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Rh at first sight is attractive as refined and delicate is after all an exaggerated minuteness of execution, entirely devoid of the ancient spirit. The success with which modern engravers imposed on collectors is recorded in many instances, of which one may be taken as an instructive

type. In the Bibliothèque Nationale is a gem (Chabouillet’s catalogue, No. 2337), familiarly known as the signet of Michelangelo, the subject being a Bacchanalian scene. So much did he admire it, the story says, that he copied from it one of the groups in his paintings in the Sistine chapel. The gem, however, is evidently in this part of it a mere copy from Michelangelo’s group, and therefore a subsequent production, probably by da Pescia. In our own day the engraving of cameos has practically ceased to be pursued as an art. Roman manufacturers cut stones in large quantities to be used as shirt-studs and for setting in finger-rings; and in Rome and Paris an extensive trade is carried on in the cutting of shell cameos, which are largely imported into England and mounted as brooches by Birmingham jewelry manufacturers. The principal shell used is the large bull’s-mouth shell (Cassis rufa), found in East Indian seas, which has a sard-like underlayer. The black helmet (Cassis tuberosa) of the West Indian seas, the horned helmet (C. cornuta) of Madagascar, and the pinky queen’s conch (Strombus gigas) of the West Indies are also employed. The famous potter Josiah Wedgwood introduced a method of making imitations of cameos in pottery by producing white figures on a coloured ground, this constituting the peculiarity of what is now known as Wedgwood ware.

Gem Collectors.—The habit of gem-collecting is recorded first in the instance of Ismenias, a musician of Cyprus, who appears to have lived in the 4th century But though individual collectors are not again mentioned till the time of Mithradates, whose cabinet was carried off to Rome by Pompey, still it is to be inferred that they existed, if not pretty generally, yet in such places as Cyrene, where the passion for gems was so great that the thriftiest person owned one worth 10 minas, and where, according to Aelian (Var. hist. xii. 30), the skill in engraving was astonishing. The first cabinet (dactyliotheca) in Rome was that of Scaurus, a stepson of Sulla. Caesar is said to have formed six cabinets for public exhibition, and from the time of Augustus all men of refinement were supposed to be judges both of the art and of the quality of the stones.

In the middle ages the chief collections were incorporated in works of art in the church treasuries. The first collector of modern times was, as already mentioned, Pope Paul II., who was followed by a long succession of princely and noble collectors such as Lorenzo de’ Medici and the great earl of Arundel. The collection of the latter passed into the hands of the dukes of Marlborough and thence into the possession of Mr David Bromilow. The collection was finally dispersed by auction in June 1899.

In modern times the principal collections are contained in state museums. The cabinets of Vienna and of the Bibliothèque Nationale are incomparably rich in the historic cameos. Those of the British Museum and of Berlin are the strongest in their range over the whole field of the gem-engraver’s art.

.—For the fullest general account of the subject (with especial attention to the gems of classical antiquity) see A. Furtwängler, Die antiken Gemmen, Geschichte der Steinschneiderkunst im klassischen Altertum, in 3 vols (1900). See also E. Babelon, La Gravure en pierres fines, camées et intailles (1894); A. H. Smith, “Gemma” and “Sculptura,” in the 3rd edition of Smith’s ''Dict. of'' Antiquities; J. H. Middleton, The Engraved Gems of Classical Times (1891). Much curious information is in the works of C. W. King: Handbook of Engraved Gems (1866); Antique Gems (1866); The Natural History, Ancient and Modern, of Precious Stones and Gems, and of the Precious Metals (1865); Antique Gems and Rings (2 vols., 1872).

Special Periods:—Babylonia, &c.—Menant, “Les Pierres gravées de la haute Asie,” Recherches sur la glyptique orientale (1883–1886).

Egypt.—For the early cylinder sealings, &c. see Petrie, “Royal Tombs of the First Dynasty” (Egypt Explor. Fund, XVIIIth Memoir), p. 24; pls. 12, figs. 3 to 7, and pls. 18-29; Amélineau, “Nouvelles Fouilles d’Abydos, 1897–1898,” Compte rendu, pp. 78, 423; pl. 25, figs. 1-3.

The Bible.—Petrie, “Stones (Precious),” in Hastings’ ''Dict. of the'' Bible.

