sinopia

Noun

1. A reddish-brown ochre-like pigment, derived from sinople, used in traditional oil painting and as the cartoon for frescos.

   Synonyms: sinoper

2. The rough sketch (executed in sinopia) which underlies a fresco.
   • Today many of the sinopias have been uncovered by a method called stacco. - 1985, Joseph Reese Strayer, Dictionary of the Middle Ages:
   • In the course of lifting the frescoes from the walls the restorers discovered Simone's full-scale working drawings (in red chalk made from iron oxide and known as sinopie) which lay directly beneath the painted plaster...