Thanks in a measure to the energy of Winter and to the support given to him, the little town of Warmbrunn soon became known all through Germany as well for its cut glass as for the warm springs to which it owed its name. As in other parts of Silesia, the glass industry, after the separation from Bohemia, suffered from the fiscal regulations of the new Prussian régime. Frederick the Great took an interest in the manufacture of glass, but this was shown rather in the encouragement and patronage accorded to the new glass-works that had been established nearer to his capital.
On the other side of the mountains also, at the end of the seventeenth century, some of the great Bohemian landholders were active in promoting the manufacture of glass on their estates. Of the Kinsky family and the town of Steinschönau (even to-day a great centre of the glass industry), we hear something in the curious account of his life left by a wandering glass-cutter, one Kreybich, who was born in that town in 1662. Kreybich, who had mastered the arts both of enamelling and engraving glass, carried his wares on his barrow all over Southern Germany. In his later journeys he pushed forward as far as Poland and Russia. As early as 1688 he is found in London, where, in spite of the competition of many new glass-furnaces (these, he confesses, turned out better metal than that which he had with him), he found a good demand for his engraved glass. When the wandering retailers of glass—we can hardly call them hawkers—returned to renew their supplies, then, says Kreybich, there was an eager demand from the glass-houses, and no less from the glass-cutters, the kugler, and the polishers. But not a few of these wandering glassmen carried, it would seem, their engraving-wheel and their tools with them, and engraved on the spot the arms or the initials of the purchasers of their glasses.
We may indeed regard the first half of the eighteenth century as the most flourishing period of the glass industry in Bohemia and Silesia. At the end of that time the Bohemian town of Haida—at the present day the centre of more than one branch of the glass manufacture—rose to importance, thanks to the fostering care of Count Kinsky. But the industrial and commercial element now came more and more to prevail. Enterprising manufacturers like Franz Weidlich of Steinschönau exported to Spain and Portugal, and others supplied the Eastern market as far as the Indies with glass summarily decorated with ‘little wreaths cut with a small copper wheel with the aid of emery.’ This Eastern trade passed through Vienna, and meeting with every encouragement from Maria Theresa and from Joseph II., soon undermined the time-honoured monopoly of the Venetians in the Levant and in Persia. With the Western market it was otherwise. The German glass had to reach the Peninsula by way of the Flemish ports, Antwerp and Ostend. What we have known as the Spanish Netherlands were now in Austrian hands, and the new government was eager to promote the local industries. The energetic firm of the Bonhommes (see p. [242]), long established at Liége and other neighbouring towns, competed successfully first with the German and then with the English glass-makers, just as formerly they had competed with the Italians, adopting in turn the methods of each.[[216]]
But in addition to cutting or engraving with a wheel and scratching with a diamond, there is a third method by which the surface of glass may be removed. This is by means of hydrofluoric acid, the only re-agent by which glass is rapidly attacked. The discovery of this acid is usually ascribed to Scheele, the Swedish chemist (born 1742), and a date as late as 1771 is given to the discovery. But there is no doubt that the special virtues of the fumes that are given off when fluor-spar is heated in sulphuric acid were known before this time.[[217]] We have seen how Sandrart, writing before 1675, mentions that his contemporary Henry Schwanhart engraved glass by means of a ‘corrosiv,’ and the statement is repeated with picturesque details by Doppelmayr. By covering part of the glass with a varnish and exposing the rest to these acid fumes, Schwanhart produced a smooth pattern on a dead ground. Certain calligraphic inscriptions on plates of glass, preserved in German museums,[[218]] were probably engraved in this way, but at the time the process did not come into general use. At a much later period hydrofluoric acid has been largely employed in England and elsewhere for engraving on glass. Still more recently this method has given way to the sand-blast. These are both, however, purely industrial processes that have little to do with art.
