The G.I.A. (Gemological Institute of America) is one of the most respected organizations that issue grading reports evaluating the quality characteristics of individual diamonds. Let’s take a look at what information is contained in such a report (also called a diamond certificate) and what these data points mean.
General Identification Information
This information is usually at the top of the grading report and contains data about the shape and measurements of the diamond as well as its laser inscription number.
The laser inscription deserves more attention as it can help you indentify a particular diamond.
This inscription is a small engraving burned on the edge of the stone and serves as a unique ID that can help match a diamond to its report.
Not all diamonds have laser inscriptions, though.
Diamond Quality Grades
The major diamond quality grades evaluated in the report are the so-called 4 Cs: The four most important quality characteristics that determine the value of a diamond.
They are as follows:
This characteristic indicates how colorless the stone is. The G.I.A. grades diamond color using letters from D (Colorless) to Z (Light Yellow).
In general, the less color in a diamond, the higher its color grade.
Clarity refers to how clean the stone looks under 10x magnification. The fewer internal defects (inclusions) and external flaws a diamond has, and the less visible they are, the higher its clarity grade.
The G.I.A. evaluates clarity using grades starting from IF (Internally Flawless) all the way down to I (Included).
The cut grade in a diamond report refers to how close the stone’s proportions are to those of the so-called ideal cut, which maximizes the brilliance and sparkle of a round diamond.
The top grade a stone can get on this characteristic is Excellent, and the lowest one is Poor.
This is a number that indicates how much the diamond weighs and is measured in carats. (1 carat equals 200 milligrams, or 0.2 grams.)
In general, since bigger diamonds are rarer, they are disproportionately more valuable than smaller ones.
The information in this section gives more detail as to the features of the diamond.
Although not considered as critical as the 4 Cs, these data points provide more depth and can help you get a better understanding of the stone’s characteristics.
This characteristic refers to how smooth the stone’s polished surface is. The top grade for polish is Excellent, and the surface of well polished diamonds lets light enter them unobstructed, contributing to their enhanced brilliance.
Diamonds whose polish is graded Poor, on the other hand, have visible lines from the polishing process on their facets. These surface imperfections can reduce the amount of light that enters the stone and is reflected by it, resulting in diminished brilliance.
Diamond symmetry is a measure of how well aligned the facets of a stone are. The highest grade for this characteristic is Excellent.
Some of the imperfections that result in diminished symmetry are an off-center bottom or top of the stone, a wavy girdle (the edge of the stone), a stone’s top that is not parallel with the girdle, and irregularly shaped facets.
Most diamonds have some asymmetry, but it becomes clearly visible in stones with a Fair or Poor symmetry grade.
The grade on this characteristic indicates whether a diamond fluoresces when lit with ultraviolet light. If the diamond does not exhibit such an effect, the report will list that the stone has no fluorescence.
If the stone fluoresces, the report will indicate how visible the fluorescence is (e.g., faint or strong).
A G.I.A. report includes a diagram of the diamond (top, bottom, and side view) that shows the arrangement of the stone’s facets and the location of its visible inclusions.
You can use this figure as a map that indicates the most important “birthmarks” of the diamond.
The diagram also shows the proportions of key parts of the diamond (e.g., the diameter of the stone’s top as a percentage of the girdle). These values are important as they indicate how closely the stone’s proportions are to those considered ideal.
Two important features mapped on a diamond’s diagram are the stone’s culet and girdle.
Culet: You can see this diamond part indicated on the side-view diagram. The culet is the bottom facet of the stone.
A diamond can have no culet at all, and some people think that a missing culet makes the pointed bottom of the stone more likely to break. If a culet is present, the report will indicate how big it is.
The most preferable size for this bottom facet is small to medium; if the culet is too big, it becomes easily visible from the top of the stone.
Girdle: This is also a diamond part indicated on the profile diagram and refers to the edge of the stone. The diagram will show how big the girdle is and whether it is faceted.
If this part is too thin, it could break easily. If, on the other hand, the girdle is too thick, it will distort the proportions of the stone to some extent.
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