I shall remark, in the last place, that the manufacturing of vessels and ornaments of every kind from solid fluor-spar was begun in Derbyshire in the year 1765[229]. The articles formed of it are in England called spar ornaments, and sometimes _blue John_. Many beautiful colours must, as is said, be brought forward by means of fire. But the heat must be applied with great caution; for fluor-spar, as is well known, by a strong and particularly a sudden heating, cracks, and loses its transparency. Since writing the above, I find that M. Raspe[230] denies this bringing forward of colours by fire. FOOTNOTES [204] Mariette, Traité des Pierres gravées. Par. 1750, fol. [205] The two ancient glasses found at Nismes, and described in Caylus’ Recueil d’Antiquités, ii. p. 363, were probably of this sort. [206] Natter, Traité de la Méthode antique de graver en Pierres fines, comparé avec la Méthode moderne. Lond. 1754, fol. [207] Of this kind were the _calices audaces_ of Martial, xiv. 94, and those cups which often broke when the artist wished to give them the finishing touch. [208] See Sandrart’s Teutsche Akademie, vol. i. part 2, p. 345, where there is much valuable information respecting the German artists. Compare also Doppelmayer’s Nachricht von Nürnberg. Künstlern. [209] Oculus Artificial. iii. p. 79. [210] Lib. xxxvii. [211] Cap. 52, p. 59. [212] Origin. xvi. 8. [213] De Miner. lib. ii. 2. [214] Traité des Pierres gravées, i. pp. 90, 156. [215] Ibid. p. 156. [216] In the preface, p. 15. [217] Ueber den Nutzen d. geschnitt. Steine. Altenb. 1768, p. 42. [218] Le Veil, iii. p. 19. This anecdote however is not mentioned by Mezeray, Castelnau, or Laboureur; and Bayle must have been unacquainted with it, or he would have introduced it into his long article on the Duchesse d’Estampes. [219] Doppelmayer, p. 232. [220] Abhandlungen der Schwed. Akad. xxxiii. p. 122. [221] Halle, Fortgesetzte Magie. Berlin, 1788, 8vo, i. p. 516. This author says that the invention came from England, where it was kept very secret; but the honour of the second invention belongs to H. Klaproth. [222] Schwanhard, by the acuteness of his genius, proved what was before considered as impossible, and found out a corrosive so powerful that the hardest crystal glass, which had hitherto withstood the force of the strongest spirits, was obliged to yield to it, as well as metals and stones. By these means he delineated and etched on glass, figures of men, some naked and some dressed, and all kinds of animals, flowers, and plants, in a manner perfectly natural; and brought them into the highest estimation.--Sandrart, Teutsche Akademie, i. 2, p. 346.--Doppelmayer, p. 250, says, “After 1670 he accidentally found out by the glass of his spectacles, upon which some aquafortis had fallen, becoming quite soft, the art of etching on glass.”