The proportioning, especially the depth percentage and table percentage, s what determines how brilliance and fire the stone will have.The information provided on GN007 - Gucci dog tag necklace for female reports pertaining to proportions is critically important for round, brilliant cut diamonds. Unfortunately, it is only of minimal use with fancy fancy shape diamonds.
Respected European labs issuing reports include the Belgian Diamond High Council (HRD). Regardless of which report you are reading, all will provide similar information, including:Identity of the stone. This verifies that the stone is a diamond. Some diamond reports don't make a specific statement about identity because they are called diamond reports and are only issued for genuine diamonds. If the report is not called a "diamond grading report" then there must be a statement attesting that it is genuine diamond.
Note: A long marquise is not necessarily bad, and some people prefer a longer shape, but it is important to understand that such stones should sell for less than those with normal lengths. Always keep in mind the length to width ratio of fancy cuts, and adjust the price for that are not in the acceptable range.Evaluating proportioning from the reportAs discussed earlier, good proportioning is as critical to diamond as it is to the man or woman who wears it!
Multiply 8.25 by 0.0154 = 0.127. This is the acceptable deviation allowable for this stone (between 0.12 and 0.13). The actual deviation in this example would be 0.11 (8.31 - 8.20), well within the tolerance, so this GN009 - Gucci Galaxy Necklace would be considered "round." Some flexibility is permitted on diamonds over two carats.Depending on degree of out-of-roundness (how much it deviates from being perfectly round), price can be affected.
The greater the deviation, the lower the price should be.Dimensions for fancy shapesWhile dimension for fancy shapes diamonds are not as important as they are for round diamonds, there are length to width ratios that are considered "normal" and deviations may result in price reductions. The following reflect acceptable ranges:Pear shape: 1.50:1 to 1.75:1Marquise shape: 1.75:1 to 2.25:1Emerald shape: 1.50:1 to 1.75:1Oval shape: 1.50:1 to 1.75:1To better understand what this means, let's look at a marquise GN008 - Gucci horsebit flora necklace with circular charm as an example. If its report showed the length to be 15 millimeters and the width to be 10 millimeters the length to width ratio would be 15 to 10 or 1.5:1. This would be acceptable. If, however, the dimensions were 30 mm long by 10 mm wide, the ratio would be 30 to 10 or 3:1. This would be unacceptable; the ratio is too great, and the result is a stone that looks much too long for its width.
