The Collaborative International Dictionary of English v.0.48:

Pottern \Pot"tern\, a.
   Of or pertaining to potters.
   [1913 Webster]

   Pottern ore, a species of ore which, from its aptness to
      vitrify like the glazing of potter's wares, the miners
      call by this name. --Boyle.
      [1913 Webster]