Powderless etching method for magnesium printing plates

A process for powderless etching of photoengraving plates of magnesium or magnesium alloy which comprises:

• a. preparing an etching bath which comprises water and, per liter of bath,
• A. from about 70 grams to about 360 grams of 42.degree. Baume nitric acid,
• B. from about 0.25 gram to about 5 grams of a sulfated fatty acid ester having from 10 to 24 carbon atoms in the acid moiety and from 1 to 12 carbon atoms in the alcohol moiety,
• C. from about 0.25 gram to about 6 grams of a first saturated or olefinically unsaturated carboxylic acid which comprises a hydroxy-unsubstituted monocarboxylic acid of from 2 to 6 carbon atoms, or a polycarboxylic or hydroxy-substituted monocarboxylic acid of from 2 to 8 carbon atoms,
• D. from about 2 grams to about 25 grams of a polyhydric alcohol of from 2 to 10 carbon atoms or an ether derivative thereof,
• E. from about 2 grams to about 15 grams of a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxy-unsubstituted monocarboxylic acid having from 8 to 24 carbon atoms, and
• F. from about 0.25 gram to about 4 grams of an alkylarylsulfonate selected from the group consisting of the alkylbenzenesulfonates wherein the alkyl portion contains from 8 to 18 carbon atoms and the alkylnaphthalenesulfonates wherein the alkyl portion contains from 3 to 18 carbon atoms;
• b. maintaining said bath at from about 100.degree.F. to about 115.degree.F;
• and
• c. contacting a plate bearing a photoresist coating image with a said bath until the uncoated portions of the plate have been etched to a satisfactory depth.