The Collaborative International Dictionary of English v.0.48:

Almagra \Al*ma"gra\, n. [Sp. almagra, almagre, fr. Ar.
   al-maghrah red clay or earth.]
   A fine, deep red ocher, somewhat purplish, found in Spain. It
   is the sil atticum of the ancients. Under the name of
   Indian red it is used for polishing glass and silver.
   [1913 Webster] Almayne
   Almain