As we have noted, stones are very seldom used in their natural form. They need shaping and polishing to bring out their full beauty, and each stone of value has to be considered individually.
If we examine any transparent gem stone which has been cut, a number of small faces, or facets, will be observed covering the surfaces. Such facets have not been ground on the stone in any haphazard manner. They are there for a purpose, and in the case of diamond, their number, their proportion to each other, and their mutual inclination should be mathematically exact if the utmost beauty of the specimen is to be revealed. With other stones, the proportion of the facets to each other and also their direction are of great consequence.
Generally, transparent white stones are so cut that their dispersive powers and their sparkling brilliance are shown to the best advantage. Colored stones are fashioned so as to bring out the full beauty of the body color, their fundamental color being, as a rule, their greatest attraction. There is seldom any advantage in faceting an opaque stone, while others possessing peculiar internal effects, such as asterism, have to be considered individually.