Abstract: An etching bath for printing plates of magnesium or alloys thereof comprising: aqueous nitric acid; a sulfated fatty acid ester; 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; a polyhydric alcohol of from 2 to 10 carbon atoms or an ether derivative thereof; a second saturated or olefinically unsaturated carboxylic acid which comprises at least one hydroxy-unsubstituted monocarboxylic acid of from 8 to 24 carbon atoms; and an alkylarylsulfonate. A concentrated additive comprising all of the foregoing bath ingredients except the aqueous nitric acid, to which water and nitric acid are added to provide a powderless etching bath. A method for etching printing plates of magnesium or alloys thereof using the foregoing bath formulation.