CHAP. 20.—USTA.
Usta[1] was accidentally discovered at a fire in the Piræus,
some ceruse having been burnt in the jars there. Nicias, the
artist above-mentioned,[2] was the first to use it. At the
present day, that of Asia, known also as "purpurea," is considered
the best. The price of it is six denarii per pound. It
is prepared also at Rome by calcining marbled sil,[3] and
quenching it with vinegar. Without the use of usta shadows
cannot be made.[4]
1. "Burnt" ceruse. This was, in fact, one of the varieties of "minium,"
red oxide of lead, our red lead. Vitruvius and Dioscorides call it "sandaraca,"
differing somewhat from that of Pliny.
2. In Chapter 10.
3. See B. xxxiii. cc. 56, 57.
4. It was possibly owing to this that the colour known as "umber" received
its name, and not from Ombria, in Italy. Ajasson says that shadows
cannot be successfully made without the use of transparent colours,
and that red and the several browns are remarkably transparent.