Diamond's brilliance and luster are two of its most valued attributes. The science behind such phenomena is diamond's great ability to refract light; that is, to bend or slow light as it passes through it. The amount that a substance can impact light in these ways is quantified in its refractive index.

Science postulates the speed of light in a vacuum to be about 186,000 miles per second. But the velocity of light is slowed whenever it is forced to interact with the electrons of a substance, whether it's a liquid, gas or solid. Generally speaking, higher density materials have greater concentrations of electrons and therefore greater capabilities to refract light. Light passing through diamond is reduced to about 77,000 miles per second--near the maximum for any transparent substance.

Reflectance, or the amount of light reflected from a transparent substance, can also be inferred from a material's refractive index. Once again, diamond displays the maxim amount of reflectance for a transparent substance, displaying what is called an "adamantine" luster.

SCIENCE FACT:
Refractive Index = cv /cs
where cv is velocity of light in a vacuum,
and cs is that in the substance