Phoenician.—See M.A. Levy, Siegel und Gemmen, with three plates of gems having Phoenician, Aramaic, old Hebrew and other inscriptions (Breslau, 1869); and, on the same subject, De Voguë, in the Revue archéologique, 2nd series (1868), xvii. p. 432, pls. 14-16.

Crete.—Articles by A. J. Evans in Journal of Hellenic Studies, xiv., xvii., xxi., and in Annual of British School at Athens, vi. and onwards.

Classical Gems.—See Furtwängler, op. cit.

Gnostic Gems.—Cabrol, ''Dict. d’archéologie chrétienne'', s.v. “Abrasax.”

For the controversy as to gems with artists’ signatures, see Koehler, Abhandlung über die geschnittenen Steine, mit den Namen der Künstler; Koehler’s collected works, ed. Stephani, vol. iii. (1851); Stephani, Notes to Koehler as above; also Über einige angebliche Steinschneider des Alterthums (St Petersburg, 1851); Brunn, Geschichte der griechischen Künstler, ii. (1859), pp. 442–637; Furtwängler, ''Jahrbuch d. k. deutsch. arch. Inst.'' iii. (1888), pp. 105, 193, 297; iv. (1889), p. 46, and Geschichte, passim.

For the history of the Poniatowski gems, see Reinach, Pierres gravées, p. 151.

Catalogues.—The chief catalogues dealing with modern public collections are: Berlin, A. Furtwängler, Beschreibung der geschnittenen Steine im Antiquarium (1896); British Museum, A. H. Smith, A Catalogue of Engraved Gems in the British Museum (Dept. of Greek and Roman Antiquities) (1888); Paris, Bibliothèque Nationale, Chabouillet, ''Catalogue ... des camées et pierres gravées'' de la Bibliothèque Impériale (1858); E. Babelon, Catalogue des camées ... de la Bibliothèque Nationale (1897).

Modern Engraving.—Vasari vii. p. 113 (ed. Siena, 1792); continued by Mariette, Traité des pierres gravées (1750), i. p. 105. The older books on gems are very numerous, but those of present-day importance are not many. Faber, ''Illustrium imagines ... apud'' Fulvium Ursinum (Antwerp, 1606); Stosch, Gemmae antiquae caelatae, scalptorum nominibus insignitae (Amsterdam, 1724); Winckelmann, Description des pierres gravées du feu Baron de Stosch (1760); Krause, Pyrgoteles, oder die edlen Steine der Alten (1856); a convenient reissue of Stosch, and seven others of the older works, by S. Reinach, ''Pierres gravées, &c. ... réunies et rééditées, avec'' un texte nouveau (1895).

Pastes.—The principal collection of glass and sulphur pastes from gems was that issued by James Tassie of Glasgow, with A Descriptive ''Catalogue of a General Collection of ... Engraved Gems ... arranged'' and described by R.E. Raspe (the author of Baron Munchausen) (1791).

GEM, ARTIFICIAL. The term “Artificial Gems” does not mean imitations of real gems, but the actual formation by artificial means of the real precious stone, so that the product is identical, chemically, physically and optically, with the one found in nature. For instance, in chemical composition the lustrous diamond is nothing but crystallized carbon. Could we take black amorphous carbon in the form of charcoal or lampblack and dissolve it in a liquid, and by the slow evaporation of that liquid allow the dissolved carbon to separate out, it would probably crystallize in the transparent form of diamond. This would be a true synthesis of diamond, and the product would be just as much entitled to the name as the choicest products of Kimberley or Golconda. But this is a very different thing from the imitation diamond so common in shop windows. Here the chemist has only succeeded in making a paste or glass having limpidity and a somewhat high refractivity, but wanting the hardness and “fire” of the real stone.

The Diamond.—Within recent years chemists have actually succeeded in making the real diamond by artificial means, and although the largest yet made is not more than one-fiftieth of an inch across, the process itself and the train of reasoning leading up to such an achievement are sufficiently interesting to warrant a somewhat full description. Attempts to make diamonds artificially have been numerous, but, with the sole exception of those of Henri Moissan, all have resulted in failure. The nearest approach to success was attained by J. B. Hannay in 1880 and R. S. Marsden in 1881; but their results have not been verified by others who have tried to repeat them, and the probability is that what was then thought to be diamond was in reality carborundum or carbide of silicon. 