ii8 Sir Humphry Davy's experiments and observations 
with blacks. Those in the Aldobrandini picture yield oxide 
of iron to muriatic acid, but the darker shades were not 
touched by that acid, nor by solution of alkalies. 
VIII. Of the whites of the Ancients. 
The white colours in the Aldobrandini picture are soluble 
in acids with effervescence, and have the characters of carbo- 
nate of lime. 
The principal white in the vase of mixed colours appears 
to be a very fine chalk. There is another white with a tint 
of cream colour, which is a fine aluminous clay. 
The whites that I have examined from the baths of Titus, 
and those from other ruins, are all of the same kind. 
I have not met with ceruse amongst the ancient colours, 
though we know from Theophrastus, Vitruvius, and Pliny, 
that it was a common colour: and Vitruvius describes it as 
made by the action of lead upon vinegar. 
Several white clays are mentioned by Pliny as employed in 
painting, of which the Parastonium was considered as afford- 
ing the finest colour. 
IX. Of the manner in which the Ancients applied their colours. 
It appears from Vitruvius that the colours used in fresco 
painting were applied moist to the surface of a stucco* formed 
of powdered marble cemented by lime; he states that the 
wall or ceiling had three distinct coatings of stucco made of 
this material, of which the first contained coarse powder of 
marble, the second the finer powder, and the third the finest 
* Lib. vii. Cap. 2, 3> and 4. 
