Definitions for underglazeˈʌn dərˌgleɪz
Random House Webster's College Dictionary
(of a color or decoration) applied to a ceramic piece before the glaze.
(n.)color or decoration so applied.
Origin of underglaze:
A decorative slip applied to the surface of pottery before glazing.
applied under the glaze, that is, before the glaze, that is, before the glaze is put on; fitted to be so applied; -- said of colors in porcelain painting