Articles about Diamond Grading
Garry Holloway1 was the first to suggest a meaningful explanation for this: he suggested that, because there is a small difference between pavilion main & half facet slopes (less than 2º in a typical round brilliant), this may cause one to be dark when the other is bright – producing contrast in the gem’s image. Studies of human optical response2 say that this is attractive to viewers; it may be why the people Tolkowsky polled chose the proportions they did.
Diamond clarity grading involves assessing how readily visible the inclusions are in a diamond and accounting for an extensive list of potential variables including the size, number, type, location, and relief of its inclusions. At the American Gem Society Laboratories (AGSL), clarity grading begins once color grading is completed.
A diamond’s color (or lack thereof) is a critical aspect in determining its market value. Grading the color is therefore a crucial part of the laboratory certification process. The following article will illuminate the various steps and considerations in performing color grading at the AGSL.