Aqueous formulations comprising (A) at least one organic complexing agent selected from (A1) alkali metal salts of aminopolycarboxylic acids and (A2) polymers bearing at least two —CH2—N(CH2COOH)-units per molecule, partially or fully neutralized with alkali, (B) at least one salt of at least one of the following acids: nitric acid, sulphuric acid, sulphamic acid, methanesulfonic acid, C1-C2-carboxylic acids, C2-C4-hydroxymonocarboxylic acids, C2-C7-dicarboxylic acids, unsubstituted or substituted with hydroxyl, and C4-C6-tricarboxylic acids, each unsubstituted or substituted with hydroxyl, (C) at least one compound selected from (C1) phosphoric acid C2-C10-monoalkyl esters, (C2) a C3-C10-alkynol, optionally alkoxylated with one to 10 alkoxide groups per hydroxyl group, and (C3) a C4-C10-alkynediol, optionally alkoxylated with one to 10 alkoxide groups per hydroxyl group, said aqueous formulations having pH values in the range of from 7.5 to 10.