84 CARBON. 



but in China and India, the art of cutting appears to have 

 been known at a very early period. 



By the above process, diamonds are cut into brilliant, rose 

 and table diamonds. The brilliant has a crown or upper 

 part, consisting of a large central eight- sided facet, and a 

 series of facets around it ; and a collet, or lower part, of pyr- 

 amidal shape, consisting of a series of facets, with a smaller 

 series near the base of the crown. The depth of a brilliant 

 is nearly equal to its breadth, and it therefore requires a 

 thick stone. Thinner stones, in proportion to the breadth, 

 are cut into rose and table diamonds. The surface of the 

 rose diamond consists of a central eight-sided facet of small 

 size, eight triangles, one corresponding to each side of the 

 table, eight trapeziums next, and then a series of sixteen tri- 

 angles. The collet side consists of a minute central octagon, 

 surrounded by eight trapeziums, corresponding to the angles 

 of the octagon, each of which trapeziums is subdivided by a 

 salient angle into one irregular pentagon and two triangles. 

 The table is the least beautiful mode of cutting, and is used 

 for such fragments as are quite thin in proportion to the 

 breadth. It has a square central facet, surrounded by two 

 or more series of four-sided facets, corresponding to the sides 

 of the square. 



Diamonds have also been cut with figures upon them. As 

 early as 1500, Charadossa cut the figure of one of the 

 Fathers of the church on a diamond, for Pope Julius II. 



Diamonds are employed for cutting glass; and for this 

 purpose only the natural edges of crystals can be used, anc 

 those with curved faces are much the best. Diamond dust 

 is used to charge metal plates of various kinds for jewelers, 

 lapidaries and others. Those diamonds that are unfit for 

 working, are sold for various purposes, under the name of 

 bort. Fine drills are made of small splinters of bort, which 

 are used for drilling other gems, and also for piercing holes 

 in artificial teeth and vitreous substances generally. 



The diamond is also used for lenses for microscopes. 

 When ground plano-convex, they have but slight chromatic 

 aberration, and consequently a larger field, and but little loss 

 of light, compared with similar lenses of other materials. 

 They often have an irregularity of structure when perfectK 



What are the three forms usually given the diamond 1 For what 

 purposes are diamonds used ? 



