A ceramic or mural decoration made by scratching off a surface layer to reveal the ground WordNet 3.0 & Open English WordNet

Sgraffito is a technique either of wall decor, produced by applying layers of plaster tinted in contrasting colours to a moistened surface, or in pottery, by applying to an unfired ceramic body two successive layers of contrasting slip or glaze, and then in either case scratching so as to reveal parts of the underlying layer. Wikipedia

Painting technique also used for wall or pottery decor Wikidata

A technique in ceramics, art and wall design, where the top layer of pigment or slip is scratched through to reveal an underlying layer. Wiktionary

Technique where the top layer is scratched through to reveal an underlying layer. Wiktionary (translation)