to ''draw color'' at G. If a VSB D color diamond stays in the D-F range that GIA calls colorless, it is safe to say it qualifies as blue-white.
If, as the more common VSB diamonds do, the color absent fluorescent stimulation drops three or more grades, the stone clearly does not qualify as blue-white. At some point (you decide) it is the ''false color'' diamond well known in the diamond trade going back before the turn of the 20th century." Michael D Cowing
Michael, I just revisited this and it should have an additional qualification - should the Fluorescence be Strong, Very Strong only, or is Medium also acceptable? Garry Holloway
Potentially, diamonds of Medium, Strong or Very Strong Blue can be blue-white.
Let''s go over what we know about blue-white diamonds from historical literature, and then use our current knowledge of diamond color grading and causes of diamond color to arrive at a modern definition and test.
From both Wade in 1916 and Bruton in the 70''s, we can see the working definition of blue-white and of those "false white" diamonds that should be excluded from this designation.
The rare, true blue-white is a term historically reserved for "a particular type of white stone … that is very slightly bluish, usually owing to its strong blue fluorescence" (Bruton, 197
. Bruton noted that the term blue-white "has been much abused," and speculated that 99% of the diamonds sold as blue-white were not only not blue-white, but had tinted yellow body color. He called the color of these diamonds "false white". In his book "Diamonds A study of the factors that govern their value" (1916), Frank B. Wade warned dealers to be "on their guard against them". He said that few bluish appearing diamonds are really blue in body color. "Most of them owe their blueness to a bluish fluorescence which becomes more marked the stronger the light. ... Some of these stones are inferior in beauty to pure white stones when viewed under a light which does not cause them to fluoresce."
From these quotes we see at least as far back as 1916 that it was known that fluorescence was the principal cause of the blue-white nature in these diamonds, and that the additional requirement for a true blue-white was that the stone not be inferior in beauty to pure white stones in light which does not cause fluorescence. Notice that in this light the diamond no longer must be blueish, only pure white, because the principal cause of it appearing blueish is absent in fluorescence de-activating light.
From this historical definition it is clear that testing must be done in two lighting environments to make a determination. The first test is reasonably well expressed in the FTC guidelines, that is: observe the diamond in normal, north daylight or its equivalent, and if the diamond shows any color or any trace of any color other than blue or bluish, the diamond is not blue-white.
A reasonable working definition of normal, north daylight is a typical sky around noon in the northern hemisphere illuminating diamond bourses such as those in Antwerp, London, New York or Israel. This is the D65 or 6500K color temperature standard. So the FTC regulation''s wording gets us half the way to our definition:
1. The diamond is observed in normal, north daylight (which has > 500uW/cm2 of UV) or its equivalent along side a faceted, colorless quartz crystal or a colorless non-fluorescent diamond, and checked to see if it is any amount more blueish.
2. If it is, we go on to perform the same comparison in lighting of similar color temperature, but one that does not stimulate fluorescence. I would employ the lighting that the AGA Task Force has recommended to obtain the "true body color" absent fluorescence stimulation. Then decide if the diamond color in this light is "inferior in beauty to pure white stones."
What was meant by pure white is not restricted to GIA''s D. Here it is helpful to reference Pagel-Theisen''s book to decide what range of GIA letter grades equate to pure white. She has done as good a job as anyone in reporting on the equating of various color grading systems to the historical terminology.
D and E equate to river, rarest white, and Exceptional White. F and G equate to top Wesselton and rare white. Most gemologists and jewelers use the working definition of colorless from GIA which calls the grades D-F colorless, with the diamond just beginning to "draw color" at G.
The case is made from these definitions that you are on very firm ground to draw the line of "inferior to pure white" between F and G, and putting the boundary between E and F is rock solid. That is why I classified Antoinette''s VS Blue 3.02 cushion as the classical example of a blue-white diamond, since its "true color" grade was E.
The importance can be seen here of having a grading light that does not stimulate blue fluorescence, thereby allowing the grading of "true body color". Without it, the rare true blue-white is lost to history, consigned to being discounted just as the "false white" diamonds with their tinted "true color" justifiably are.
If the FTC regulation had added to it the requirement that a blue-white diamond must additionally be colorless (D, E, F) in lighting that does not stimulate blue fluorescence, diamonds which pass both tests could be justifiably sold as the true "blue-white".
Why ban such an historically important designation, when it can honestly be marketed with this modern definition as a uniquely beautiful, exceptional and very rare diamond of historical importance that few possess?
Michael D Cowing
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