Thiourea Dioxide is a replacement for Sodium Hydrosulphite / Thiosulphate used in vat dyeing, discharge printing and general colour stripping on cellulose and protein fibres.
Use as an active reducing agent which removes the oxygen from indigo when combined with Soda Ash. Thiourea Dioxide is five times stronger than Sodium Hydrosulphite the alternative reducing agent. See Indigo dye recipe
Use 1 part Soda Ash to 4 parts Thiourea Dioxide and thicken with Indalca PA3R to make a discharge paste for removing some synthetic dyes, especially Procion MX, from cellulose fibres.
Use Thiourea Dioxide as a stripping agent to safely remove most dyes from protein fibres (i.e. wool and silk), as well as cellulose fibres (i.e. cotton, linen and rayon).
Method for Removing Dye Colours
- For 500g of dry fabric use 8 litres warm water, 10g Thiourea Dioxide, 20g Soda Ash and 2.5ml Synthrapol. As wool is sensitive to alkalis, reduce the Soda Ash to 10g.
- Place warm water in a non-reactive dye pot (stainless steel, enamel, or glass – DO NOT USE dye pots or utensils made from cast iron, aluminium or copper). Add Thiourea Dioxide, Soda Ash, and Synthrapol and stir to dissolve.
- Add wetted fibre and stir for one minute.
- Heat rapidly to 100°C for cotton, linen. and rayon (85°C for silk and 90°C for wool).
- Stir intermittently and maintain the temperature for 15-20 minutes (5-10 minutes for wool – be careful not to over agitate the fibre as this will cause felting).
- Cotton can be removed from the pan immediately but wool and silk should be left to cool down in bath.
- Rinse with warm water and neutralise in a solution of Citric Acid (use at a ratio of 5g per litre of water).
A faint smell of ammonia indicates that the Thiourea Dioxide has been exhausted. If this occurs, and not enough colour has been removed, rinse the fibre and repeat the above steps.
The chemical has a shelf life of about two years, if stored in an air tight container. If the material shows a yellowish cast, then it may have lost some of its strength and you may need to use more. Please do a test sample first.
Take care with chemicals: can cause irritation to skin, eyes and respiratory system. Always use in a well ventilated area.
Thiourea Dioxide was previously referred to as Spectralite on this website 02/06/2021
