In relation to a gemstone, brilliance is a term used to express the brightness of the stone. Brightness, and therefore brilliance, are related to the surface polish and the internal reflection of light. Correctly placed facets will reflect the light back to the viewer, that, in combination with the index of refraction and the polish, determine a stone's brilliance. Incorrectly placed facets can cause reflections of other facets or internal characteristics and dead spots where no light is reflected.

Sources

McNeil, Donald S. Jewelers’ Dictionary, Pennsylvania: Chilton Company, 1976. Pp. 31.

Newman, Harold. An Illustrated Dictionary of Jewelry, New York: Thames and Hudson, 1981. Pp. 48.