Diamond Quality Assurance
Diamonds in the upper ranges of quality spectrum are often accompanied by a Diamond Grading Report from the Gemological Institute of America (GIA), a laboratory considered to be a leading international authority on diamond grading. Some diamonds are certified by other well-known laboratories, such as the European Gemological Laboratory (EGL), the International Gemological Institute (IGI), or the American Gem Society (AGS), which each have their own separate set of standards for grading.
A diamond certificate assures maximum accuracy and consistency and guarantees the stone's integrity. The certificate ensures the quality of the stone through an independent and objective laboratory of professional diamond experts. The diamond report provided describes a diamond's shape and cutting style, its proportions, finish, clarity, color grades, and symmetry. Below is a list of definitions found on the report.
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- Shape and cutting style: Shape is simply the overall outline of the diamond when viewed from the face-up position (round, oval, pear, etc). Cutting style is the type of faceting that is used to fashion the diamond (brilliant-cut, step-cut, etc.).
- Measurements: Dimensions in millimeters which the diamond has been cut. The dimensions refer to length (the longest side of the stone), then width, then the depth (height) of the diamond.
- Weight: Carat weight is the standard measure of a diamond's weight. A carat (equivalent to 200 milligrams) consists of 100 points. Therefore, a diamond of 75 points weighs .75 carats. It is important to remember that two diamonds of equal carat weight may have dramatically different values, depending upon the stone's cut, clarity, and color.
- Depth: Measured as the depth of the diamond (the distance from the table to the culet) divided into the average width.
- Table: The width of the table as a percentage of the width of the entire stone.
- Girdle: There are two criteria for the girdle; thickness and if a diamond is polished or faceted. Girdle ranges from extremely thin to extremely thick.
- Culet: This is the bottom point of the diamond. Small to very small is desired, so that it is not visible through the top of the stone.
- Polish: The brightness or luster of the stone. Polish ranges rate from excellent to poor.
- Symmetry: Describes how the facet edges of the diamond align with each other. A symmetrical stone will match exactly on all angles and facets. Excellent to poor ratings apply.
- Clarity Grade: Most diamonds contain very tiny natural characteristics called "inclusions." The size, number, position, nature, and color of these inclusions (as seen by the trained eye using a 10 power magnification) will determine a stone's clarity grade. The fewer and smaller the inclusions and surface blemishes, the more valuable and rare the gemstone.
- Color Grade: In nature, diamonds are found with a wide array of colors — from colorless, faint yellow or brown, to rare pinks, blues, greens, and other colors known as "fancies." Most diamonds have at least a trace of yellow, brown, or gray body color. In general, however, the more colorless the diamond, the greater its relative value. A totally colorless diamond allows white light to pass effortlessly through it, creating a rainbow of colors as the light is dispersed.
- Cut Grade: Some laboratories assign a cut grade for round diamonds. Cut determines the brilliance of a gemstone. Also called "make," cut refers to the proportions and finish of a polished diamond. If properly cut, the diamond will reflect light from one facet to another, to be dispersed through the top of the stone.
- Fluorescence: Indicates whether a diamond reacts to ultraviolet light. Grades range from none to very strong and may reflect colors such as blue or yellow. Some blues may actually enhance a stone's appearance because it will appear whiter in daylight or in fluorescent lighting.
- Drawings: Also called plots, the drawings represent a top and bottom view of the diamond, and show any internal or external characteristics, such as inclusions, that are present on the individual diamond.