Grading Diamonds

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Diamond Clarity Grading

Diamond Colour Grading

Diamond colour grades are alphabetical letter grades from D to Z. The highest prices charged are for D colours. Once a diamond has enough colour, it is considered a "Fancy Colour." These are graded Z+.

Diamonds are graded by comparing them to diamonds of known colour grades. The comparison diamonds are called "Master Stones."

Diamond Cut Grading

It's important to understand that cut grading is broken down into two categories of "Proportions" and "Finish." Proportions refer to the measurements of the table facet, crown angle. girdle thickness, pavilion depth and culet size. It also refers to major symmetery issues such as whether the girdle plane is parallel to the table facet. Finish is the analysis of some smaller details: polish and minor symmetry issues.

You may have heard of the "Ideal cut". This is a term that refers to the proprtions of a diamond. An Ideal cut diamond is one that is cut to "Ideal Proportions" as laid out by Marcel Tolkowski. His mathematical work determined the best proportions for a diamond to maximize brilliancy, dispersion and scintillation of a diamond. Recently, the GIA examined many thousands of diamonds and concluded that there are other combinations of proportions that deviate from the ones defined by Tolkowski which yield excellent brilliancy, etc. Today diamonds of a top quality cut grading are referred to by the GIA as "Excellent" rather than "Ideal." Excellent is a broader term that also refers to finish and minor symmetry and accepts some proportions that may have previously been outside of Ideal proportions. This is not to say the GIA has lowered any standards. It simply came to a conclusion through observation that the Ideal cut definition may have excluded a few diamond proportions which were equally as beautiful. Today, the diamond industry accepts both terms to describe a top quality cut.