community of dyers

Sulfur dioxide, SO₂, is the chemical that does the reducing, no matter which of the following chemicals you use to reduce your dye. Originally it was produced by burning yellow sulfur in the presence of the fiber to be bleached. This is probably not a good approach, for your own health; better to use one of the other reducing discharge agents to produce it on the fabric.

Thiourea dioxide, also known as aminoiminomethanesulfinic acid or formamidine sulfinic acid, is sold under the brand names Thiox, Spectralite, and Dharma Dyehouse Color Remover. The chemical formula is H₂NC(=NH)SO₂H. It is used in indigo dyeing and other vat dyeing as well as for discharge. It costs more than sodium hydrosulfite, but you use less.

Sodium hydrosulfite, also known as sodium dithionite, sodium sulfoxylate , and sodium sulphoxylate, is the active ingredient in Rit Color Remover, Tintex Color Remover, Dylon Run away for Whites, and Carbona Run Remover, all of which also contain sodium carbonate (soda ash). (I don't know whather Jacquard Color Remover contains the same ingredients.) Its chemical formula is Na₂O₄S₂. This is the chemical used by Carter Smith in Kate Broughton's book Textile Dyeing: The Step-By-Step Guide and Showcase. Storage of large quantities is unsafe due to its flammability.

Sodium formaldehyde sulfoxylate, also known as sodium hydroxymethanesulphonate, sodium hydroxymethanesulfonate, and formaldehyde sodium sulphoxylate, is the chemical used in Formosul and Rongalite. Its chemical formula is CH₃NaO₃S. It can be used under acid as well as basic conditions.

Although sodium sulfite (Na₂SO₃) and sodium bisulfite (NaHSO₃) are listed in some documents as reductive bleaches, I cannot find a recipe for either's use for this purpose, though it's easy to find recipes for the use of the other reducing agents above. At our level it seems that these are only used to neutralize hypochlorite bleach. Do NOT confuse them with sodium bisulfATE (Na₂SO₄), which is used to destroy cellulose; remember the mnemonic, "bisulfATE ATE my fabric."