Diamond Terms


The white light returned by a diamond through the crown and table of the stone.


A term that takes into account the proportions, polish and symmetry of a diamond.


The purity of the interior of a diamond defines its clarity. Any imperfection whether natural or man made located in the interior of a diamond is considered an inclusion or what used to be called a flaw.


A grade representing the degree to which the diamond has a body color. Colorless is best. In GIA (Gemological Institute of America) terms D is the highest grade. In AGS (American Gem Society) terms the highest grade is 0.


The weight of diamonds is measured in carats. One carat is equal to 1/5th of a gram.


The upper part of a faceted diamond. All that is above the girdle of a diamond.


Diamonds are frequently found in a cubic crystal structure.


The point at the bottom of a diamond.


Any diamond that has been processed in any way other than cutting and polishing to improve its appearance or durability.


The outermost edge of a cut diamond.


A set of systems based of the perfection of a diamond. It is the yardstick approach to quantify a diamond's value based on known factors of rarity, demand and overall looks. Though it is most important to understand the grading of a diamond before buying one and having an insight into how each grade affects the gem. It is not the final word when buying a diamond for it's personal appeal.

Ideal Cut

The term "Ideal Cut" has been badly misused and now there are several "Ideal Cuts." Originally, it was coined to refer to Tolkowsky's Brilliant Cut developed in 1918. It was the first cut to take into consideration the optical properties of a diamond by using theoretical calculations. Tolkowsky actually did two separate equations, one for brilliance and one for dispersion. In 1975, the American Gem Society defined Tolkowsky's cut as ideal for grading with grades based on their departure from such proportions and finish. In 1995 they gave the name ideal to their highest grades for proportion, symmetry and polish.

The first diamond to be called "Ideal Brilliant" was in 1926. It was developed by Johnson and Roesch but it failed to compare with the Tolkowsky Brilliant because they used a formula that only considered light from one angle. The term "Ideal" settled down to refer to a compromise from the original Tolkowsky proportions which cutters found too strict. Tolerances were allowed into the equations that provided a cushion for the cutters and a diamond still considerably finer in beauty and finish than the American domestic Brilliant Cut. Today, because of several reasons, including court testimony, cutters each have a right to their own "Ideal Cut." One needs to be aware of what the original formula was to appreciate the meaning of the term.


A stone made by man from material different than the natural diamond.


The appearance of a surface in reflected light.


Polish is graded from Excellent to Poor. The American Gem Society Laboratory replaces the term Excellent with Ideal. A poorly polished stone deflects light thus changing its path.


The percentages and angles that describe the measurements of a diamond. Proportion is graded by the American Gem Society from Ideal to Poor or 0 to 10. This determines the path of light through the stone and thus it's brilliance.


All that reflects from a diamond including it's reflection, brilliance and fire.

Symmetry (Asymmetry)

How well the facets line up and meet each other. In the finest diamonds, how parallel the facets across from each other are is also considered. The GIA (Gemological Institute of America) grades Symmetry from Excellent to Poor. The American Gem Society Laboratory replaces the term Excellent with Ideal. Perfect symmetry in a round brilliant cut will display the heart and arrow effect. Most of the prismatic effect comes from a diamonds symmetry.


A stone made by man from the same material as a natural diamond.


The table is the uppermost flat part of a diamond. Generally it is the largest facet on the gem.