| [217] | Quite early in the eighteenth century we find an account of a process by which a gas possessing the property of attacking glass may be made by steeping the ‘hesphorus’ or ‘Bohemian emerald’ in spirits of nitre. As we are told that this ‘hesphorus’ when heated emits a green light, we may safely identify it with fluor-spar (fluoride of calcium). |
| [218] | A circular plaque of this character, with a pious inscription, in the Germanic Museum at Nuremberg, has been ascribed to Henry Schwanhart. It is dated 1686 (reproduced by Gerspach, p. 266). |
| [219] | We must remember that at this time little distinction was drawn between the researches of the chemist and the alchemist. |
| [220] | The ruby glass of our old Gothic churches was, however, without exception obtained from copper. But the belief that it contained gold led in France to the destruction of much of this glass at the time of the Revolution. |
| [221] | This book may be best consulted in the French translation, said to be by the Baron D’Holbach (Paris, 1752). Here we have in its final form the little book of Neri, which has passed through the translator’s crucible as many as four times—from Italian to English, then to Latin, to German, and finally to French. For there was, too, an Amsterdam edition in Latin (1668) which came between the English and Kunckel’s version. But, unlike the gold of the alchemist, the work really increased in value during these transformations. Several curious treatises, in the manner of the time, half alchemistic, half scientific, are to be found at the end of the French translation, including a rendering into French of Orschall’s Sol sine Veste. |
| [222] | The somewhat obscure relations of these two men, Kunckel and Orschall, with Cassius, the reputed discoverer of the purple that goes by his name (as well as with the son of the latter), is explained by Beckmann (History of Inventions, vol. i. p. 126). |
| [223] | If in the case of the bottle of ruby glass, with the arms of Saxony and the initials J. G., also from the Slade collection (No. 870), these letters are to be referred to the Elector John George (1656-80), Kunckel must have perfected his invention at an early date. |
| [224] | There is a portrait of her in the National Gallery by Jan Lievens. See, for some account of her strange life, the note in the Official Catalogue (p. 305). Another supposed portrait of this lady in the same collection is by Gerard Dou. |
| [225] | The ‘Beaker with the seasons’ in the British Museum ([Plate XLIII.]) is an example of the more elaborate work of these Dutch designers with the diamond. For though the inscription on this glass is in English, the decoration is undoubtedly by a member of the school of Roemer Vischer. The beaker is dated 1663. |
| [226] | Strictly speaking, the marks on the surface of the glass are rather of the nature of short scratches or dashes than true dots. |