The gilding, however, has been more effectually preserved in the case of another cold process which came into vogue before the end of the seventeenth century, and rapidly spread from Bohemia, or perhaps rather from Silesia, to various parts of Germany. In the case of these zwischen gläser we are taken back to an old process, already known to the Alexandrian Greeks. The plan adopted in no way differs in principle from that made use of in the decoration of the beautiful bowls from Canosa, now in the British Museum (see p. [46]).[[204]] Very inferior to these in artistic merit are the little footless tumblers, with designs in gold, often hunting scenes, which seem to have been made on both sides of the Silesian-Bohemian frontier before the end of the seventeenth century. These are built up of two glasses, both somewhat tapering and both cut into an equal number of perpendicular sides, so that when the smaller of the two was inserted into the interior of the larger the glasses fitted exactly, and could not rotate one upon the other. The inner glass being somewhat the taller, we find the ring of junction, which is generally concealed by a band of gold, about half an inch or so below the top of the glass. The edges are so exactly bevelled that this line of junction is barely perceptible even to the touch. Before fitting the two glasses together, the inner one had been coated on the outside with gold-leaf, and the design carefully engraved on the gold with a steel point; while on the inside of the outer glass a coating of old linseed oil or of varnish had been smeared. I should add that a medallion of ruby glass, variously ornamented, is usually found at the bottom of these tumblers inserted between the two layers of glass, or sometimes replacing the base of the outer cylinder. These glasses will not stand warm liquids: an example in the British Museum is disfigured by some large flattened blisters, probably the result of heat.[[205]] Glasses built up in this manner may of course be decorated in other ways; the gold-leaf, for instance, may be replaced by silver foil. Kunckel, of ruby-glass fame, describes a method in which the inner glass is plainly gilt, while the outer one is painted on the inside in imitation of precious marbles (Ars Vitraria Experimentalis, 1679). I have seen examples of this manner of decoration in German museums.
CHAPTER XVII
THE GLASS OF GERMANY—continued
German Cut and Engraved Glass—The Ruby Glass of Kunckel—Milch Glass
I have still to describe the origin and development of a method of decorating the surface which forms, I may almost say, the last main division in the artistic history of glass. For when I come in subsequent chapters to treat of Dutch and English glass—and with this my task practically closes—it will be found that this glass falls almost entirely under the head, and is in a general way an outcome, of the engraved or cut glass of Germany.
Here at the beginning I am confronted with a difficulty of a class only too often met with when treating of the technique of the minor arts—the difficulty of finding in our language suitable words to express, without danger of misconception and confusion, the practical details of the matter in hand. I have now to deal with the methods by which the surface of glass may be cut, polished, scraped, or eaten away, so as to form an artistic design. This, I may say at once, can be effected by any one of the following methods:—
1. By scratching with a diamond. I can find no other word; the term ‘engraving’ is vague and ambiguous; to use the word ‘etching’ is still worse, for though the result resembles in a measure the etched line on copper, this expression should be reserved for the process by which the surface is eaten away (the German ätzen) by acid.
2. By removing the surface by means of a small revolving wheel, or more rarely, of a cutting-tool, with the aid of emery or other hard powdered stone. The term ‘engraving’ may well be used here, if it is understood in the sense in which we speak of an ‘engraved gem,’ for small hard stones have been cut in this way from ancient times.
3. When, however, by means of a large wheel, the surface is deeply cut away, we may better use the words ‘cutting’ or ‘carving.’ The grinding down of the surface and subsequent polishing, as in the case of glass cut into facets, would fall into this division. It is, however, often difficult to say which of these terms—engraving, cutting, or grinding—it is preferable to use; nor is the use of the German words ‘schleifen’ and ‘schneiden’ much more definite.
4. By exposing parts of the surface to the fumes of hydrofluoric acid, the only acid that will attack glass. This process may well be called etching.
We have already spoken of the use of the diamond by the Venetians for scratching lace-like designs upon the surface of their thin glass, so unsuitable for other forms of engraving. The diamond point was early used in a similar way in Germany. Mathesius, after speaking of the imitations of the vetro di trina, made in his day in Silesia, proceeds to say that it is also the practice to draw (reissen) ‘auf die schönen und glatten Venedischen gleser mit demand [diamond] allerley laubwerck und schöne züge.’