Dyeing Process
Most vat dyes, which require a reducing agent to solubilize them, are less suitable than fiber-reactive dyes for amateurs. 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. The dye is soluble only in its reduced (oxygen-free) form. The fiber is immersed repeatedly in this oxygen-free dyebath, then exposed to the air, whereupon the water-soluble reduced form changes color as oxygen turns it to the water-insoluble form.
Indigo is an example of this dye class: it changes from yellow, in the dyebath, to green and then blue as the air hits it.
Not all vat dyeing is done with vat dyes.
Read more about this topic: Vat Dye
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