Page:The American Cyclopædia (1879) Volume VII.djvu/676

 664 GEM for his copies of ancient gems and exact imita- tions of the ancient letters. The Costanzis and many others also attained great repute ; and in the present century are some whose productions, as those particularly of Signor Rega of Naples, rank with the famous, antique gems. Among the Germans, Daniel Engelhard of Nuremberg, a friend of Albert Diirer, was celebrated for his skill in engraving crests and arms. He died in 1552. The works of the Pichlers, father and son, who came from Tyrol, are of the high- est merit, especially those of the father. The son was much in Italy, and is often spoken of as an Italian. The celebrated Poniatowski col- lection of antique gems has recently been cred- ited to the elder Pichler. Natter of Swabia, who died in 1763, was not only a workman of the most delicate skill and refined taste, but a student and author also, and published in 1754 a treatise specially devoted to his art : Traite de la metkode antique de graver en pierres fines comparee avec la methode moderne. From this work it appears that the ancients employed the same sort of tools and the same methods as those in use at the present day. The modern practice is described by Holtzapffel in vol. iii. of his "Mechanical Manipulation." The ap- paratus employed in engraving consists of a foot lathe attached to a small table, upon which is fixed a little pillar for holding the horizontal pulley, which is the receptacle for the cutting tool. This part of the apparatus is called the mill. The tools are soft iron wire' spindles care- fully annealed and nicely fitted to the hollow axis of the pulley. Only one is used at a time. When set in its place it projects through the bearings of the pulley, one end extending hori- zontally on the right-hand side of the operator, who sits at his work in front of the table. This extremity of each tool is fashioned for its spe- cial work. Most of them terminate in a small disk, the edge of which, as it rotates rapidly, cuts lines in the stone held up against it, the tool being fed with diamond dust and oil. The larger sized disks are only about a quarter of an inch in diameter, and from this they are made of decreasing sizes down to -^ of an inch, when the disk can scarcely be distinguished by the eye from the stem. They are also variously shaped for special kinds of cutting. The stone intended to be engraved is usually shaped by the lapidary, and is sometimes set by the jew- eller before it is engraved. If not set, the en- graver secures it to a wooden handle by the cement known as the lapidary's ; or if set, he secures it in a notch in a piece of cork. The polish is removed by roughening the face with a suitable cutting powder, as the tools work better upon a rough surface, and the outline of the design, which is next marked with a brass point, is the more conspicuous. The area thus enclosed is then sunk by the tools to a suitable depth ; and within this the details of the design are successively introduced and ex- cavated. For the parallel lines, called color lines, a thicker disk with two cutting edges is employed, its form being that of a little pulley ; the two edges are just as far apart as the lines they are intended to cut, and as one pair is cut the stone is moved so as to bring the outer edge of the disk into the groove marked by the other edge, and thus the work goes on step by step over the surface to be thus " colored." The plan must be perfectly understood by the art- ist at the commencement of his work, and as it goes on he watches the effect produced with the aid of a magnifying glass conveniently at- tached to a stand over the tool, and occasionally takes a proof of his work in wax. After the stone is engraved the polish is restored to the flat surface by a pewter polishing disk or lap fed with rotten stone and water. The engraved portions are polished with great care, first by using in the mill copper tools charged with diamond powder ; this buries itself more deeply in the copper than in the iron tools, and a smoother surface is thus obtained. Boxwood tools charged with still finer diamond powder are next used, and after these copper tools charged with rotten stone and water. The harder gems, excepting the diamond, which is engraved with the greatest difficulty, are better adapted for this process than those of softer quality. The latter are liable to hold the dia- mond powder and cause it to wear out the tools ; they do not when finished present such smooth and highly polished surfaces as the harder stones. The amethyst is considered as soft a stone as can be cut very smoothly. Car- nelian and bloodstone are of close texture, and admit of excellent work ; the ruby cuts slowly, I but small pieces are apt to flake off. The sap- i phire is firm and close ; it cuts slowly, but pre- ! sents beautifully smooth surfaces. ARTIFICIAL GEMS. The great value attached to precious stones led at an early period to successful at- tempts to imitate them. The Egyptians pos- sessed the art of coloring glass, and among their mixtures they produced excellent imitations of the most beautiful gems, so that, as Pliny states, it was difficult to distinguish the false from the real. Their artificial emeralds, sapphires, and hyacinths are spoken of by various ancient au- thors. Some of the first named were of such gigantic size that they were used in the con- struction of statues, as of that of Serapis in the Egyptian labyrinth, 13 ft. in height. Another presented by the king of Babylon to an Egyp- tian Pharaoh was 6 ft. long and 4J- broad ; and an obelisk in the temple of Jupiter 60 ft. high and 6 ft. broad was composed of four artificial emeralds. These were very extraordinary pro- ductions if made only of pieces of colored glass. Seneca also makes mention of one in his time who manufactured artificial emeralds. Beck- mann states that in some ancient collections at Rome are piece's of colored glass, which were once used as jewels, "in the Museum Yictorium are seen a chrysolite and emerald of faultless execution. In the 17th century the discovery of the preparation of gold and bin- oxide of tin, called purple of Cassius, afforded