of Lapis Lazuli, ami on artificial Ultramarine. 245 



Whether it be in consequence of a lessened demand, and con- 

 sequent diminished manufacture since the discovery of prussian 

 blue, and other cheaper blues, or in consequence of a dimi- 

 nislied importation of the lazure-stone, that this colour has 

 become so very scarce, this much is certain, that its high 

 price (an ounce of the best quality being said to sell now at 

 from one hundred to two hundred francs*) has gready limited 

 its use ; whilst formerly, especially in the sixteenth century, it 

 was almost wasted by painters, as is proved by many pictures 

 of that period. 



The value of the colour naturally led to a desire of pro- 

 ducing it artificially. Some assert, that the art was known in 

 the sixteenth century, but kept secret. But this probably im- 

 plied only the art of obtaining ultramarine of the best quality 

 from the lazure-stone. What are called artificial lazure-stones, 

 for the production of which there are many formulasf , are in fact 

 artificial pieces of glasses coloured with some metallic oxide 

 (mostly oxide of cobalt), which will of course yield no ultrama- 

 rine. Indeed the colour of lapis lazuli was generally ascribed, 

 until lately, from the results of chemical analyses, and according 

 to analogy, fi-om a metallic oxide (oxide of cobalt, copper, iron, 

 &c. supposed to be contained in it). Wallerius derives it from 

 silver J, which, however, has not been found by any modern 

 chemist, and which was probably only believed to be it through 

 a well-known mistake usual in former times. The common opi- 

 nion, however, was, that the blue colour of the mineral was 

 l)roduced by oxide of copper, until it was shown by Marggraf, 

 that the lazure-stone contained oxide of iron only, and no 

 oxide of copper §. It was his analyis which gave the first ex- 

 planation of the component parts of this stone ; for the ac- 

 counts of llinmann and Cronstedt are not sufficiently defined. 

 Klaproth's subsequent analysis || generally confirms the re- 

 sults of that of Marggraf, except that he points out a portion 

 of alumina which the latter overlooked ; tor the rest, he also 

 inclined to the opinion that the blue colour was produced by 

 the oxide of iron. It was Guy ton de Morveau who first drew 

 public attention to a portion of potash contained in the Inzure- 

 stone, and which he thought accidental, but considered that it 



* Leuchs's Farben-imd Fdrbckiindc, p. 205. Tlienard Trailu dc Chimic, 

 toin. ii. (C18) p. 210. 



t Compare some of them in Lciiclis, p. 487. 



t System. Mineral, i. 312. 



^ See his Chemical works, vol. i. p. 121-134, and Hochhcimer's Chcm. 

 Mincralogie, vol. i. [). 2.'5!)-244. 



II See JteUrU^ic, &c. vol. i. p. 180-19(5, and Schvveigger's Journal, vol. xiii. 

 |i. 4H8. xiv. p. ."j.'M. and xli. p. 2:54. lie roiiml silica and alumina, car- 

 Iwnutc ul'liine, sulpliule oC liine, and oxide of iron. 



was 



