486 Scientific Proceedings, Royal Dublin Society. 



sienna, a bright red, a yellow (largely used), a neutral green, an 

 emerald green, two Hues, a lilac, and a reddish purple. The 

 yellow is much employed in filling up finely-traced designs. The 

 black of course is lampblack, or possibly fish-bone black, that is 

 to say, charred fish-bones, or some other form of carbon artificiall}'' 

 prepared, in a finely-divided state. The reds, the yellow, the 

 greens, and the blues could be obtained either — first, by grinding 

 natural mineral substances ; second, by grinding artificially coloured 

 enamels or glasses. The very appearance of the ■ colours is in 

 favour of the first rather than the second, and altogether against a 

 third, possible process of preparation, namely, by the formation of 

 those substances known as lakes which are precipitates of vegetable 

 or animal pigments in combination with alumina or lime. By 

 making comparisons with ground minerals, I conclude that the 

 bright red is realgar (arsenic disulphide, Asz S2) ; the yellow is 

 orpiment, auripigmentum, the gold colour of the ancients (arsenic 

 tersulphide, Asj S3) ; and the emerald green is malachite, an ore of 

 copper (basic carbonate of copper, CuaCos'CuHsOz). The deep 

 blue might be lapis-lazuli, the natural ultramarine, but I am in- 

 clined to think not, for the following reason : where the green is 

 enhanced in beauty by an overlying coat of blue, the effect is that 

 of a transparent pigment, such as could not be produced by lapis- 

 lazuli. The reddish purple, I am of opinion, is either a finely 

 ground glass coloured with gold, or a preparation similar to that 

 known as the purple of Cassius. Its very sparing use must not 

 be overlooked, and may be justly regarded as an evidence of its 

 costly nature. It is not alone that it is employed in a few places, 

 but it is put upon the vellum in very thin washes. 



I have sought for information concerning the colours used by 

 the ancients, for the reds and yellows recalled to mind the colours 

 of Egyptian and Assyrian decorative paintings. There are three 

 or four works which deal with this subject : Sir Humphrey Davy's 

 Paper in the Philosophical Transactions of the Royal Society for 

 1814, on colours employed by the painters who executed the frescoes 

 on the walls of the Baths of Titus and the houses of Pompeii ; 

 Dr. Thomas Thomson's History of Chemistry, vol. i., p. 77, pub- 

 lished in 1830 ; and a recently published Paper by M. Berthelot, 

 " SiTr les Notations Alchimiques," in the Annales de Chiniie et de 

 Physique, 6th series, vol. iv., p. 370 ; also a work by the same author, 



