Although the art of engraving gems might have been preserved during the darker ages, it is doubtful whether the method of giving impressions to paste, without en graving, was not entirely lost. It was revived, however, by M. Hounberg, who, in the year 1712, explained it in such a manner, that all later artists have been enabled to follow his precepts. A quantity of soft, smooth, red tripoli is pounded in an iron mortar, sifted through a fine silk sieve, and set aside for use. Another species, called yellow, or Venetian tripoli, which has a natural kind of unctuosity, is then scraped with a knife, and bruised in a glass mortar, with a glass pestle, until reduced to a very fine powder ; the finer it is the more favourable for the impression. The red tripoli is now to be mixed to the like consistence of paste with water, and when moulded between the fingers, it is put into a small flattish crucible, scarcely exceeding half an inch in depth, and little more in bleadth at the surface than the size of the gem whose impression is to be taken. The crucible is then to be filled with the paste, slightly pressed down into it, and the dry yellow tripoli strewed over its surface. Here the stone which is to give the im pression must be laid, and pressed down so much on the paste, as to give it a strong, clean, and perfect impression ; and the tripoli is to be collected and applied nicely to the edges, with the fingers or an ivory knife. After the stone has lain a few seconds to allow the humidity -of the paste to moisten the dry powder of the yellow tripoli scattered over it, the operator must raise it carefully by a needle fixed in a wooden handle, and the crucible being inverted, it will fall out, while the impression remains on the tripoli still adhering to the crucible. The stone must now be ex amined, to ascertain that none of the paste has come off along with it, otherwise there will be a corresponding defect in the impression, and the operation must be repeat ed. Having allowed the crucible and paste to dry, the artist selects a fictitious gem of the suitable size to be laid over the mould, but in such a manner as not to touch the impression, which would thus be obliterated or injured ; and the crucible being gradually brought nearer the fur nace, is to be heated until it can no longer be touched by the hand, when it must be placed in the furnace under a muffle, surrounded with charcoal. When the gem begins to appear bright, it is the sign of being ready to receive the impression. The crucible must now be taken from the fire, and the hot gem pressed clown with an iron implement, to make it receive the impression from the mould below it ; after which the crucible is to be set by the side of the fur nace, to cool gradually without breaking. When cold, the gem may be removed, and its edges nipped or grated round with pincers, to prevent it from cracking, which sometimes happens. Red tripoli is used for the paste only from eco nomy, as it is the yellow species alone which is adapted for the purpose. Casts of plaster of Paris may be substituted for both, made into small cakes half an inch thick, and being put into a furnace without a crucible, the gem is to be pressed clown upon it to take the impression.
Many discussions have arisen among the learned concern ing the use of those ancient gems, now preserved with so much care in our cabinets. The beauty and rarity of na tural jewels constitute their principal recommendation, and they have always been employed as personal ornaments, some being more prized than others, according to fashion or ideal properties. It has been supposed that engraved
gems were applied in the same manner, and purposely sculptured for ornaments.
During some time, there was an ordonnance of the Ro man emperors, prohibiting the use of rings bearing their portraits, the infringement of which was little less than a capital crime ; and we are told of the praetor Paulus being exposed to imminent danger, from having a cameo repre senting the Emperor Tiberius. Vespasian wisely removed this restriction. But the use of those elegant subjects of mythology history, which appear in relief; is less evi dent, unless it had some relation to the religious principles of the owner, or was like a picture, designed to perpetuate historical events. It is said that the Romans long abstained from engraving any image of their gods on gems ; but adopting the religious fashions of other nations, they be came enslaved by superstitions. Augustus sealed with the head of Alexander, and then substituted his own, engraved by Dioscorides. Before resorting to either, he had sealed with a sphynx. Nero is said to have had a seal engraved with the subject of Apollo flaying Marsyas; that of Pom pey represented a lion holding a sword ; and the Emperor Galba retained the seal of his ancestors, representing a dog on the prow of a vessel. Sylla, proud of the capture of Jugurtha, caused a representation of the King Bacchus, delivering up the Prince, to be engraved on a ring which he wore on his finger, and always sealed with it ; and Sci pio Africanus did the same to commemorate one of his conquests.
The ancients entertained a great partiality for rings ; they wore many of the most valuable kinds at a time, load ing their fingers, in the words of Pliny, with extravagant wealth, censu opinzo digitos onerabant ; and these rings, as we have seen, contained either natural jewels or engraved gems. Most probably, numerous cameos were worn in the same way, merely for ornament, and cutting them might simply be a display of art in miniature, as sculpturing a statue, or painting a picture. But they had special collec tions of gems; as a taste for works of nature and art was not inferior at certain periods of ancient empires to what now prevails. Cxsar had a splendid cabinet, which he had collected at an immense expense, and of which the pearls of Great Britain constituted a valuable portion. This he consecrated to the temple of Venus Genetrix ; and Pom pey deposited the gems and rings found among the spoils of Mithridates in the capitol at Rome.
With the irruptions of barbarians, the arts were over thrown ; and the most ingenious works of antiquity were consigned to oblivion. Among those which escaped, some became votive offerings in the hands of the earar Chris tians to the shrines of their saints, and have thus been pre served through ages ; but by far the greater part were lost or destroyed.
See Pliny Historia Naturalis, lib. 37, 38. Gorlxus Dac tyliotheca. Gorious Dactyliotheca Smithinia. Gemnzarunz antiquarum, delectus ex przestantioribus desumptus qua. in Dactyliothecis Ducis Itlarlburiensis conservantur. Le Chau et Le Blond, Description des Principales Pierres Gravees du Cabinet de 1111e Due d'Orleans. Mariette. Traite des Pierres Gravees. Stosch, Gemince Antiquce czelatce sculp torum nominibus insignitx. Natter, Trait(' de la Methode Antique de Graver en Pierres fines. Raspe, Descriptive Catalogue of Tassie's Gems, 2 vols. in 4to. Memoires de l'Acadenzie Royale, 1712. Orschall, Sol sine veste. Fon tanieu. l'Art de faire les Cristaux, Paris, 1778, in 8ro ; and Journal de Physique. (c)