sinopia

noun

1. (countable, uncountable)A reddish-brown ochre-like pigment, derived from sinople, used in traditional oil painting and as the cartoon for frescos.
2. (countable, uncountable)The rough sketch (executed in sinopia) which underlies a fresco.

   “Today many of the sinopias have been uncovered by a method called stacco.”

   “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 [...].”