Abstract: A process and compositions for detecting improperly processed areas in heat treated aluminum are disclosed. A solution containing an acid or a base and an oxidizing agent and, if desired, a color enhancing ingredient is applied to an aluminum object to produce a color difference between those areas of the surface of the object which have been properly hardened and the areas resulting from improper heat treatment. The solution can be applied to the aluminum by brushing, swabbing, immersion or spraying. The acid or base in the solution attack the aluminum surface so that the oxidizing agent in the solution can react with the aluminum to produce the aforementioned color differential.