An optical effect, possessed by certain translucent gemstones in reflecting light, in which a movable, wavy or silky sheen is concentrated in a narrow band of white light that changes its position, when the gem is turned. This is a characterized of cat's
The classification of fashioned gemstones or diamonds according to their clarity using the standard nomenclature of terms: flawless, pure, clean, perfect (for top grade). VVS (very very slightly included), VS (very slightly included), SI (slightly include