How to Determine the Brilliance of a Diamond

Go to a local jeweler to look at their selection of diamonds, either set or unset, or gather and compare diamonds in jewelery you may own. It may be easier to determine brilliance on a larger stone because the surface area is larger and smaller diamonds are harder to view with the naked eye. It's also best to view stones in natural light or at least not under spotlights that can make everything sparkle.

Ask questions about the cut of the diamond. The cut refers to the shape of the gem as well as how each facet of the diamond was formed and polished. The cut is important because the cut is what influences how white light bounces out of the stone. A well cut diamond sparkles more because the light bounces back to the eye through the top of the stone. Average or poor cut diamonds bounce white light back but sometimes the light leaves at the side or even through the bottom of the stone. The bounce-back affect its dispersion.

Look at the diamond you have chosen. Move the stone from side to side to see if it sparkles. If the cut is good you should see the light dancing off the stone. If you compare this to a cut that is not ideal you can see one stone appears to have more fire within while the other is more dull or lifeless. This is scintillation. You want to see a balanced sparkle across the stone as you move it under a light.

Determine the flash of the stone. The top of every stone is made up of one large facet surrounded by smaller facets. The flat surface provides for the best view of stone's brilliance. If you see more of the flat plane of the stone, the gem provider may have cut the top or side facets incorrectly. The light should bounce back at you.

Continue to move the diamond to see the how balanced the flash is compared to the dispersion. This is called the blend of the stone. A diamond with outstanding brilliance should be balanced across the stone. If you see an equal amount of sparkle all over the stone and are able to see the many facets that make up the crown of the stone, it's a quality diamond.

Ask questions. Don't let a salesperson sell you a diamond without brilliance. A stone with nearly flawless color and clarity can look dull if the cut leaves it with little brilliance, just like a diamond can be more beautiful if the cut brings out the fire in the stone, even if the color is not of the highest grade.