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.