on the Colours used in Paint'wg by the Ancients. 415 



a deep-coloured rose: and in painting, he states that it was laid 

 on to give the last lustre to the sandyx, a composition made by 

 calcining together red ochre and sandarach, and which therefore 

 must have been nearly the same as our crimson. 



In the batlis of Titus there is a broken vase of earthenware, 

 Avliich contains a pale rose colour ; where it has been exposed 

 to air, it has lost its tint, and is become of a cream colour, but 

 the interior has a lustre approaching to that of carmine. 



I have made many experiments on thin colour. It is destroyed 

 and becomes of a red brown by the action of concentrated acids 

 and alkalies ; but dilut!s.'d acids dissohe a considerable quantity 

 of carbonate of lime with which the body colour is mixed, and 

 leave a substance of a bright rose colour: this substance when 

 heated first blackens, and when urged with a strong flame be- 

 comes white ; and treated with alkali, proves to be composed of 

 siliceous, aluminous, and calcareous earths, with no sensible 

 quantity of any metallic substance, except oxide of iron. 



I endeavoured to discover if the colouring matter was com- 

 bustible. It was gradually heated in a glass tube filled v>ith 

 oxygen; it did not inflame, but became red hot sooner than it 

 would have done had it been merely earthy matter : on exposing 

 the gas in the tube to lime-water, there was a precipitation of car- 

 lionate of lime. Some of it was mixed with hvperoxymuriate of 

 potassa, and heated in a small retort; when the salt fused there 

 was a sHght scintillation, a little moisture appeared, and the gas 

 given off received inta lime-water occasioned a very evident pre- 

 cipitation. 



It appeared from these experiments, that the colouring matter 

 was a compound of either vegetable or animal origin. I threw 

 some of it upon a hot iron : it emitted scarcely any smoke, and 

 gave a smell which had some resemblance to that of prussic acid, 

 but which was extremely faint. 



When hydrate of potassa was fused in contact with it, the 

 vapours that rose had no distinct am.njoniacal smell ; they gave 

 indeed slight fumes to paper moistened vvith muriatic acid, but 

 this is far from being an unequivocal proof of animal matter. 

 I compared this colour with vegetable lake from madder, and 

 animal lake from cochineal diluted to the same degree as nearly 

 as could be judged, and fixed upon clavs. The lake of madder, 

 after being dissolved in strong muriatic acid, had its colour re- 

 stored by alkalies, which was not the case with the ancient lake. 

 The lake of madder likewise gave a much deeper lint to inuriatie 

 acid, and produced a tawny hue when its weak inuiialic solution 

 was acted on i)y muriate of iron ; whereas the ancient !. ke did 

 not change in colour. The ancient lake agreed with tiic lake 

 of cochineal in being rendered of a deeper hue by weak alkalies, 



and 



