When an independent, professional gemologist evaluates a diamond, they come up with what is known as a diamond grading certificate. Value is not considered here, but rather the quality of the stone. No two diamonds are the same, as each has distinct characteristics, each of which are described in the certificate. When talking about quality, you need to talk about the 4 C’s, which are color, clarity, carat, and cut. The gemologist puts’ together a hand-drawn map on the grading certificate, with all inclusions shown. The diamond you buy should match what is shown on the certificate.
While there a many gemological laboratories out there, not all of them are respected by everyone in the diamond trade. A couple that are respected are the Gemological Institute of America (GIA) and the International Gemological Institute (IGI).
Some of the terms commonly used on diamond certificates are explained below:
Stone ID – Every diamond is given its own unique ID, with all those numbers registered and stored in a global database.
Date – As you might have guessed, this is the date on which the report was issued.
Cut and Shape – Standard round brilliant is the most common shape, with the others referred to as fancy shapes or cuts. The name of the others is dependent on their shape. Among the most popular of this group are process cut, oval emerald, marquise, heart, radiant, and per-shaped.
Dimensions – Round shapes have dimensions stated as “largest diameter – smallest diameter X depth,” while other shapes are stated as “length X width X depth.”
Carat Weight – The weight of a gemstone is measured in carats, with .200 grams equal to 1 carat. The ct. abbreviation is usually used for the weight.
Graining – The crystal structure can have irregularities reflected by graining and grain lines. White, colored, or reflective graining may affect clarity grade, whereas colorless graining does not.
Proportions – This part of the certificate pertains to the angles and measurements of a polished diamond. The optical properties of a diamond are affected by proportions more than anything else. Pavilion depth, crown angle, and table size have been shown to have a dramatic impact on the appearance of a diamond.
Depth% – In fancy shapes, this is the depth divided by the width, while it is the depth divided by the average diameter in round diamonds.
Table% – In round diamonds, divide the average size of the table facet by the average diameter. The average table facet size is divided by the width in other shapes.
Girdle – The girdle refers to the outline of the diamond on the outside edge. On the certificate, the thickness of the girdle relative to diamond size is shown. The condition of the diamond, polished or faceted, is also taken into account.
Culet – The point at the bottom of the diamond is the culet. The size of the facet relative that of the diamond will appear on the certificate if the culet is faceted.
Finish – The polish or surface condition is represented in the finish grade, as are the shape, size, and placement of the facets.
Polish – This refers to how well the diamond cutter shaped and faceted a rough stone to deliver the finished article.
Symmetry – The facets and finished angles will have a certain level of symmetry once the cutter has finished working. Diamonds are all about brilliance and fire, and both are at their best when a diamond has been symmetrically cut and proportioned. The grading on the certificate is usually referred to as Excellent, Very Good, Good, Fair, or Poor.
Cut – gain, brilliance and fire are at their best when the proportions and finish of the diamond are as they should be. When perfect proportions are deviated from, the beauty of the stone can be compromised.
Clarity – Very few diamonds are free from inclusions and blemishes. 10X magnification is used to grade diamonds from the very rare Flawless down to included. The number of inclusions, as well as size, nature, and position are used to grade clarity.
Color – Compares to Master Color diamonds to assess to an obvious Yellow (Z).
Pavillion Depth – This refers to the distance from the bottom of the girdle to the culet. If the pavilion depth is to deep or shallow, light will escape from the sides or bottom from the stone. Diamonds that are cut well will direct more light through the crown.
Tolkowsky Ideal Cut: Marcel Tolkowsky was a Russian mathematician who calculated what it would take in terms of the proportions of facets in a round diamond so that it would be perfect. The beauty of a stone becomes compromised when there is a deviation from those designs.
Fluorescence – Diamonds tend to look more white, blue or yellow when exposed to UV light, which implies that they contain a property known as fluorescence. The average person cannot see these effect with the untrained eye, which is why gemologists include fluorescence as part of a diamond certificate. This element is more about the characteristics of the stone as opposed to being a grading factor.
Crown Height – The upper portion at the top of the diamond is where you find the crown height.
Diagram – The shape and cutting style of a stone are approximated in the diagram. Nature, type, position, and approximate size of a clarity characteristic are included.
Key to Symbols – This is where, of present, the characters and symbols on the diagram are listed.
A diamond certificate put together by a professional gemologist will help ensure that you are getting value for money in the diamond you buy.