246 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



the diamond is specially adapted for cutting glass, and that artificially prepared edges of 

 similar construction, made of softer stones, were almost equally efficacious. He constructed 

 such edges of ruby, sapphire, quartz, &c., and while these were well adapted for cutting 

 glass, the straight edge formed by the intersection of two plane faces of a diamond was 

 found to be quite unsuitable for the purpose. 



For a glazier's diamond, a small natural crystal of suitable form, such, for example, as 

 the curved rhombic dodecahedron, or other crystal with curved faces (Fig. 31, c, d, &c.), is 

 used. This is fixed in a metal setting by a fusible alloy, with the cutting edge projecting, 

 and the whole furnished with a wooden handle. The use of the tool requii-es a little 

 practice, which needs to be acquired for each particular diamond; a slight deviation from 

 the correct method of handling the tool militates against its effectiveness. The majority of 

 the stones used in the construction of glazier's diamonds are said to come from Borneo and 

 Bahia. 



Sharp splinters of diamond, such as are often obtained in cleaving diamonds preparatory 

 to the process of grinding, are often mjOunted in a similar manner and used for the purpose 

 of drawing and writing on glass and other hard substances. Such diamond-points are also 

 useful in boring holes in glass, porcelain, precious stones, &c., and are employed now, as in 

 ancient times, in the engraving of precious stones, such as the ruby and sapphire. In recent 

 times, however, the diamond-point for engraving has been replaced by a small, rapidly 

 rotating metal disc or point charged with diamond powder and olive-oil. 



There are many purposes for which the extreme hardness of the diamdnd renders it 

 specially valuable. Thus it is used as a cutting tool in the lathe for turning the edges of 

 watch-glasses and pivots of specially hard steel, such as are used in instruments of precision 

 of all kinds ; for the boring of cannon, as, for example, in the works of Krupp at Essen ; 

 in the manufacture of the finer mechanical tools ; for boring small holes in large stones 

 through which fine gold and silver wire is drawn ; in the turning and working of hard 

 stones, such as granite, gneiss, porphyry, &c. ; for the pivot supports of the most accurate 

 chronometers and other delicate instruments, and for many other purposes. 



The diamond, however, at the present time, has a wider application in a direction 

 which has not hitherto been indicated, namely, in the construction of rock-drills. Since 

 its introduction in 1860, the diamond rock-drill has grown steadily in importance, and is 

 now widely used in the many boring operations connected with mining, tunnelling, and the 

 sinking of artesian wells, prospecting bores, &c. The rotating, boring crown of the drill is 

 studded with carbonado, and, compared with other boring appliances, penetrates the rock 

 with extraordinary rapidity. The fashioning of sharp-edged furrows on the grinding 

 surfaces of millstones, for which in recent years special machines have been devised, is also 

 effected by means of the diamond ; for these, and all other technical purposes, small diamonds 

 of poor quality, bort, and carbonado are used. 



Diamond powder is now used very largely, not only in the grinding of the diamond 

 itself, but also in the gi'inding and cutting of other precious stones, even such as are soft 

 enough to be cut with emery. The economy in time and labour, and the superiority of the 

 results attending its use, more than compensate for the increased cost of the material. The 

 same substance is also used for the purpose of slicing through hard stones, the cuttino- being 

 effected by a rotating disc of soft iron, in the edge of which are embedded fine splinters of 

 diamond. 



