on the Colours used in Vainting ly the Ancients. 2C.S 



Plinv, which was our minima, and imperfectly decomposed ceruse, 

 or pale massicot. 



The yellows in the Aldobrandini picture are all ochres. I ex- 

 amined the colours in a very spirited picture, on the wall of one 

 of the houses at Pomj^eii, of a lion and a man ; they all proved 

 to be red and yellow ochres, 



W. Of the Blue Colours of the Ancients. 

 Different shades of blue are used in the different apartments 

 of the baths of Titus, and several very fine blues exist in the mix-, 

 tures of colours to which I have referred in the last two sections. 



These blues are pale or darker, according as they contain 

 larger or smaller quantities of carbonate of lime ; but wlicn this 

 carbonate of lime is dissolved by acids, they present the same 

 bodv colour, a very fine blue powder f^imilar to the l)est smalt 

 or to ultramarine, rough to the touch, and which does not lose 

 its colour by being heated to redness ; but which becomes ag- 

 glutinated and semifused at a white heat. 



This blue I found was very little acted on by acids. Nitre- 

 muriatic acid by being long boiled upon it gained, however, a 

 slight tint of yellow, and afforded proofs of the presence of oxide 

 of copper. 



A quantity of the colour was fused for half an hour with twice 

 its weight of hydrate of potassa ; the mass, which was blueish 

 green, was treated by muriatic acid in the manner usually em- 

 ployed for the analysis of siliceous stones, when it afforded a 

 quantity of silica equal to more than 3-5ths of its weight. ^ The 

 colouring matter readily dissolved in solution of ammonia, to 

 which it gave a bright blue tint, and it proved to be oxide of 

 copper. The residuum afforded a considerable quantity of aiu- 

 niine, and a small quantity of lime. 



Amongst some rubbish that had been collected in one of the 

 chambers of the baths of Titus, I found several large lumps of a 

 deep blue frit, which when powdered and mixed v/ith chalk pro- 

 duced colours cxactlv the same as those used in the baths, and 

 which when submitted to chemical tests were found to be the 

 same in composition. 



The minute quantity of lime found in this substance was not 

 sufficient to account for its fusibility: it vvas therefore reasonable 

 to expect the presence of a fixed alkali in it ; and on fusing some 

 of it with three times its weight of boracic acid, and treating 

 the mass with nitric acid and carbonate of ammonia, and after- 

 wards distilling sulphuric acid from it, I procured from it sul- 

 phate of soda; which proves that it was a frit made by means of 

 soda, and coloured with oxide of copper. 



The undiluted colour in its form of frit is u^cd for ornamenting 

 '£ 2 some 



