He would start with a stenciled acrylic underpainting and finish by making marks with the chalk and charcoal shells.
Source: wiktionary
Underpainting
Synonyms for "underpainting"
Ranked by relevance and common usage.
Sample sentences
2 total sentences available.
At first they wouldn't believe him, but he gave them proof. X-ray the Adulteress, he told them, and you will find an underpainting. They did and found the underpainting van Meegeren had described.
Source: wiktionary