The Collaborative International Dictionary of English v.0.48:

Depolishing \De*pol"ish*ing\ (d[-e]*p[o^]l"[i^]sh*[i^]ng), n.
   (Ceramics)
   The process of removing the vitreous glaze from porcelain,
   leaving the dull luster of the surface of ivory porcelain.
   --Knight.
   [1913 Webster]