ABSTRACT

With the possible exception of a few gems, such as pearl* and occasionally amber, most of our organic and inorganic gem materials have their appearance enhanced by some form of shaping or polishing. With translucent or opaque stones this may be as basic as an abrasive tumbling operation to develop a smooth and lustrous surface while retaining the baroque profile of the original rough material. Alternatively, stones of this type may be cut in the rounded cabochon form (Figure 19.1) to bring out their surface colour or banding as with malachite and agate. Another use of the cabochon style is to emphasize subsurface sheen features such as chatoyancy and asterism (i.e. in cat’s-eye stones such as quartz and chrysoberyl, and star stones such as ruby and sapphire). If the stone is translucent but dark, the cabochon can be shallow cut to lighten the colour. Sometimes the back of a cabochon is hollow cut to produce the same effect.