CAM EO, is the name given to stones of different co lours, which contain sculptures in alto or basso relies o. The effect of nature is here combined with art, and the moderns have in vain attempted to imitate these relics of antiquity.
The onyx is a hard semipellucid stone, formed of se veral zones or strata of different colours closely united, and throughout blended together. As the colours are more distinct and opposite, the greater value is put upon the stone. Sonic species exhibit three colours, and in others only two arc seen, of which the upper is of a beau tiful white, on a ground of deep gray.
These two species of stone were selected by the an cients for engravings or sculptures in alto and basso re hero, as the colours would admit, or according to the choice of the artist, and the subjects represented were some of the most noted incidents in antiquity, such as the labours of Hercules, the rape of Proserpine, or the annunciation to Achilles of the death of Patroclus. But one chit: excellence consists in the ground being abso burly opposite and distinct from the colour of the sub ject. Thus, a white figure appears hi high relief, though the ground be of a deep shade, or even black ; and the judicious arrangement of the parts, where uniformity of colour is required, most eminently displays the skill of the artist.
Genuine cameos always bear a high value, propor tioned to the beauty of the execution and the quality of the stone. They are discovered in various coun tries, both in the natural state, and preserved from former times. Of late years, some very exquisitely finished have been recovered by Europeans who visited Delhi.
Though the moderns have been unsuccessful in sculpturing cameos, they have produced beautiful spe cimens of analogous workmanship in shells. Therr. the interesting events of ancient hiAory arc in like man ner chosen, and the relief is pure white, while the ground is blue. This invention is said to be of Sicilian origin. • .Another method of imitating the cameos of the an cients has been practised with very great success. Pieces of coloured glass are put into a crucible, alter nating with layers of chalk or Spanish white. The crucinle is
then placed on a fire, the heat of which increases gra dually for three bouts, till it becomes very i uoise. The pieces of glass then turn opaque without the ori ginal colour, and those pieces which h. no col• at all will become milk white like porcelain. if tl e heat has been well ttgulated, and not raised these opaque pieces of coloured glass may be soldered to one another, so as to imitate the difTerently coloured layers of the onyx. The coloured glass which is found in an cient church,s, a •c.• solor,imes only penetrated by the colour thrcug• half th...r thickness ; so that when pieces of it are rc,nocii_d opaque by the preceding process, the transparent part of it that was not pc nitrated b. the colour becomes white, and two differently co:oured layers _re thus obtained, without the process of sol dering. The white part of the glass is then ground down to the requisite thickness. and the figures are cut upon it either in alto or basso relievo by the common process.
If the subject to be engraved is only a simple head, it may be first cut out, and then fixed upon a piece of glass of a different colour. The head is first attached with gum to the piece of glass, and after the adhesion is sufli cicntly firm, the surface of the glass containing the head is laid upon a bed of tripoli, and pressed upon it as if a good impression of the head were required. The glass and the head are allowed to rest upon the tripoli till it is quite dry, and as soon as this happens, the whole is put into a furnace and exposed to an intense heat. The gum is then burnt off, and the head is soldered to the piece of coloured glass upon which it was placed. The hair of the figure may be afterwards coloured, by using a little, of the solution of silver in the spirit of nitre, and again exposing the head to a proper heat. For further infor mation on this subject, see Essais eur L'. Irt des anciens, de joindrc par lc fusion deu.r cspecce de verrr, pour le gra vure en relief, par 'Al. Gerhardt, Conseiller Priv& des Fi nances au department des mines du Roi de Prusse. (•v)