Since it goes down to Z (OK, with some grades being broader than others and expressed as a range), and it does not skip any letter, why start at D and not A?

Ok you got me curious - this is what I found:

Why does the GIA color grading system start at D? Before GIA introduced the GIA D-Z Color Grading Scale, a variety of other symbols were loosely applied throughout the industry. Not only were A, B, and C used without clear definition, but some dealers, taking a cue from the poultry business perhaps, started grading their diamonds double A (AA).

Other systems used numbers-both Arabic (0, 1, 2, 3) and Roman (I, II, III). Most dubious of all were systems that relied on descriptive terms like "gem blue" or "blue white." Terms like these are notoriously susceptible to misinterpretation.

So the creators of the GIA Color Scale wanted to start fresh. They wanted symbols that would not have any association with earlier systems. Thus the GIA scale starts at the letter D. There may be some people still clinging to other grading systems, but no other system has the clarity and universal acceptance of the GIA scale.

OMG!

That was one of the questions in a Survivor quick fire round. I'd forgotten the anawer too.

Jen

Easy 
D is for dazzling
E is for electric
F is for fizzing
G is for glorious
H is for heavenly
I is for irresistible
J is for just right
K is for krushed ice
L is for luminous
M is for memorable
N is for nice ( very )
O is for Ooooooh
P is for pizazz
Q is for quintessential
R is for regal
S is for sizzling
T is for terrific
U is for unbelievable
V is for vibrant
W is for Wow
X is for xtraordinary
Y is for Yessssss
Z is for zingy

That`s all the diamond grades as declared by yours truly so whichever grade is your diamond, it`s FABULOUS

David says my 2.06 "unbelievable vibrant radiant elizabeth's taylor diamond" (phew that's a mouthful) ring will be ready Monday.   

Elizabeth
That`s great news and it will be fabulous !
Lynne

Now the UPS tango begins!!!!!!!!

...mmmm. As far as I know, Master Stones are graded to be the "most color allowable" for a grade. So anything which is "more colorless" than a D master stone (diamond gas?) is a D by definition. I've never seen anyone offering "D+" or "high D", though generally Golconda stones are reputed to be very white. Willing to be proven wrong...

From Richard W. Wise:  http://gemwiseblogsp...olconda-diamond.html

Modern scientific analysis has shown that many famous high quality diamonds such as the Cullinan, Regent (image: at top of page) and The Koh-I-Noor that can be proven to come from the Golconda area are of a specific type of rare, almost pure diamond known as Type IIa. Less than 1% of the world’s diamonds are Type IIa. Scientifically speaking, Type IIa diamonds are diamonds that conduct electricity and contain no significant amount of nitrogen in the diamond crystal lattice.

From the GIA:  http://www.gia.edu/n...letter_details.cfm#3

Type IIa diamonds   (relatively rare) are composed of almost pure carbon with no detectable amounts of nitrogen using a "conventional" infrared spectrometer. Modern, more sensitive infrared spectrophotometers could detect the small amounts of nitrogen–on the order of 10 parts per million–in some of these diamonds. The famous Cullinan rough (3,106 ct), with its irregular crystal shape and colorless body color, is typical for type IIa diamonds. Sometimes, type IIa diamonds may appear light gray or light brown due to crystal deformation. These particular diamonds are the type IIa diamonds that can be processed by high pressure and high temperature (HPHT) to “decolorize” the diamond. Colorless synthetic diamonds can be type IIa, because they lack the nitrogen impurity. Type IIa diamonds are transparent to short-wave ultraviolet radiation, which means short-wave ultraviolet radiation will transmit through the diamond. Type IIa diamond testers have been developed based on this property.
 
Type IIb diamonds (relatively rare) contain boron atoms, which substitute for carbon in the atomic lattice. (The amount of boron can be a few parts per million or less.) This causes absorption of the red and orange wavelengths in the visible spectrum, creating a blue color. Often their color shows a gray component and sometimes these are "pure" gray in color. The boron also makes the diamonds electrically conductive. A unique feature of type IIb diamonds is that they phosphoresce after being exposed to short-wave ultraviolet radiation. The boron also gives a distinct spectrum over the mid-infrared range, which is very different from the other diamond types. The most famous type IIb diamond is the Hope diamond, on display at the Smithsonian Institute in Washington, D.C.