2G DIAMOND 



into 8 trapeziums, each of which is again subdivided by a salient anglo (whose apox 

 touches the girdle) into one irregular pentagon and two triangles. 



To fashion a rough diamond into a brilliant the first step is to modify the faces of 

 the original octahedron, so that the plane formed by the junction of the two pyramids 

 shall bo an exact square, and the axis of the crystal precisely twice the length of one 

 of the sides of the square. The octahedron being thus rectified, a section is to be 

 made parallel to the common base or girdle, so as to cut off ygths of the whole height 

 from the upper pyramid and T T s th from the lower one. The superior and larger }>l:mo 

 thus produced is called the table, and the inferior and smaller one is called the 

 collet; in this state it is termed a complete square tabU diamond. To convert it into 

 a brilliant, two triangular facets are placed on each side of the table, thus changing 

 it from a square to an octagon ; a lozenge-shaped facet is also placed at each of the 

 four corners of the table, and another lozenge extending lengthwise along the whole 

 of each side of the original square of the table, which, with two triangular facets set 

 on the base of each lozenge, completes the whole number of facets on the table side 

 of the diamond : viz. 8 lozenges and 21 triangles. On the collet side are formed 

 4 irregular pentagons, alternating with as many irregular lozenges radiating from 

 the collet as a centre, and bordered by 16 triangular facets adjoining the girdle. The 

 brilliant being thus completed, is set with the table side uppermost, and the collet 

 side implanted in the cavity made to receive the diamond. The brilliant is always 

 three times as thick as the rose diamond. In France, the thickness of the brilliant is 

 set off into two unequal portions ; one third is reserved for the upper part or table of 

 the diamond, and the remaining two-thirds for the lower part or collet (culasse). The 

 table has eight planes, and its circumference is cut into facets, of which some are 

 triangles and other lozenges. The collet is also cut into facets called pavilions. It 

 is of consequence that the pavilions lie in the same order as the upper facets, and that 

 they correspond to each other, so that the symmetry be perfect, for otherwise the play 

 of the light would be false. 



Although the rose diamond often projects bright beams of light in more extensive 

 proportion than the brilliant, yet the latter shows an incomparably greater play, from 

 the difference of its cutting. In executing this, there are formed 32 faces of different 

 figures, and inclined at different angles all round the table, on the upper side of the 

 stone. On the collet (culasse) 24 other faces are made round a small table, which 

 converts the culasse into a truncated pyramid. These 24 facets, like the 32 above, 

 are differently inclined and present different figures. It is essential that the faces of 

 the top and the bottom correspond together in sufficiently exact proportions to multi- 

 ply the reflections and refractions, so as to produce the colours of the prismatic 

 spectrum. 



DIAMONDS, CUTTING OF. Although the diamond is the hardest of all known sub- 

 stances, yet it may be split by a steel tool, provided a blow be applied ; but this re- 

 quires a perfect knowledge of the structure, because it will only yield to such means 

 in certain directions. This circumstance prevents the workman from forming facets 

 or planes generally, by the process of splitting ; he is therefore obliged to resort to 

 the process of abrasion, which is technically called cutting. The process of cutting is 

 effected by fixing the diamond to bo cut on the end of a stick, or handle, in a small 

 ball of cement, that part which is to bo reduced being left to project. Another 

 diamond is also fixed in a similar manner ; and the two stones being rubbed against 

 each other with considerable force, they are mutually abraded, flat surfaces, or facets, 

 being thereby produced. Other facets are formed by shifting the diamonds into 

 fresh positions in the cement, and when a sufficient number are produced they are fit 

 for polishing. The stones, when cut, are flxed for this purpose by imbedding them in 

 soft solder, contained in a small copper cup, the part or facet to bo polished being loft 

 to protrude. 



A flat circular plate of cast iron is then charged with the powder produced during 

 the abrasion of the diamonds ; and by this means a tool is formed which is capable of 

 producing the exquisite lustre so much admired on a finely-polished gem. Those 

 diamonds that are unfit for working on account of the imperfection of their lustre or 

 colour, are sold, for various purposes, under the technical name of Bort. Stones of 

 this kind are frequently broken in a steel mortar, by repeated blows, until they are 

 reduced to a fine powder, which is used to charge metal plates of various kinds, for 

 the use of jewellers, lapidaries, and others. Bort, in this state of preparation, is 

 incapable of polishing any gems ; but it is used to produce flat surfaces on rubies and 

 other precious stones. 



Fine drills are made of small splinters of bort, which are used for drilling small 

 holes in rubies, and other hard stones, for the use of watch-jewellers, gold and silver 

 wire-drawers, and others who require very fine holes drilled in such substances. 

 These drills are also used to pierce holes in china, where rivet* are to be inserted ; 



