LAPIDARY, ART OF. The art of the lapidary, or that of cutting, polishing, and engraving gains, was known to the ancients, many of whom have left admir able specimens of their skill. The Greeks were passionate lovers of rings and en graved stones ; and the most parsimo nious among the higher classes of the Cyrenians are said to have worn rings of the value of ten mince (about $150 of our money). By far the greatest part of the antique gems that have reached modern times, may be considered as so many models for forming the taste of the stu dent of the fine arts, and for inspiring his mind with correct ideas of what is truly beautiful. With the cutting of the diamond, however, the ancients were unacquainted, and hence they wore it in its natural state. Even in the middle ages, this art was still unknown ; for the four large diamonds which enrich the clasp of the imperial mantle of Charle magne, as now preserved in Paris, are uncut, octahedral crystals. But the art of working diamonds was probably known in Hindostan and China, in very remote periods. After Louis de Berghen's dis covery', in 1476, of polishing two dia monds by their mutual attrition, all the finest diamonds were sent to Holland to be cut and polished by the Dutch artists, who long retained a superiority, now no longer admitted by thelapidaries of Lon don and Paris.
The operation of gem-cutting is abridg ed by two methods : 1st, by cleavage ; 2d, by cutting off slices with a fine wire, coated with diamond powder, and fixed in the stock of a hand-saw. Diamond is the only precious stone which is out and polished with diamond powder, soaked with olive oil, upon a mill plate of very soft steel.
Oriental rubies, sapphires, and to pazes, are cut with diamond powder soaked with olive oil, on a copper wheel. The facets thus formed are afterwards polished on another copper wheel with tripoli, tempered with water.
Emeralds, hyacinths, amethysts, gar nets, agates, and other softer stones, are cut at a lead wheel, with emery and water ; and are polished on a tin wheel with tripoli and water, or, still better, on a zinc wheel, with putty of tin and water.
The snore tender precious stones, and even the pastes, are cut on a mill-wheel of hard wood, with emery and water ; and are polished with tripoli and water on another wheel of hard wood.
Since the lapidary employs always the same tools, whatever be the stone which he cuts or polishes, and since the wheel discs alone vary, as also the substance he uses with them, we shall describe, very briefly, his apparatus, and the manipu lations for diamond-cutting, which are applicable to every species of stone. Diamonds are cut at the present day in only two modes ; into a rose dia mond, and a brilliant. We shall there fore confine our attention to these tfiro forms.
The rose diamond is flat beneath, like all weak stones, while the upper face rises into a dome, and is cut into facets. Most usually six facets are put on the central region, which are in the form of triangles, and unite at their summits ; their bases abut upon another range of triangles, which being set in an inverse position to the preceding, present their bases to them, while their summits ter minate at the sharp margin of the stone. The latter triangles leave spaces between them which are likewise cut each into two facets. By this distribution the rose diamond is cut into 24 facets ; the sur face of the diamond being divided into two portions, of which the upper is called the crown, and that forming the contour, beneath the former, is called dentelle (lace) by the French artists.
According to Mr. Jeffries, in his Trea tise on Diamond; the regular rose dia mond is formed by inscribing a regular octagon in the centre of the table side Of the stone, and bordering it by eight right-angled triangles, the bases of which correspond with the sides of the octagon ; beyond these is a chain of eight trape ziums, and another of sixteen triangles. The collet side also consists of a minute central octagon, from every angle of which proceeds a ray to the edge of the girdle, forming the whole surface into eight trapeziums, each of which is again subdivided by a salient angle (whose apex touches the girdle) into one irregular pentagon and two triangles.