The process of adding tin oxide to other ingredients during the glazing of pottery to produce an opaque, white-enameled effect. It was used from c 1000 BC by the Assyrians; in the 8th-9th centuries AD, Persian and Islamic potters rediscovered the technique and it was transmitted to Spain, Italy, France, and Holland. Tin glaze was probably first used to hide faults of color in the body, for most clays contain a variable amount of iron that colors the body from buff to dark red. Tin-glazed wares look somewhat as though they have been covered with thick white paint.