Milk Glass is a term used by glass-makers for opaque white glass.
Milk glass looks like white porcelain.
It was first made in Venice in the 14th or 15th century, and later in just about every country that made glass. The opaque white colour is usually made with tin oxide. During the 17th and 18th centuries it was very popular, and during that period it was often decorated with enamel painting. This is the kind of white glass that is usually collected by milk glass collectors. It has to be opaque and white.