The Collaborative International Dictionary of English v.0.48:

Vulcanization \Vul`can*i*za"tion\, n. [See Vulcan.]
   The act or process of imparting to caoutchouc, gutta-percha,
   or the like, greater elasticity, durability, or hardness by
   heating with sulphur under pressure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vulcanization
    n 1: process of treating rubber or rubberlike materials with
         sulphur at great heat to improve elasticity and strength or
         to harden them [syn: vulcanization, vulcanisation]