242 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



and, like the smallest roses, are used to form a setting round a large gem (carmoizing). 

 Very thin laminse of diamond are ground down, polished on both sides, and the edges 

 famished with small facets ; they are then used to cover small miniatures set in rings, &c., 

 producing a very striking effect, and are now known as portrait-stones or brilliant-glass. 



A few trade expressions made use of by jewellers may be explained here. Very small 

 diamonds are referred to as salt-grains, very large ones as solitaires, nonpareils or paragons. 

 All cut diamonds exceeding 50 carats in weight were formerly known as solitaires, while 

 those exceeding 100 carats have been referred to as majestic diamonds. Stones weighing 

 less than a carat are known as carat-goods, those of 1, 2, &c., carats as carat-stones, two- 

 carat-stones, &c. 



2. DIAMOND-CUTTING. 



The general principles of the art of gem-cutting have been already considered ; the- 

 cutting of the diamond, however, on account of the perfect cleavage and enormous hardness, 

 of the stone, requires special methods, which must be separately considered. 



As we have seen, diamonds are most frequently cut in the brilliant form, which form is, 

 comparable to that of an octahedron of which two opposite corners have been truncated.. 

 A truncated octahedron, therefore, can be transformed into a brilliant by simply adding the. 

 necessary facets, hence the form of crystal which can be most conveniently oit as a brilliant, 

 is the octahedron. Crystals of the form shown in Fig. 31, n and o, are therefore specially 

 suited for the fashioning of brilliants. The rhombic dodecahedron and the hexakis-octa- 

 hedron (Fig. 31, c and d) are also suitable ; but stones, whose form differs widely from that, 

 of the regular octahedron, for example Fig. 31, e and ./; cannot be so easily transformedi 

 into brilliants. Before such a stone is faceted it is reduced by cleavage to the octahedral 

 form, in order to avoid the tedious process of grinding away portions which need to be- 

 removed. The property of cleavage then is very useful to the diamond-cutter, for not only 

 is he spared much labour in grinding, but the fragments removed by cleavage can be utilisedi 

 in the fashioning of smaller gems ; moreover, the property can be made use of for the- 

 purpose of removing the faulty portions of a stone or of dividing a large stone of unsuit- 

 able form into several smaller ones. The operation is, however, one which demands the 

 greatest care ; the worker should be capable not only of detecting the direction of cleavage- 

 from the outward form of the rough diamond, but also of recognising the existence of twin-- 

 ning in a crystal. Any attempt either to cleave a twinned crystal or to cleave an ordinary 

 stone in a wrong direction, will probably be attended with more or less complete fracture 

 of the stone. 



The operation of cleaving a diamond, which is entrusted to trained workmen, is 

 performed in a manner now to be described. The stone to be cleaved is fixed to the end of' 

 a rod with some kind of cement, such as a mixture of shellac, turpentine, and the finest 

 brick-dust, and in such a position that the direction of cleavage is parallel to the length of' 

 the rod. A second diamond with a projecting edge is fixed to a similar rod with the edge 

 uppermost. By grinding the sharp edge of the second diamond against the first, a nick in 

 the direction in which the stone is to be, cleaved is cut to a sufficient depth. The rod. 

 supporting this diamond is set on a firm elastic base, a sharp, strong chisel is placed in the- 

 proper direction in the nick, and the cleavage effected by dealing the chisel a single sharp, 

 blow with a hammer. The cement may be loosened by heating, and the stone placed in 

 another position if it is desired to cleave it in another direction. The powder produced 

 when the nick is made is caught in a small box provided with a sieve, and, is utilised in the- 

 process of grinding. 



