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How We Grade Diamonds and Colored Stones |
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How a diamond has been cut, polished, and to what proportions and symmetry, are of the utmost importance since these factors determine the life, brilliance, dispersion and scintillation of a diamond. If these cutting factors fall below standard, the appearance of the diamond will be adversely affected.
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The weight of a diamond is measured in carats. A carat is 0.2 grams and there are 100 points (or 200 milligrams) per carat. With an accuracy of 1/10,000 ct, the IGI scales provide a highly precise diamond weight (official weight) and this weight is specified on the Diamond Report to two decimal points. |
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weight of a diamond is measured in Carats. The IGI scales measure
with an accuracy of 1/10,000 CT |
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In order to grade the clarity of a diamond, it is necessary to observe the number and nature of any internal characteristics in the stone as well as their size and position. This analysis is carried out using a stereo zoom binocular microscope and a loupe 10x under the experienced eye of laboratory gemologists. A diamond is said to be "Internally Flawless" when it presents no internal inclusions under 10x magnification. |
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Among other criteria, the
Clarity of a diamond is determined using a stereo zoom binocular microscope
under a strict |
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Internally Flawless |
Very Very Slightly included |
Very Slightly included |
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Free from internal inclusions visible under 10x magnification (small external details tolerated). |
Inclusions and/or external blemishes very difficult to locate under 10x magnification. |
Inclusions and external blemishes difficult to locate under 10x magnification. |
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Slightly included |
Included 1 |
Included 2 |
Included 3 |
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Inclusions and external blemishes easy to locate under 10x magnification. |
Inclusions and external blemishes visable to the naked eye. |
Inclusions and external blemishes easy to locate with naked eye. |
Heavy inclusions located very easily with naked eye. |
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Most diamonds of gem quality vary in shade from colorless to shades yellow or brown. To determine the color, all submitted diamonds are compared to an internationally accepted master set of diamonds, the color of which ranges from D, or colorless (the most sought-after) to Z, light yellow or light brown. Well saturated colors occur in diamonds such as brown, orange, pink, blue, etc. The most intense of these shades are determined as "Fancy" colors and graded as such on the IGI Diamond Report |
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All diamonds submitted for color analysis are
compared with an internationally accepted master set of stones. |
Fluorescence is the phenomenon through which
ultraviolet light, invisible to the naked eye, is converted into visible light. |
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IGI |
CIBJO |
IDC |
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Colorless |
D |
Blanc Exceptionnel |
Exceptional White+ |
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E |
Exceptional White |
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F |
Extra Blanc |
Rare White+ |
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Near Colorless |
G |
Rare White |
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H |
Blanc |
White |
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I |
Blanc Nuancé |
Slightly Tinted White |
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J |
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Faint |
K |
Blanc Légèrement Teinté |
Tinted White |
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L |
Teinté |
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M |
Tinted |
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Very Light |
N |
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O |
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P |
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Q |
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R |
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Light |
S |
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International Gemological Information A Division of International Gemological Institute 589 Fifth Avenue, New York, NY 10017 Phone: 212-753-7100 www.igiworldwide.com Email: info@igi-usa.com ©2001
International Gemological Institute,Inc. All Rights Reserved. |
