1902 Encyclopedia > Diamond > Ornamental Uses of Diamonds
Ornamental Uses of Diamonds
Diamonds are chiefly used and valued as ornamental stones, and for this purpose they are cut in various forms according to the original shape of the crystals.
It is probable that the Indians knew some method of doing this at an early period, and it is said there were diamond polisher in Nuremberg even in 1373. Berghem of Bruges has the credit of having first used, in 1456, their own powder for this purpose. He found that by rubbing two diamonds on each other their were polished and facets formed, and acting on this hint, he employed diamond powder and a polishing wheel.
His countrymen continued to follow out the art with great success, but some two centuries ago the English cutters were the more celebrated. The trade then reverted to Holland, but is again returning to Britain, where many of the finest stones are cut.
The method has undergone little change, and is still chiefly effected by the hand, partly by rubbing one stone on another, partly by a wheel and diamond powder. Where there are flaws or large pieces of value to be removed, they are occasionally cut by iron wired armed with the powder, or split by a blow of a hammer and chisel in the direction of the natural cleavage. The latter is, however, a dangerous process, as the diamond is very brittle, and many valuable gems have been thus destroyed.
When reduced to a proper form, the facets are polished on a lapidarys wheel. The process demands not only great skill but much time and labour. The period required to reduce a stone of 24 or 30 carats to a regular form extended formerly to at least seven or eight months of constant work, and in the case of the Pitt diamond two years were needed; but the time is now greatly shortened by the use of machinery driven by steam.
Jewellers have long cut diamonds in three forms -- the brilliant, the rose, and tables. The brilliant is most esteemed, as giving highest effect to the lustre, and implying less reduction of the stone. It is, as it were, a modification of the primary octahedron, the most common form of crystal, and is show in its first form in fig. 6 and 7, and with the full number of facets in figs. 8 and 9. Figs. 4 and 6 show the upper surfaces, with the table, or principal face, in the middle, surrounded by the bezil, or upper faces, lying between its edge and the girdle, or common base of the two pryramids. The lower facet corresponding to the table is named the collet, and the whole portion below the girdle the collet side. The portion removed to form the table (generally 5/18ths) and the collet (1/18th ) is shown in fig. 10. Brilliants are usually set open, both the upper or table side and the lower collet-side being exposed. The rose cut (upper view, fig. 11; lateral view, fig.12) is given to stones which have too little depth to be cut as brilliants; it has the whole upper curved surface covered with equilateral triangles. The table diamond, fig. 13 and 14. the least beautiful, is adopted for broad stones of trifling depth, showing a series of four-sided facets above and below the girdle Recently brilliants are cut in the star form (taille à étoile), with the table above only one-fourth the diameter, and thus with less loss of weight. There are also "mixed" or less regular forms used to suit the shape of the stone; and even splinters of diamond of 1/500 carat are facetted. In all the forms the girdle ought to be perfectly smooth, as a rough edge often appears through some of the facets as a flaw, and injures the brilliancy of the stone.
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