Enamelling on Glass
I now for the first time have to treat of the decoration of glass by enamel painting. It may be as well here to explain that in a true enamel, as the term is used in ceramic and vitreous art, the coloured decoration is applied to the glassy surface (either glaze or glass body) in the form of a pigment worked up with water or other liquid. Such enamel paints are composed, in later times at least, of a base of silicate of lead (the flux), coloured by various metallic oxides. It is essential that these enamels should be more fusible than the body on which they are painted, so that when subjected to the heat of the muffle-fire they may be completely fused, while the glass or glaze on which they rest is not more than superficially softened. Such enamel decoration, whether on porcelain or on glass, may vary from a mere wash of colour on the one hand, of which it is sometimes difficult to say whether it has ever been subjected to the heat of the muffle-fire, to a true vitreous covering on the other, where the various colours stand out in relief like so many jewels.
I may say at once that the Romans, as far as we know, never attained to any great success in this method of decoration. Its full development was reserved for the Saracens of the thirteenth and fourteenth centuries. This is indeed the one important advance made in the artistic manipulation of glass since ‘the palmy days of Rome.’
Not but that the Romans, and probably to some extent the Phœnicians and the Alexandrian Greeks before them, did not draw and paint upon their glass; but if we may judge from the rare and fragmentary examples that have survived, they were unable to obtain much decorative effect by this means; again, the very poverty and the paint-like quality of such enamels as they used, have doubtless in many cases led to their total disappearance from the surface of the glass.[[36]] The painting on the cup-like lids of the little bowls from Cyprus I have already mentioned. On a few fragments of thin glass from Egypt, draped figures have been painted in opaque colours. Perhaps the nearest approach to an effective use of enamel colours may be seen on two little cups found in graves of the fourth century at Varpelev, in Denmark. These Scandinavian tombs have yielded many interesting pieces of glass, as well as some bronze vessels—possibly booty brought home from marauding expeditions. The designs on these cups (they are illustrated in the Proceedings of the Copenhagen Antiquarian Society, 1861) are thus described by Mr. Nesbitt: ‘On the larger one are a lion and a bull, on the lesser two birds with grapes.... The colours are vitrified and slightly in relief—green, blue, and brown may be distinguished.’ (Slade Catalogue, p. xvi. See also some account of glass from these and other Scandinavian tombs in Montelius and Reinach, Les temps préhistoriques en Suède.)
But the most important and the best preserved example of enamelling on glass is to be found in a small bowl, probably of the third or fourth century, preserved in the treasury of St. Mark at Venice. To this important collection I shall have more than once to return.[[37]] The little bowl in question—something over three inches in height—is of a translucent glass of a winy or purplish colour. The seven larger medallions that surround the body are filled with mythological subjects in a fairly good classical style; the pale buff-coloured figures on a black ground imitate an onyx cameo. Each medallion is surrounded by a circle of rosettes of brilliant colours—blue, red, purple, and white. The angular spaces are filled by smaller medallions, each containing a head, and the remaining ground is occupied by a tracery of gold. According to the Canonico Passini, this decoration is in very slight relief, and is executed in what can scarcely be regarded as a true vitrified enamel. The bowl has been mounted at a later time in a light setting of silver gilt with elegant winged handles. But what is more curious, at some time previous to the addition of the mounting, a band of white ornament, resembling cufic letters, but apparently illegible, has been painted round the inside just below the rim, and again outside the base. Much of this later ornament has been abraded, although the original decoration is well preserved, and I think that this fact is an argument in favour of the earlier work being after all of the nature of a true enamel fixed by fire. I describe this bowl here as I cannot see any trace of Byzantine influence in the purely classical medallions.[[38]]
Finally, on a few of the gilt catacomb glasses, of which I shall speak shortly, a little coloured enamel is sparingly applied here and there, especially in the draperies.