Brilliance is a term used to quantify the brightness of a gemstone. Brightness, and therefore brilliance, are related to the surface polish on the gem and the quantity of internal light reflection. 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.
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.