Source : Webster's Revised Unabridged Dictionary (1913)

Overglaze \O"ver*glaze`\, a. (Ceramics)
   (a) Applied over the glaze; -- said of enamel paintings,
       which sometimes are seen to project from the surface of
       the ware.
   (b) Suitable for applying upon the glaze; -- said of
       vitrifiable colors used in ceramic decoration.