The intense sparkles in a diamond as it moves are ‘scintillation’. Black and white sparkles of scintillation show well in flood lit or office lighting environments where fire can be totally absent. Under pin point or spot lights fire also adds to scintillation. Ideally a diamond has many pleasing flashes spread across the surface of the stone, with few dull dead patches.
Fire is dispersed light that appears as flashes of rainbow colors.
Brilliance is an essential attribute of a beautiful diamond and has two components; brightness and contrast. Bright diamonds return lots of light from the surroundings back to a ‘face up’ an observer.