By reducing the depth of a stone, its color may be lightened, and a greater “spread” is often required to bring out the color in such varieties as dark sapphires and tourmalines. Again, absorption effects must be taken into consideration, particularly with tourmaline, which shows visible dichroism. A combination of the brilliant and step cut is known as the mixed cut. Here, the upper part is brilliant cut and the lower part is step cut.
The cabochon cuts, which involve curved and unfaceted surfaces, are rarely used with transparent stones, except the carbuncle garnet. The simple cabochon has a curved top and a flat base; the double cabochon has both a curved base and crown, and the hollowed cabochon (rarely seen except with carbuncle garnets) is curved above the girdle and hollowed out below. The hollowed cabochon is a favorite form with carbuncles since transparency is increased and color lightened by its use. With cabochons, the height of the crown varies; in moonstones, it is sometimes high to increase the milky sheen. Opals, star stones, cats’-eyes, and the opaque varieties of quartz are among the stones which are always cut en cabochon. There are no facets on the surface, as with other forms of cutting.