Coloration

There are a large variety of dyes with differing colour ranges and fastnesses. The choice of dye will be determined by a combination of technical, aesthetic and economic factors. Fastness is particularly important because the colour must withstand the end-use conditions and any aftercare treatments required to maintain the textile. Both the fadeing of colour and staining of adjacent materials are of significance. Standard tests are used to assess colour fastness; in terms of aftercare fastness to washing, bleaching, drycleaning or pressing may be appropriate; in terms of performance fastness to light, rubbing, water (possibly containing salt or chlorine) or perspiration may be more important.

Localised application of colour may be achieved by a number of techniques, including batik, tie-dye and other resist processes but printing is the most important method. The most important commercial techniques at the present time are based on the use of perforated screens. Rotary screen printing is widely used because it is economical and continuous, flat screen, or silk screen printing, is useful for short runs. Roller printing is declining because it is expensive and requires large runs to be economical, although it does allow very fine work to be produced. Essentially printing involves the localised deposition of a dye or pigment in the form of a paste, the colour is then fixed by steaming or baking and then surplus colour and other reagents are washed off.