Abstract: Described is an improved process for effectively cleaning metal surfaces. This method includes applying to the metal a bath liquid having at least one surfactant and at least one alkaline salt, periodically monitoring the concentration of the surfactant in the bath liquid, and adding additional surfactant to the bath liquid as needed to provide the necessary concentration while maintaining the concentration of the alkaline salt constant. The periodic monitoring is performed by an extraction test, where the extracted sample is then subjected to a light absorbance test. Once the concentration has been determined, sufficient surfactant is added to the bath liquid to restore the concentration to its optimum level. Also described is a method for complexing the oil which has been removed from the metal with an additional surfactant additive to form a complex compound which has a density less than that of the bath liquid. The oil-surfactant compound rises to the top of the bath and may be skimmed off.