1) Reducing agent 
Rongalite, also called Rongalit (registered trademark of BASF), is sodium hydroxymethylsulfinate, or Na+HOCH2SO2-. The salt has many names, including also sodium formaldehyde sulfoxylate, and Bruggolite. It is listed in the European Cosmetics Directive as sodium oxymethylene sulfoxylate (INCI). It is water-soluble and generally sold as the dihydra...