This page provided more detailed information than is required for students of EPS2
(1) Place the UNMOUNTED stone table down on a white surface (or in a gem trough) - look through the pavillion to the table or through the pavillion.
Sometimes a color - measuring device (colorimeter) is used, more commonly, grading is done by comparison with standards.
GIA scale: D (colorless) - Z (yellowish):
Note: most engagement rings are G to H.
The following statistics provide an indication of the relationship between grade and price:
In a current listing, prices ranged from $17,000 per carat for a D to 3,400 for an M (400%). In SI clarity, the total spread was a little less than half of that, and the difference between a D and a G was about 20%.
Prices are constantly in flux, and the availability of high color is a big part of it. However, a certifiable D is a rarity. Because there are relatively few colorless diamonds on the market, the per carat price of what is known as "collector color" (D,E,F) is considerably higher than diamonds of lower color grades, all other factors being equal.
The AGS scale goes from 0 to 10:
Colorimeter scales go from 1 - 10!
GIA = E, colorimeter = 1.0 but AGS scale = 0 and colorimeter reading is 0.75!
Color of a fancy color diamond composes 60 % of its value!
Color may be:
FL - IF - VVS1 - VVS2 - VS1 - VS2 - SI1 - SI2 - I1 - I2 - I3
I = inclusions can be seen by a naked eye (need to take a look at a few of them before you will start seeing them)
Rest of the grading is done under a 10x microscope.
SI Using a microscope, you should be able to see the inclusions within about 5 seconds
VS probably takes a long time to find any inclusion on your own, assuming you are used to using the microscope.
VVS2 An expert would find it difficult to find an inclusion from the top of the stone
VVS1 An expert would find it difficult to find an inclusion from the bottom of the stone
IF internally flawless diamonds have no observable internal inclusions, only some on the surface that could be gotten rid off by polishing the diamond some more at the expense of weight.
FL diamonds are again extremely rare, there are only about four hundred 1 ct. FL diamonds produced per year worldwide.
(Source: Extracted from http://kaos.deepcove.com/cig/mlynek.html)
In the past, the eye-visibility on an inclusion was the determining factor in grading. The GIA now say that it is that the nature, size and location of an inclusion that sets the grade, not eye-visibility (or lack of it). Thus, it is now possible to have an eye-visible inclusion in an SI2.
This shift resulted in the evolution of a new clarity grade: the "SI3", not yet recognized by the GIA but in common usage world-wide. The SI3 grade is a useful way to differentiate between somewhat imperfect diamonds that face-up well and diamonds that face up poorly.