The art of cutting and polishing stones as practised by lapidaries. The stone to be cut is cemented to the end of a stick, and the different facets or planes on its surfaces are formed by a little simple mill contrived for the purpose. In India the mill is made of a mixture of lac resin and emery (or corundum) by melting one part of the former, and then mixing two of the latter with it by degrees; and, subsequently, well beating and rolling the paste to give it solidity, and the required form. In this country, the soft metals, such as fine copper, or the alloys of tin and lead, are used as the substance for the mill or grinding-wheel; in the surface of which is impressed diamond dust, emery powder, or other suitable abrading or polishing powders. The mill is made to revolve horizontally. Near to the mill is fixed a thick upright peg of wood, called a guage, which is pierced with small holes in all directions, and the process of forming the facets thus takes place. The stone at one end of the stick is applied to the surface of the mill, and the opposite end of the stick is inserted into one of the holes of the guage; in this position it is kept steady by the workman with his right hand, whilst he gives motion to the mill by his left.
The skill of the lapidary is exercised in regulating the velocity of the mill, and on the pressure of the stone against it, with an almost imperceptible tendency to one or other direction in different stages of the work, examining each facet at very short intervals, in order to giving as great precision as possible to its size and form. The cutting being completed, the polishing is effected by changing the mill-wheel for another usually made of brass, the surface of which is charged with fine emery, tripoli or rotten-stone, by the successive use of which the facets are perfected and brightened.