De-rusting chemicals are the blended acids. These acids react with metal to form the respective ferric salt and the evolution of hydrogen gas. During the reaction, the metal is dissolved in the acid bath. A fine layer is stripped from the surface. Thus making it free from the contaminants adhered on the surface of the metal. The dissolution rate depends on the concentration of the chemical, time and the temperature of the bath.

The free ferrous ions in the bath consume the acid strength in the proportion. It is very necessary to control the iron content of the bath to get the desired results. Iron content can be controlled by dilution or total discardation of the bath. Periodic de-sludging of the bath will help in better bath life. White towel test’- Wiping a white towel across clean & dry surfaces.