The Professional Gem Sciences (PGS) gem grading laboratory in Chicago wants to use the term “blue-white” on its grading reports for D or E colorless diamonds that have “very strong blue” fluorescence. “Blue-white” hasn’t been used for decades because the Federal Trade Commission says it’s unfair practice to use the term unless a diamond shows blue or bluish color. PGS appears to be challenging that ruling, since the body color of a diamond receiving the blue-white grade is colorless.
To prevent an FTC challenge, PGS says it will place the new grade in a category called “Color Appearance,” which will include a Munsell color notation. (Munsell is a standard descriptive color system.) Colorless diamonds with very strong blue fluorescence often do appear bluish in daylight.
Some diamonds with very strong blue fluorescence have been described as appearing “cloudy” or “oily” in daylight because of their extreme sensitivity to ultraviolet fluorescence. While many of these “over blues,” as they are called, do have a cloudy appearance, some do not. Diamonds that have the designation “very strong blue” listed on diamond grading reports are typically discounted in price.
As for the term “white,” the FTC doesn’t address it. Stephen Hofer, in his book Collecting and Classifying Coloured Diamonds, states that “white” is applied only to diamonds that exhibit a milk-white inherent body color that can be seen in all directions. “White” is a color, whereas colorless diamonds have no color. PGS justifies the use of the term “white” for colorless diamonds with the following explanation: “… a transparent diamond … appears white when you turn it over and view it face-up with all its radiant brilliance.” Professional Gem Sciences has been examining the grading of fluorescent diamonds and face-up appearances for several years.