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Diamond Cut

The way your diamond sparkles comes not from the shape of the stone, but from the cut: the symmetry, proportioning, and polish. The facets cut into diamonds help them reflect light not just from the top of the stone, but from the facets along the bottom section that are angled to bounce light back up through the top of the diamond, adding radiance. (Think about light bouncing off a pane of glass when the glass is at the right angle.) This is why diamonds are cut to maximize brilliance and not size. And this is why when you go to museums and look at old jewelry, the stones often look somewhat dull: it is not because of their age that they don’t sparkle, but because the modern cutting techniques that create multiple, balanced facets to best reflect light did not yet exist.

A diamond stone looks rough and unimpressive when first mined, but then its inner beauty emerges when the diamond cutter begins cutting facets into the stone. The cut of a diamond greatly impacts a diamond's brilliance; the choice of diamond cut is decided by the rough stone’s original shape and the desired shape, the preservation of carat weight, and the location of internal flaws or inclusions.

When a diamond is cut with the proper proportions, light is returned out of the top of the diamond and adds to the light already being reflected from the top facets through the prism cut into the top--this creates the “sparkle” and “fire” of your diamond. But if the stone is cut too shallowly, light leaks out of the bottom. Too deeply, and light escapes out of the side, decreasing luminosity.

Diamond cut

The luminosity from a good cut can mean the different between a radiant, lively diamond, and a lifeless, lackluster stone that may be larger, but not as valuable. Thus, a diamond grader’s assessment of the diamond’s cut will be an integral factor in the diamond’s ultimate categorization. That assessment falls into five categories: excellent, very good, good, fair, and poor. Diamond Select does not offer any diamonds evaluated to have a “poor“ cut.

Each diamond shape (round, oval, emerald, etc.) has its own set of guidelines for what makes a Premium or Good cut. An ‘ideal cut’ is a specific set of guidelines for some shapes that delineates the proportions that give a diamond the highest amount of fire and brilliance for the select shape.

When you are searching for your diamond in the Diamond Select Ring Builder, you can narrow the “cut” categories to look through prices for diamonds assessed to have different strengths of cut from fair to excellent; Diamond Select notes that while a “fair” categorization in particular will mean that the stone will have decreased “sparkle” and “fire”, choosing a lower-ranked cut can make larger rings more affordable.

It important to note that some independent grading laboratories do not grade a diamond’s cut, while others do. Much of this depends on the diamond’s shape. The Gemological Institute of America (GIA), for example, will only give an evaluation of the quality of a diamond’s cut for round brilliant diamonds. For all other diamonds, only the shape and measurements of the stone are part of a GIA report. The report, however, will give the proportions of the diamond (depth and table percentages), girdle thickness, and culet size (if any) as well as a general rating of the stone’s finish, including its polish and symmetry. Please refer to the Diamond Anatomy education page.