The Collaborative International Dictionary of English v.0.48:

Pipeclay \Pipe"clay`\, v. t.
   1. To whiten or clean with pipe clay, as a soldier's
      accouterments.
      [1913 Webster]

   2. To clear off; as, to pipeclay accounts. [Slang, Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

pipeclay
    n 1: fine white clay used in making tobacco pipes and pottery
         and in whitening leather [syn: pipeclay, terra alba]