Scintillation

Very similar  to  lustre  and  brilliance,  scintillation is used to describe the optical effect  seen in gems such as Diamonds, where an area  of light on a polished facet seems to flash on and  off as either the gem or the light source moves.    I often referr to scintillation as the lighthouse  effect.    The  GIA  (Gemological  Institution  of  America),  who  invented  the  four  ‘C’s  as  a  way  of  measuring  the  quality  of  Diamonds,  use scintillation as one of the seven criteria for  assessing the quality of a gem cut.