Vat dyeing
Also known as: Vat dyeing
Two-stage dyeing with water-insoluble dyes that become soluble in an alkaline reduction bath and precipitate back onto the fibre after oxidation.
Description
Vat dyeing uses water-insoluble dyes with a quinoid structure (indigoids, anthraquinone, naphthalene and perylene derivatives). In the first step the dyes are reduced with sodium dithionite under alkaline conditions (caustic soda, pH 12-13) to the water-soluble leuco form. In this form the dye penetrates the fibre.
The second step is oxidation in air or with hydrogen peroxide, which precipitates the original dye back inside the fibre where it is mechanically trapped. The bond is purely physical, yet vat dyes achieve outstanding light and wash fastness.
Classic vat dyes include indigo (denim), Indanthren (BASF, since 1901) and thioindigo. The process is chemically demanding and expensive but is used for corporate wear and denim textiles because of its unique colour depth and durability.
Properties
| Chemistry | Reduction with dithionite, reoxidation |
|---|---|
| Fibre suitability | Cotton, viscose, linen |
| Fastness | Outstanding light and wash fastness |
| Application | Denim, corporate wear, workwear |
| Cost | Higher than reactive dyeing |
Related product categories
Sources & references
1- Wikipedia: Küpenfarbstoff Wikipedia — Freie Enzyklopädie https://de.wikipedia.org/wiki/K%C3%BCpenfarbstoff
