DIAMOND-CT:7=G. The art of diamond-cut ting was not developed until the middle of the fifteenth century, although crude methods of polishing were in use long before that time. About 1470 a guild of lapidaries was established at Bruges, under the direction of Louis de Ber quem, who is thought to have been the first to devise a regular plan for the arrangement of facets. so as to increase the color effects in gems. Other guilds were soon founded in Antwerp and Amsterdam, and these cities rapidly gained pre eminence in the industry, a position they still maintain. London. the market for rough stones, is a small competitor, while Paris and New York are unimportant, except for the sale of gems.
In diamond-cutting, the operations are per formed with the single object of producing the most valuable gem from a crude stone. The apparatus used is simple. but its manipulation requires both skill and experience. In the first place, the stone must he examined carefully to determine its shape, color, and the possible pres ence of flaws. these features will govern the operation of cutting. If the shape is such that it cannot he reduced readily to one of the usual forms, the stone may be divided into two or more parts by taking advantage of the natural cleavage. The diamond is cemented to a wooden holder and a steel blade is applied in a direction parallel to an octahedral face. A sharp blow upon the back of the blade is sufficient to accom plish the cleaving. The next process (brut ing ) brings out the facet s. Two rough st ones, fixed at the end of holders, arc held in either hand of the operator, who presses them against each other, at the same time giving them a rubbing motion. The friction wears away the surfaces gradually until they coincide in position to two of the facets. The diamonds are then cemented in new positions, and the operation is continued. The waste particles of dust are collected and used in the final process of polishing. For this
the apparatus consists of a small disk of spongy cast-iron, turning on a vertical spindle at a speed of 2000 to 3000 revolutions per minute. The stone. imbedded in the apex of a metallic (lead-tin) cone is held by a clamp against the surface of the disk, which is smeared from time to time with a mixture of olive oil and diamond dust. This operation requires constant atten tion, as the stone may be permanently damaged by over-beating.
Of the several forms in which diamonds are cut, the brilliant is the favorite. It is derived from the fundamental octahedron and requires. when perfect, 5S facets. in the middle is an octagonal facet called the 'table,' which is sur rounded by 32 smaller facets, reaching to the line of union (girdle) between the upper and lower portions. On the lower portion there are 24 facets symmetrically arranged around the 'mkt.' The rose form is used for thin stones. It consists of a number of triangular facets, the apices of which meet in the crown. and whose bases are supported by a second row of facets extending to the girdle. The lower part is per fectly flat. In the briolctte the stone is cut into triangular facets, but the form is pear-slin pelt and there is no girdle.
Rint.mottAPH Y. Kunz. (Ions Prceinns ,Stow 's I NTew York. 19001 ; St reeler, r(.9 S'IoneR and G MS (London, 1894) ; St reeler, The arra! Din mondq of the World IT .ondon. I5521 ; Church, Precious St6nes (London, 1583) ; Latmay. Lis (1 inht,o1 ls (I cap (Park 1897) ; Beaumont, /',/not on it ..tourniy to the Diamond to Hs 0/ Minos 1;i run s t London, 1S9:1) ; Chine mom, t tatting and Polishing of Precious Stones," it/. Mincrid induNtry, viii. (Nett' lark, Punt. For methods of distinguishing diamonds. consult Claremnt. Identification of lent.." Thi. Mini rid industry. Vol. Vii. (New' :•44. 11ENIs: CA11110N.