This washer has the Chinese characters "SHUFU" molded onto it.  Porcelain items carrying the Shufu characters are considered imperial porcelain. The majority of Shufu items are generally small daily use items for daily, such as plates and bowls. Vases, jars, and larger items are less frequent.
 
Shufu wares are a type of porcelain specifically made at the Hutian kiln during the Yuan dynasty. This type of porcelain has an appearance similar to "qingbai" or white porcelain, but has an off-white color with a very opaque glaze. The glaze of Shufu porcelain is completely non-reflective. This is sometimes described as a "candle wax" appearance. Together with an impressed porcelain decoration that is protruding from the base material, these features allow for easy recognition of Shufu ware.