Zine plates are used in process work of two kinds such as thin zinc with grained surface for photo-lithography and thick zinc with polished surface for etching. Pure zinc is requisite for process work and the plates are perfectly rolled & free from surface blemishes. The thin zinc is used for lithography, chemically treated to free it from grease and is grained in a trough filled with marbles and sand. The thicker zinc is scraped and polished by buffering with abrading. The greasiness is removed by rubbing with pumice powder & water and by passing through a weak acid and aluminum.