How diamonds are graded
History
In 1952, Richard T Liddicoat, along with Lester Bensen, Joe Phillips, Robert Crowningshield and Bert Krashes began to work on a new diamond grading system which they called the diamond grading and evaluation appraisal. In 1953, they released their new system which assessed three aspects of diamonds; make, color and clarity. They took terminology used in the industry at the time and refined the definitions to produce a clarity scale by which diamonds could consistently be graded. The system at that time contained nine grades, flawless, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, and I2. The I of the I1, and I2 grades stood for imperfect.
During the 1970’s two changes were made to the system. Firstly, the internally flawless grade was added, as GIA noticed that many diamonds were being aggressively cut to remove any surface blemishes, and thereby reducing the cutting quality (make) of the diamonds. The internally flawless grade gave diamond manufacturers a choice to leave blemishes on the surface of the stone, and achieve a grade higher than VVS1. The second change made to the grading system, was the introduction of the I3 grade. This change was made in response to a growing number of diamonds of very low clarity being cut.
The last change to the clarity grading system took place in the 1990’s when the term imperfect was updated to included.
The GIA grading system today
The GIA diamond grading scale is divided into six categories and eleven grades. The clarity categories and grades are:
•Flawless category (FL) diamonds that no inclusions or blemishes are visible under 10x magnification.[2]
•Internally Flawless category (IF) diamonds have no inclusions visible under 10x magnification, only small blemishes on the diamond surface[2]
•Very, Very Slightly Included category (VVS) diamonds have minute inclusions that are difficult for a skilled grader to see under 10x magnification.[2] The VVS category is divided into two grades; VVS1 denotes a higher clarity grade than VVS2. Pinpoints and needles set the grade at VVS
•Very Slightly Included category (VS) diamonds have minor inclusions that are difficult to somewhat easy for a trained grader to see when viewed under 10x magnification.[2] The VS category is divided into two grades; VS1 denotes a higher clarity grade than VS2. Typically the inclusions in VS diamonds are invisible without magnification, however infrequently some VS2 inclusions may still be visible to the eye. An example would be on a large emerald cut diamond which has a small inclusion under the corner of the table.
•Slightly Included category (SI) diamonds have noticeable inclusions that are easy to very easy for a trained grader to see when viewed under 10x magnification.[2] The SI category is divided into two grades; SI1 denotes a higher clarity grade than SI2. These may or may not be noticeable to the naked eye.[3]
•Included category (I) diamonds have obvious inclusions that are clearly visible to a trained grader under 10x magnification.[2] Included diamonds have inclusions that are usually visible without magnification or have inclusions that threaten the durability of the stone. The I category is divided into three grades; I1 denotes a higher clarity grade than I2, which in turn is higher than I3. Inclusions in I1 diamonds often are seen to the unaided eye. I2 inclusions are easily seen, while I3 diamonds have large and extremely easy to see inclusions that typically impact the brilliance of the diamond, as well as having inclusions that are often likely to threaten the structure of the diamond.
GIA clarity grading procedure
GIA clarity grading is performed under 10x magnification with darkfield illumination. The GIA Gem Trade Laboratory, uses as standard equipment a binocular stereo microscope, that is able to zoom to higher magnifications. These microscopes are equipped with darkfield illumination, as well as an ultraviolet light filtered overhead light. When grading is performed using a 10x handheld loupe, ‘darkfield’ illumination is more difficult to achieve. The grader must use a lightsource in such a way that the base of the stone is lit from the side, and the crown of the stone is shielded from the light.
After thoroughly cleaning the diamond, the diamond is picked up using tweezers in a girdle-to-girdle hold.[4] The grader views the diamond for the first time through the table, studying the culet area of the stone for inclusions.[4] The diamond is then set down, and picked up with the tweezers in a table-to-culet hold.[4] In this position the diamond can be studied from the pavilion side, and the crown side, examining the diamond through each facet for inclusions.[4] Once a sector of the diamond has been thoroughly examined the grader rotates the diamond in the tweezer, so that the neighboring sector can be examined.[4] The grader uses darkfield lighting to reveal characteristics, and alternates to reflected, overhead lighting to ascertain whether a characteristic lies within the stone, on the stones surface, or both.[4] If the grader is using a stereo microscope, they may zoom in to a higher magnification to make closer observations of an inclusion, but then return to 10x magnification to make an assessment of it’s impact on the clarity grade.
If a stereo binocular microscope has been used, a final assessment using a 10x loupe is performed before the final judgement is made on the clarity of the stone. The grader firstly decides the clarity category of the diamond using the keywords; none (FL, or IF if blemished), minute (VVS), minor (VS), noticeable (SI), obvious (I). The decision is then made on the grade of the diamond.[4]
Grading systems by other organizations
The clarity grading system developed by the GIA has been used throughout the industry as well as by other diamond grading agencies including the American Gemological Society (AGS), European Gemological Laboratory (EGL), and the International Gemological Laboratory (IGL). These grading agencies base their clarity grades on the characteristics of inclusions visible to a trained professional when a diamond is viewed from above under 10x magnification.