GEMS. This appellation is employed in two different senses : first, in denoting jewels or precious stones, which from rarity and beauty, have always been highly prized by mankind ; secondly, in characterizing stones, which, though not of the former description, are sculptured or engraved with various subjects, and more especially if executed by the ancients. But the name of gems is likewise applied, in a less appropriate signification, to artificial compositions designed to imitate the finer precious stones, either when polished in the natural state, or when they have passed through the hands of the engraver. In our article MINE nALocv, we shall have occasion to consider the subject of precious stones at some length, and w,e shall at present confine our attention to the subject of Engi avid Gems.
It is probable that no stone of sufficient hardness was excluded front receiving the engravings of the ancients ; hut it has been doubted whether they were acquainted with the means of cutting the diamond, of sculpturing the emerald and topaz. Much difference is experienced in working hard stones: the emerald is only to be conquered by uncommon patience, and a long time is requisite to pro duce a good engraving. The Eastern nations are unac quainted with the proper method of cutting and polishing the diamond ; and it is said that little more than a century has elapsed since the means of disposing its lustre to the greatest advantage in brilliants was discovered. The an cient Jews, in the days of Aaron, according to Scripture, could engrave on diamonds; and if the same art was un known to the Greeks or Romans, they were sufficiently ac quainted with the use of this stone in cutting other jewels. But if we consider the ingenuity of the Greeks and Ro mans, it is not unreasonable to conclude, that they fre quently engraved on precious stones. There are indeed few instances of the fact: thousands of their works must have perished many centuries ago, and many are still to be brought to light. Yet it is affirmed, that the art of polish ing the diamond, as it now appears, is not of anterior date to the yearl 456, and that engravings upon it belong exclusively to the moderns, having been attempted only about the suc ceeding century. In the year 1500, Ambrose Caradosso, an Italian, engraved the portrait of a father of the church on a diamond, which he sold to Pope Julius II. a great patron of the arts, for 55001, an immense sum at that pe riod. His example was followed by subsequent artists, and diamond dust was used in reducing this gem itself.
The substances most frequently sculptured by engra vers, both ancient and modern, are rock crystal of different colours, jasper, calcedony, carnelian, onyx, blood stone. Rock crystal, which is well known, is not considered of sufficient hardness, and the same has been observed of ma lachite, which is also sometimes used. Jasper is found in great variety, as well in appearance as quality, and in pieces of large dimensions ; none-but the finest and most compact is employed; and this occurs both in the colder and warmer climates. Carnelian and calcedony are so nearly allied, that their names are mutually interchanged, according to the tinge which either exhibits; but the latter, which is also called white cornelian by lapidaries, is to be distin guished by a greyish-white colour, bearing marks which resemble the scoopings of a knife on wood, and occasion ally exhibiting a sky-blue colour. The ancients are sup posed to have obtained the best species by the route of Carthage, from the mountains of the Nasomenes in Africa, and also from Thebes. One of their most favourite stones was the cornelian, on which all the ingenuity of their art has been anxiously bestowed: its colour, hardness, and tex ture, are the most favourable for delicate engravings, and it seems to have been diffused in much greater abundance than any other. This stone is seen of different shades, from cherry red to flesh colour, and sometimes of a yellowish tinge, or brownish colour; but exposed to moderate heat it becomes white. The ancients divided it into two spe cies, male and female, the latter being pale yellow; and they obtained both from India, Arabia, and other parts of Asia, as well as the Mediterranean islands. At present the finest cornelians come from the east, particularly the Indian peninsula, where they are found from the S•i.L. of a nut to several inches in diameter, and constitute a consi derable article of traffic : the Dutch also brought a quan tity from Japan, during the subsistence of their trade with that island. A large proportion of ancient and modern
engravings are executed on beautiful cornelian, the colour of which may be deepened and improved by the proper application of heat. The onyx has been esteemed valua ble since the earliest periods or Jewish history. from the singular combination of its colours ; and it was equally prized by the Greeks and Romans, \vim applied it to their most valuable works of art. This stone is considered a calccdony, the colours of which are disposed in alternate zones or strata. Generally they do not exceed two or three ; live or six are extremely rare. The proper gems of onyx consist of parallel zones, as these only can be worked to advantage ; but there are other two varieties with undulated zones, or concentric nuclei, resembling the eye of animals. Where the stripes are of various colours, lapidaries commonly call the stone a sardonyx, a vague and indefinite appellation, and used in another sense by mine ralogists. But some apply the name of sardonyx where the ground is coloured, and that of onyx where it is white. It is not known where the latter was obtained by the an cients, but it is now found principally in Germany and Scotland. Artists have ingeniously disposed of the com bination, particularly in sculpturing cameos or figures in relief : a white subject appears on a dark ground ; or if there be three colours, the third is artfully converted to drapery, or some accessory of the general design. This may be easily understood on reflecting, that the thickness of each zone is worked so as to leave one surface entire, or penetrating still deeper, the artist avails himself of two. M. Marlette speaks of a gem of this kind, consisting of four equidistant zones of different colours, describing four ellipses within each other in as great perfection as if drawn mathematically ; and in the centre was engraved a small figure of a Bacchante adapting his footsteps to the sound of his lyre, as if it had been a picture fitted into a frame. The largest onyx said to exist, is an oval of eleven inches by nine, on which is sculptured the apotheosis of Augus tus in four zones, two of which are brown and the others white. Several stones of the same species have attracted the particular notice of antiquarians : such is the Bruns wick vase, six inches in height, representing Ceres in quest of Proserpine; Venus on a marine animal, surrounded by Cupids, engraved upon an onyx of two zones ; Marcus Aurelius and Faustina in one of four zones, two white, and two of lilac. Many are wont to consider the finest works of art as insipid when not diversified by colour ; but this ob jection is removed by the onyx, and it has hence heen in great request both among the ancients and ourselves. Scipio Af ricanus, according to Pliny, first brought it into notice. Engraved gems of two colours, as the onyx, are called ca meos, a word of uncertain etymology. It is more usual ly applied to such subjects as are in relief or elevated, while all hollow engravings are called intaglios, a name adopted from the Italian, or in French en creux. Some artists are inclined to distinguish an onyx with a red ground as the cornelian onyx. The ancients seem to have been well acquainted with blood stone, called heliotrope by them, and on the continent at present, speckled agate. There are two species in use with engravers, one of which has the ground of deep green irregularly sprinkled with red specks, and not opaque. It is found in Siberia, Sicily-, Germany, and likewise in Scotland, in considerable pieces, but of very unequal quality ; and the red, which is thought to be iron, sometimes separates from the sub stance of the stone. Engravers have here, as in the for mer instance, availed themselves of colour ; and M. Brard acquaints us, that there is a gem, though not antique, in the national library at Paris, representing the head of Christ under flagellation, where the crimson specks imi tate the drops of blood. In the other species, the specks are so numerous, that at a little distance the whole stone appears of a reddish cast. Besides these the art of en graving has been exercised on many other stones, even on some which, from softness and the intermixture of colours, were ill adapted for it.