A Chinese brush washer, oil-spotted celadon pottery, 19th century

Oil-spot glaze, also known as “temmoku” or “tenmoku,” is a type of glaze used in ceramic art that originated in ancient China. It is characterized by its rich, glossy surface with distinctive dark spots resembling drops of oil. These spots are created during the firing process when iron oxide in the glaze forms clusters or crystals, resulting in the unique speckled appearance.

Oil-spot glaze was traditionally used on tea bowls and other vessels in Chinese ceramics, particularly during the Song Dynasty (960-1279) and later periods.

The name “temmoku” is derived from Tianmu Mountain in China’s Zhejiang Province, where tea bowls with oil-spot glaze were originally produced. Over time, oil-spot glaze became popular in other regions of China and was also adopted by ceramic artists in Japan and Korea.