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Diamonds are assigned color grades by comparing them to diamonds with color grades which have been certified by GIA as master
color comparison diamonds. The color grade of a diamond is determined by arranging the GIA master color comparison diamonds about one half inch apart, the lightest on the left and the others on the right in order of increasing
darkness To accurately determine color, a diamond must be completely free of all dirt and oil. A diamonds color is best observed when viewed through the pavilion in the table-down position on a flat white diamond grading trough
with line of sight parallel to the girdle plane.
A diamonds color grade is determined by moving it along the row of masters comparison guide diamonds until one seems to match. It is then placed on the side of the master, and then on the other side and compared carefully. If the diamonds color tone is lighter than the master, the next highest color grade is assigned. If the diamond is the same or only slightly darker, the grade of the master comparison guide diamond is assigned. To attain the most accurate analysis of a diamonds color it is recommended that a diamond be color graded in a white color free environment. Color grades are most accurate when evaluated in a darkened room using only the correct light source. Filtered, cool white, balanced fluorescent light is best; unlike sunlight, it is nearly free of ultraviolet light. The GIA GEM Diamond Lite is probably the best color grading light.
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