The technique of scratching through a layer of paint to reveal underlying layers is called sgraffito.
Sgraffito is a subtractive process: an artist applies one coating over another, then scratches, scrapes, or cuts through the upper layer to expose a contrasting colour beneath. On canvas or paper, the tool might be a palette knife, stylus, or other sharp implement. The method can also involve scratching through wet paint to reveal the surface below.
The technique has a long history beyond painting. In wall decoration, artists apply layers of differently coloured plaster and scratch through the upper coat while the surface is still workable. In ceramics, contrasting layers of slip or glaze are applied to unfired clay before designs are incised. The Italian word sgraffiato comes from graffiare, “to scratch,” ultimately related to the Greek graphein, “to write.”
Sgraffito is often confused with impasto, which builds up paint in thick relief, and with fresco, which involves painting on wet plaster. Encaustic is another distinct process, using pigment mixed with heated wax. Because sgraffito removes material rather than merely adding it, it produces crisp lines, revealing marks, and strong colour contrasts.