on the colours used in painting by the Ancients. 1 1 g 
powder of all, and that after this the wall was polished before 
the colour was applied. The stuccos that remain in the ruins 
of the baths of Titus and Livia are of this kind, and so is the 
ground of the Aldobrandini picture; they are beautifully 
white, and almost as hard as marble, and the granular marble 
of different degrees of fineness may be distinguished in them. 
This circumstance indeed offers a test of the antiquity of ruins 
at Rome. In the houses that have been built in the middle 
and later ages, decomposing lava has been mixed with the 
calcareous cement instead of granular marble, and the stuccos 
of these houses are grey or brown, and very coarse in their 
texture. 
Pliny says that purple, orpiment, ceruse, the natural azure, 
indigo, and the meline white, were injured by application to 
wet stucco, which is easily explained in the case of orpiment, 
carbonate of copper, ceruse, and indigo, from their chemical 
composition. 
Vitruvius states that in fresco painting vermilion changed 
if exposed to light, and he recommends the encaustic pro- 
cess for fixing the colour under this circumstance, namely, 
laying over it a coat of punic wax, and liquifying the wax so 
as to make a varnish for the colour. 
Pliny describes this process as applied in painting ships ; 
and we know from his authority that several pictures of the 
great Greek masters were painted in encaustic, and that the 
different colours were laid on mixed with wax. I have exa- 
mined several pieces of the painted stuccos found in the 
different ruins, and likewise the Aldobrandini picture, with a 
view of ascertaining if any application had been made to fix 
me colour ; but neither by the test of alcohol, nor by heat, 
