Glaze

A term used in ceramics to describe a thin coating of minerals which produces a glassy transparent or colored coating on bisque ware. Typically applied either by brushing, dipping, or spraying, it is fixed by firing the bisque ware in a kiln. This makes the surface smooth, shiny, and waterproof.

Also, a glaze can be a thin, translucent or transparent coat over a painting, sometimes meant simply to protect the paint underneath, but more often to add a veil of colouration to an area of a picture. (artlex.com)

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