Diamond Colour Grade

[FB.]

Some diamond colour grades have quite a narrow range of colour within them, while others are quite broad.
Does anyone know why the colour grades don''t have equal increments?

Thanks,

 

[Rockdiamond]

Great question FB!

I deal with this every day as the grades do widen as stones have more color.
If we use a "graphic representation" it would look like this:

The "width" of "D" color is one inch.
"E" color is 1.15inches.
By the time we get to J color it''s about 3 inches.
Fancy Light Yellow , by these standards, is about a foot wide. For these reasons, a Fancy Light Yellow at the darkest end of the grade will generally be darker than the lightest "Fancy Yellow ( next darkest grade)

Maybe the reason is so that we don;t have 150 grades where about 25 now exist.

 

[FB.]

I can see a reason why not to have too many grades, but why did GIA create grades that were not equal in their spread of colour?

Is it a logarithmic scale?

Is it logarithmic, but with a few narrow colour bands as "break" points between certain levels of tint.
I believe that I colour is a narrow band, which also used to be known as "commercial white", whereas H colour was known as "white".

 

[Rockdiamond]

My experience is that the scale is consistent- the darker the color, the wider the grade.
I believe this was done as it correlates with physical reality,
The darker the shade, the more variations exist within that shade.
Something we''d consider "Bright white" has a lot less variation than something slightly tinted.

 

[HVVS]

I color range is narrower

Somebody showed me that thread, where there''s a post that says that the I color range is narrow.