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).
(A. S. M.; A. H. Sm.)
[1] For Nos. 1-4 see Furtwängler, pl. 14; for Nos. 2-4 see Evans, Rev. archéologique, xxxii. (1898) pl. 8.
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.