These synthetic vat dyes colour natural fibres (not recommended for wool) through a process of oxidization and reduction. They are extremely strong dyes and their washfastness and colourfastness are excellent. Reduction is achieved at a temperature of 120° – 160° F. Cloth immersed in this dye will develop the true dye colour once removed from the bath and exposed to the oxygen in the air. Vat Dyes may also be used as a ‘discharge dye’. They will effectively remove specific dyes from previously dyed cloth and replace it with its own colour. This is very useful when using resist techniques like shibori.
To dye with Vat dyes you will need Thiourea Dioxide as a reducing agent and Lye to raise the pH of the vat.