Sidney Thomas Diamond Standards

To ensure that you get the most beautiful diamonds, Sidney Thomas adheres to the strictest diamond grading standards. The GIA (Gemological Institute of America) is the leading source for diamond standards, applying the most stringent standards to diamond quality. Sidney Thomas uses the GIA standards in grading our diamonds.

Don't Be Fooled

Other labs have adopted their own standards for diamond quality, but are not as strict as ours. When buying diamonds, especially online, be aware of the diamond quality that you are getting and the standards by which your diamond is graded.

The Clear Truth on Diamond Color & Clarity

The GIA diamond color-grading scale begins with the letter D (note there is no A, B or C) and descends to Z. Diamonds are given a letter grading based on how close they are to colorless. A diamond graded D will be colorless. The less color the more valuable the diamond. Sidney Thomas diamonds will always be graded on the GIA color scale. As you can see from this chart, sometimes other sellers will give their diamonds a color grade one to two entire shades higher than the GIA standard. Be informed with the clear truth about the diamonds you are buying!


Diamond clarity refers to the number and size of the natural inclusions in the diamond. The fewer and smaller the inclusions, the more valuable and rare the diamond. Sidney Thomas uses GIA standards for diamond clarity when grading its diamonds. Sidney Thomas carries a full range of diamonds and selects the stones most appropriate for the design of the piece.

The Sidney Thomas Guarantee

Sidney Thomas hand-picks only the most brilliant and well-matched diamonds. Our standards are the highest of all jewelers. We have highly trained gemologists on staff to inspect and grade all of our diamonds. Sidney Thomas stands by our diamonds and we offer a 100% money back guarantee on every diamond that we sell.