Sodium Hydrosulfite (or "Hydro") is a universal reducing agent that is used for indigo dyeing. It is also used as a non-aggressive alternative to bleach for removing color from dyed fabrics and for whitening antique textiles.
For use with Jacquard’s Pre-reduced Indigo: use 1 part Indigo Dye : 2 parts Sodium Hydrosulfite : 4 parts Soda Ash. (Use 1 gal/3.79 L of water for every 0.18/5 g of dye.)
For use as a color remover: use in equal parts with Soda Ash (1:1) at 3-5% by dry weight of fabric. Heat to 185°F/85°C, add fabric and continue heating. Color removal works best at a rolling boil. Keep fabric moving for 10 to 20 minutes or until color has left as desired. Wash with mild detergent in cool water.
Note: not all dyes are fully susceptible to color removal. Results may vary. Test first when possible.
CAUTION: Harmful if swallowed. Give water or milk if swallowed and call a physician. Avoid contact with eyes. Keep out of reach of children. Do not expose to excessive heat.