hydrosulphite

Reductive bleaching is done with sodium hydrosulphite, a powerful reducing agent.

Three common reducing bleaches are sodium bisulphite, sodium hydrosulphite and titanium stripper.

Methaemoglobin was made in a similar fashion, except that two fold molar excess of potassium ferricyanide was used instead of sodium hydrosulphite.

This normally means destroying the dye with powerful reducing agents such as sodium hydrosulphite or oxidizing agents such as hydrogen peroxide or sodium hypochlorite.

Chemical reactions such as oxidation, reduction, pH control are often necessary; even the dissolution process necessitates measuring out appropriate quantities of caustic soda and sodium hydrosulphite in order to achieve reduction.