Slip (ceramic surface)

Slip is a liquid suspension of clay used in ceramic processes and decoration. A slip layer may change the visible ground on which ornament is applied. Glaze is a different surface system, forming a vitreous coating in firing. A light-coloured ground therefore should not automatically be called white glaze.

The Nishapur bowl’s catalogue describes yellow slip and green decoration beneath transparent glaze. Another Iranian bowl in the library is described as painted on opaque white glaze. Retaining the exact wording makes the comparison more useful than grouping both as the same painted pottery.

The medium field does not provide every firing temperature, ingredient or workshop stage. A photograph can show colour and arrangement but cannot independently identify a body’s mineral composition or a colourant. Avoid making a manufacturing recipe from a catalogue sentence.

Damaged or restored surfaces can complicate visible layers. Existing chips should not be enlarged to look for slip, and no scraping test should be attempted. A condition report, technical catalogue or specialist examination is the appropriate source for detailed layer identification. Contemporary maker documentation can explain a current process without being transferred to a medieval object.