In the time of Augustus, the Roman architects made use of glass in their mosaic decorations ; and several spe cimens of this glass have been found among the ruins of the villa of the emperor Tiberius, in the island of Capri. Some of these specimens have been examined and analy sed by Klaproth. They consist of pieces of red, green, and blue glass.
The first of these is of a lively copper red colour, per fectly opaque, and very bright at the place of recent fracture. The green grass has a light verdigris colour, is opaque, and has a scoriaceous shining fracture. Two hundred grains consisted of The blue glass had a sapphire colour, verging towards that of smelt, and was transparent at the edges only. Some of the plates of it are not coloured throughout the whole of their mass, but only through about two thirds of their thickness. Each of the strata is so distinct, as to give the ;Appearance of a blue and a colourless plate adhering at their broad surfaces.
A still more singular art of forming pictures with co loured glass was known and practised by the ancients. It consists of variously coloured glass fibres, fitted with the utmost exactness, so that a section across the fibres re presents the object to be painted. These fibres, when pro perly joined together, are afterwards cemented by fusion into a homogeneous and solid mass. Specimens of this art seem to have been first discovered about the middle of the last century. Count Caylus first describes them in his Collection of Antiquities, and Winkelman in his Annotations on the history of the Art among the Ancients, under the name of pictures made of glass tubes. Sulzer, in his Theory of the Polite Arts,, describes, in the article Mo saic, specimens which he had seen at Dresden ; and Kla proth has given drawings of one which he has in his own possession. The following description of two pieces of this kind of glass, which were brought to Rome in 1765, is given by Winkelman: Each of them is not quite 1 inch long, ands of an inch broad. One plate exhibits, on a dark ground of variegated colours, a bird representing a duck of various very lively colours, more suitable to the Chinese arbitrary taste, than adapted to show the true tints of nature. '['he outines are well decided and sharp, the colours beautiful and pule, and have a very striking and brilliant effect ; because the artist, according to the nature of the parts, has in some employed an opaque, and in others a transparent glass. The most delicate pencil of the miniature painter could not have traced more accurately and distinctly, either the circle of the pupil of the eye, or the apparently scaly fea thers on the breast and wings, behind the beginning of which this piece had been broken. But the admiration of the beholder is at the highest pitch, when, by turning the glass, he sees the same bird on the reverse, without per ceiving any difference in the smallest points ; whence we could not but conclude, that this picture is continued through the whole thickness of the specimen ; and that, if the glass were cut transversely, the same picture of the duck would be found repeated in the several slabs; a con clusion which was still farther confirmed by the transpa rent places of some beautiful colours upon the eye and breast that were observed. The painting has on both
sides a granular appearance, and seems to have been form ed, in the manner of mosaic works, of single pieces ; but so accurately united, that a powerful magnifying-glass was unable to discover any junctures. This circumstance, and the continuation of the picture throughout the whole substance, rendered it extremely difficult to form any di rect notion of the process or manner of performing such a work. And the conception of it might have long con tinued enigmatical, were it not that, on the section of the fracture mentioned, lines are observable, of the same co lours which appear on the upper surface, that pervade the whole mass from one side to the other; whence it became a rational conclusion, that this kind of painting must have been executed by joining variously coloured filaments of glass, and subsequently fusing the same into one coherent body. The other specimen is about the same size, and made in the same manner. It exhibits ornamental draw ings of green, white, and yellow colours, which are traced on a blue ground, and represent volutes, beads, and flow ers, resting on pyramidally converging lines. All these are very distinct and separate, but so extremely small, that even a keen eye finds it difficult to pursue the subtile end ings, those in particular in which the volutes terminate. Notwithstanding which, these ornaments pass uninterrupt edly through the whole thickness of the piece." One of the two specimens which we have mentioned as in the possession of M. Klaproth, is represented in Plate CCLXXV. Fig. 4. Both the pieces have a heart-shaped form, their principal front being flat, and the reverse con vex. The length of one of them is one inch, its breadth four-fifths, and its thickness, two-fifths. The other spe cimen is two-thirds of the size of the first ; but they are both nearly alike in the colouring and manner of drawing. The principal mass of the large specimen is a dark and perfectly opaque, but the smaller one, which is in some places transparent, has a sapphire blue colour. The blue ground is ornamented with voluted stellular, minute flow ers, on such a small scale as to be scarcely imitable by the miniature painter. Their colours are red, green, brown, sky-blue, and white, and are all pure and lively. The de lineations pervade the whole mass; and it is obvious from examining a fracture, that those minute ornaments are formed of parallel glassy fibres of various hues, aggluti nated by fusion.