Sgraffito

Through color and tone Byzantine potters gave to sgraffito pottery qualities that go beyond the contrasts possible in metalwork. And the history of the colors in their use on Byzantine sgraffito ware again takes us back to Tang China.

Source: wiktionary

Sgraffito is a valuable design technique for working with slips[…], but did you know that this technique has other applications? With leather-hard clay you can incise (cut into) the clay surface. […] To make smooth lines in a raw-glazed surface, first cover the area with liquid wax. Then, using any sharp-edged tool, scratch through the wax and into the glaze, pressing deeply enough to reveal the clay body underneath[…]. When the piece is fired, the wax will burn off and the glaze will pull back from the sgraffito scratches to reveal the underlying clay.

Source: wiktionary

Sgraffito is not only weather resistant but also requires less artistic skill than alfresco painting. Although scratch work was used in Germany from the 13th century (e.g. Magdeburg Cathedral, cloisters), true sgraffito developed in Italy and spread from there. Decoration of a plastered façade with simulated regular stonework existed in Florence from the late 13th century, two-tone decorations from the 15th century. The early sgraffito decorations follow on from the medieval practice of using overlay and ornamentation on buildings and reflect the way in which stone is worked.

Source: wiktionary

[I]n the corner room a sitting platform, 3 ft. broad, as well as a large fireplace, were brought to light, while in the hall (E. iii.), open towards the south, the rough plaster surface of the partly well-preserved east wall proved to be covered with sgraffiti both Tibetan and Chinese.

Source: wiktionary