the stability of an acidic liquid cleaner for aluminum comprising mineral acid , oxidant , polyvalent metal ions , and surfactant is substantially improved by the presence in the cleaner of from 0 . 05 to 5 g / l of a component selected from the group of glycols containing from 2 to 10 carbon atoms per molecule and mixtures of such glycols . the effectiveness of the cleaner for primary cleaning and de - smutting of aluminum and its alloys is not impaired and may even be improved by the addition of the glycol component .