Onyx they are not uncommon; and a good engraving on a fine Oriental Onyx will command a higher price than upon any other gem. And there is good reason for this preference, since the design penetrating through the surface into the next layer is brought out in full relief by the contrast of colour, and thus is conspicuous at a distance, which is not the case with a transparent stone, for it must be held up to the light to show the engraving.

The use of the Sardonyx was first made fashionable in Rome by Scipio Africanus the elder: the favourite gems of the Emperor Claudius were the Sardonyx and the Emerald.

We may return to the subject of the precious Onyx to observe that, although the true Oriental kind still retains its value, pieces of large dimensions bringing the high price above mentioned, yet the great majority of the stones so called at present by jewellers are almost worthless. These generally present strong contrasts of red and white, or black and white layers. These colours are produced artificially by boiling the stone, a kind of flint, for several days in honey and water, and then soaking it in sulphuric acid to bring out the black and white, and in nitric to give the red and white layers. They all come from Germany, where the secret was either discovered a few years ago, or, as some assert, introduced from Italy. Pliny says that all gems are brightened by boiling them in honey, especially in Corsican (noted for its acridity), although they are injured by all other acids. I have myself seen an antique Agate, which had been reduced by fire to nearly the appearance of chalk, restored to almost its original colour by being treated in this manner for three consecutive days and nights. The antique gems, indeed, particularly the Sards and the several varieties of the Onyx, are incomparably superior to anything of the kind which we meet with in Nature at the present day; but it would be

hazardous to ascribe this excellence to any artificial treatment of the stones by the old lapidaries, as it may have been the consequence of their better and more abundant supply of the material from sources now closed to us. This we know was the case with many antique marbles, such as the Rosso and Giallo Antico, the Verde and the Cipollino, all only known at present as existing in fragments of ancient architecture. Numidia is said to have furnished the Giallo; Laconia the Verde; Carystus the Cipollino; but the coast of the Red Sea was the chief source both of the coloured marbles of antiquity and also of many of their most valuable gems.

The enormous dimensions of the pieces of Sardonyx used by the ancient engravers for some of their more important works, as the Onyx of the Sainte-Chapelle, have induced many to believe that they were a production of art. Veltheim goes so far as to say that they were made by fusing obsidian and sulphur together; but this experiment, when tried, gave nothing but a black porous glass. De Boot gives a ridiculous. receipt for making the Sardonyx by steeping pounded shells in lemon-juice for several days, and with the white cement thus made forming the upper layer upon a Sard or Carnelian. It is curious, however, to notice that the same idea as to the artificial origin of the Sardonyx appears to have prevailed in the days of Theophrastus; at least, this seems the most natural interpretation of his words (On Stones,' chap. 61): "Earthy minerals, these assume all kinds of colours, by reason of the diversity of the subjects and of the influences acting upon them; of which, some they soften (by fire), others they fuse and pound, and so put together those stones that are brought from Asia." Now we must remember that the Murrhina, and the Gemma of which the huge draught-board (carried in Pompey's triumph) was made, were not known at Rome before the conquest of Asia, long after the age of Theophrastus.

PLASMA.

This word, sometimes written Prasma, whence the French name of the stone, Prisme d'Emeraude, is merely the Italian corruption of Prasina Gemma, according to their common vulgarism of interchanging R with L, and vice versa. Thus the Tuscan peasant always says Leopordo for Leopoldo. This gem is merely Calcedony coloured green by some metallic oxide, probably copper or nickel, and is, in fact, a semi-transparent green Jasper; and although it often approximates to the finest Emerald in colour, yet it is never pure, but always interspersed with black spots, or with patches of the dull yellow of the original species, blemishes aptly named by Pliny "sal et pterygmata," grains of salt and bees' wings. But of a pale-green variety pieces do occur quite free from flaws and spots; such, however, are probably rather to be considered as varieties of the Chryoprase. These last are the true Prases of the ancients, so called from their exact resemblance to the colour of the leek, and some of the best stones of this variety will be found quite equal to the Emerald in tint, though devoid of its lustre. I have also met with the Grammatias of Pliny-"the Prase with a white line running through it"-employed as a Gnostic amulet; and also the kind "horrent with spots of blood;" specimens accurately determining the species of gem intended under his designation of Prase. The commonness of the stone when he wrote is clearly shown by his expression "Vilioris est turbæ Prasius," the Prase belongs to the vulgar herd.

The Plasma was a great favourite with the Romans of the Lower Empire, but not of an earlier date, to judge from the circumstance that, although intagli on it are more abundant than on any other stone except the Sard and Carnelian, yet

I have never met with any of fine work, and antique, in this material. The subjects also of the intagli occurring in it are usually those chiefly in vogue at a late epoch of Rome, such as the Eagle, Victory, Mercury, Venus, and the Graces. I should conclude from this that the stone was a late importation into the Roman world, else it would certainly have been employed by good artists, both on account of its agreeable colour and of its resemblance to Calcedony in the facility of working. I have often met with camei in this stone, but all apparently of the Renaissance period. Its native country is now unknown, but large masses of it are occasionally discovered among the debris of ancient buildings in Rome. Several of the green gems distinguished by Pliny by the names of Tanos, Prasius, and Molochites, are now, to all appearance, included under the appellation of Plasma by collectors. Certainly the great variety of the tints and qualities of the stones now called Plasmas indiscriminately would have induced the ancients, whose mineralogical system was entirely based on external peculiarities, to class them under different species. The Molochites (now confounded with the Malachite or carbonate of copper) was quite a different substance, resembling the Emerald, although not transparent, good for making impressions on wax, and worn around children's necks as an amulet. It perhaps was the clear green Jade in which small figures for suspension are so often found. Prismatical beads" of Plasma, as well as of Garnet, are often found in the earth about Rome. They all range nearly about the same size, so that collectors have but little difficulty in forming an even row out of many distinct purchases. Here it may be added that our Malachite was the Chrysocolla

7 This tends to prove that one species amongst our Plasmas was the green Jasper of the ancients, who often mention necklaces of

Jasper beads, as we shall see in the verses quoted from Naumachius.Vide Sapphire.

of the Romans, a name also given to native verdigris, from its use as a solder for gold work. Nero, as patron of the Green Faction, in one of his fits of extravagance caused the Circus to be strewn with the powder of this valuable ore, instead of the ordinary sand. Antique camei in Malachite, though extremely rare compared with the frequency of modern works in this material, nevertheless do exist. Amongst the Pulsky gems is a most lovely bust of a Bacchante, of the best period of Roman art, still retaining in portions the thin hard patina of brown oxide, with which its surface was entirely encrusted when it came into the hands of the present owner-a convincing proof of the ages that must have elapsed since its concealment in the earth.

Diomede and Ulysses carrying off the Falladium: Greco-Italian. Agate.

JASPERS.

τὰς βοῦς και τὸν ἴασπιν ἰδὼν περὶ χειρὶ δοκήσεις

τὰς μεν ἀναπνειεῖν τονδὲ χλοηκομέειν.

Anthol. ix. 750.

"You'll deem this jasper, deftly graved with cows,

A

grassy mead where breathing cattle browse."

Of this stone the green semi-transparent kind was considered the most valuable by the Romans, and to this sort

8 This was the " Jasper " properly so called in the lapidary's language of the times: "Viret et sæpe trans

lucet Jaspis." Pliny goes on to notice its former high estimation and subsequent neglect.