Lithographic printing plate from silver halide emulsion

Claim 1

In a method for making a lithographic printing plate, which comprises exposing a photosensitive material including a silver halide emulsion layer, and developing the exposed material, the improvement comprising making an undeveloped silver halide portion of said silver halide emulsion layer receptive to oleophilic inks by treating the developed material either (1) simultaneously with at least one solvent for silver halides and at least one organic mercapto or thion compound selected from the group consisting of compounds having the formulae (I), (II) and (III): ##STR3## wherein R is alkyl having at least 10 carbon atoms, aryl or aralkyl group R' is hydrogen, an alkyl having not more than 12 carbon atoms, aryl or aralkyl group, and Z is an atomic group required to form a 5- or 6-membered heterocyclic compound together with N and C in the formulae, or (2) successively, first with said solvent and second with said organic mercapto or thion compound, said organic mercapto or thion compound being capable of forming a compound which is more stable and has a lower solubility than a soluble silver complex formed by said solvent to make an undeveloped silver halide portion receptive to oleophilic inks.