We have seen how close was the relation in early mediæval times between the quest of the alchemist and the art of the glass-maker—that part of the art above all that was concerned with the production of coloured pastes. So again at the end of the seventeenth century, when the search for the philosopher’s stone, the universal medicine and other such nostrums, had again come into vogue in Germany, the glass-maker’s craft is once more found in close relation with these ambiguous researches. This intimate connection is well illustrated in the history of Johann Kunckel, a man whose career in more than one aspect reminds us of that of Böttger, the discoverer of the secret of making porcelain. Böttger may indeed be regarded as Kunckel’s successor at Meissen and Dresden, for both for a time held official positions as alchemist or arcanist at the Saxon court.[[219]] Kunckel was born in 1638 (or perhaps somewhat sooner) in the duchy of Schleswig. At an early age we find him in the service of the Saxon Elector engaged in the search for the philosopher’s stone. He lectured, too, on chemistry at Wittenberg before a numerous audience. After the year 1677 he entered the service of Frederick William, the Grosse Churfürst. It was at Berlin about this time that his researches upon the transformation of matter led him to make inquiries into the colouring of glass, above all into the mysterious process by which glass could be stained of a crimson or purple tint by means of gold. That such a colour could be thus obtained had long been a tradition among the alchemists. In the old books the secret was dangled before the eyes of the student without being fully explained. The Saracens were probably acquainted with it; Agricola mentions the ritzle, the ‘aurum quo tingitur vitrum rubro colore,’ and Neri refers to the red tint derived from gold.[[220]]
Not a little of the mystery that so long surrounded this ruby colour had its origin, no doubt, in the following facts:—1. The full tint is only to be got when an extremely minute quantity of gold is present. 2. The colour is not developed until the glass is reheated; on first cooling the metal is nearly colourless. It is scarcely necessary to point out how both these properties of the gold pigment must have appealed to the imagination of the alchemists, and have furnished them with arguments in favour of their transformation theories. Here, then, we have one explanation of the interest taken by these early inquirers in the processes of the glass-maker.
In 1679 Kunckel published his Ars Vitraria Experimentalis, a work which is indeed merely a retranslation into German of Merret’s edition of Neri (see p. [219]), with supplementary notes.[[221]] Not that Kunckel here fully discloses the secret of his famous ruby glass—he draws back at the last moment. Orschall, however, his rival, a man of whom we are told that ‘he took to polygamy and other irregularities, and died in a monastery in Poland,’ in his famous tractate Sol sine Veste, first printed in 1684, is somewhat more explicit. A propos of his experiments with certain ‘handsome vases in the style of porcelain,’ he tells us that the milkiness of the glass with which the Oriental porcelain was imitated was only developed on reheating, and the same, he mentions, is the case with the ruby colour of the glass containing gold.[[222]]
Kunckel was settled by the Great Elector on the Pfauen-Insel, near Potsdam, and it was in the glass-houses already erected on the island that, surrounded with the greatest secrecy, he first made his famous ruby glass. After a time, however, constrained by what he calls ‘die lüderliche Verkrämerung des Rubin-Flusses,’ otherwise by lack of gold, he passed over to the service of the Swedish king. He died at Stockholm as Baron Löwenstjern in 1702.
Kunckel’s name has become attached to certain large ewers and beakers of ruby glass. He made, too, glass of a deep emerald tint, but specimens of this are rare. Some of his glasses—and these are perhaps the oldest—are carved in high relief; others are blown with great technical skill. Large sums were given at the time for examples of his work. The vases of blown glass took on classical forms, and were set in scroll mountings of silver gilt. But these mounted pieces are for the most part of later date than Kunckel’s time, for glass of this kind was made at Zechlin and other places near Berlin up to the middle of the eighteenth century and perhaps later. A tankard of ruby glass in the British Museum (Slade, No. 869) bears the cipher of Frederick I. (1701-1713); in the same collection is another fine example (Slade, No. 868), a graceful ewer, set in a rococo silver-gilt mounting.[[223]] Among other specimens of this ruby glass in Lord Rothschild’s collection is a tumbler-shaped beaker, ‘frosted’ on the outside.
As in the case of the porcelain made at a later time in Berlin, the Prussian glass as a whole is distinguished by its technical excellence and, compared at least to the bulk of the contemporary work, by a certain severity of form and decoration.