Process solution and method for making a lithographic aluminum offset plate by the silver salt diffusion transfer process

A method for making an offset printing plate according to the silver salt diffusion transfer process comprising the steps of:

• information-wise exposing an imaging element comprising in the order given (i) a hydrophilic base, (ii) an image receiving layer containing physical development nuclei and (iii) a silver halide emulsion layer,
• developing said information-wise exposed imaging element using an aqueous alkaline processing solution in the presence of at least one developing agent and at least one silver halide solvent other than sulfite to obtain a silver image on said hydrophilic support, and
• removing said silver halide emulsion layer and any optional layer on top of said silver image to expose said silver image by means of washing with rinsing water, said offset printing plate having a uniform good quality with respect to maximum density, gradient, good ink acceptance in the printing areas, no ink acceptance in the non-printing areas and no sticking of the emulsion layer during mechanical processing of said offset printing plate, wherein said alkaline processing solution contains aluminum ions in an amount of at least 0.3 g/l and sodium sulfite in an amount ranging from 60 to 160 g per liter.