Mainly used to colour cellulose, such as cotton, yarns or cloths made from cellulose yarns. Vat dyes are insoluble in water so they require to be made soluble before dyeing the fibre. Using an alkaline solution of caustic soda and sodium hydrosulphite the dye is converted, by chemical reduction, to a leuco alkali-soluble. At this point the colour will differ from the final dyed colour. The dye, having entered the fibre, is exposed to air which oxidizes the dye in the fibre back to its insoluble state. This is a dyeing process when the dye is accepted into the fibre in a reduced or vatted form, when oxidized the colour is fixed firmly to the fibre. The basic principles of vat-dyeing are:
- The conversion of the insoluble vat dye into the soluble sodium-leuco form by reduction or vatting.
- The conversion of the absorbed dye, in the cloth or yarn, back to the insoluble state by oxidation.
- Dyed or printed yarn or cloth treated in a hot detergent bath to produce a stable shade with maximum fastness.
Indigo is a natural vat dye and has been used extensively in India and west Africa for many centuries.
A type of rib knitting machine with two needle beds with the hooks from each bed facing each other, both beds forming an inverted V.
A pile fabric where the loop, created by an extra warp is cut. The distinguishing feature of velvet is a succession of rows of short, close together, cut tufts creating a uniform surface which is lustrous in appearance and soft to the touch. The quality of velvet is determined by the closeness of the tufts and the density of the backing. Traditionally woven with silk pile and cotton back as a single fabric. Can be mechanically woven as a double, face to face, cloth and cut down the centre in the same way as Wilton carpet. There are many types of velvet with names like: chiffon velvet, Lyon velvet, façonne velvet, panne velvet and brocade velvet. A wide range of uses include: dresses, jackets, shoes, hats, upholstery, curtains and in industry.
A 100% cotton velvet made in Manchester, England in the early eighteenth century. Constructed with a weft float, which is then cut to form the pile, from mercerized cotton yarns, although rayon was also used. The pile slopes slightly to emphasise the sheen of the yarn and create a lustrous surface to the cloth. Used for clothing and as a furnishing.