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.