Source : Webster's Revised Unabridged Dictionary (1913)

Wet plate \Wet plate\ (Photog.)
   A plate the film of which retains its sensitiveness only
   while wet. The film used in such plates is of collodion
   impregnated with bromides and iodides. Before exposure the
   plate is immersed in a solution of silver nitrate, and
   immediately after exposure it is developed and fixed.