Dyes and dyeing

Dyes are organic materials used to impart colour to textile fibres. Textiles may be dyed in the yarn or in the piece. Dyes have four important properties:

  • 1) Intense colour.
  • 2) Solubility in aqueous solution (with a few exceptions), either permanently or during dyeing.
  • 3) The ability to be absorbed and retained by the fibre (substantivity) or to be chemically combined with it (reactivity).
  • 4) Fastness, that is the ability to withstand the treatments the fibre undergoes in manufacture and in use.

Until 1856 all dyes were of natural origin, mostly extracted from plants and a few from insects and shell fish. These dyes all belonged to a small number of groups of chemicals and the dyeing process was similar for all but a very few. All museum textiles made before about 1860 have been dyed with natural dyes but very few natural dyes remain in use in any quantity today. Synthetic dyes replaced them remarkably quickly because they were easier to apply, cheap, provided colours unobtainable with natural dyes and shades could be accurately matched from batch to batch. The early synthetic dyes were often of strident colours (mauves and purples) and had very poor light fastness. Subsequently synthetic dyes have been developed to provide an enormous range of colour and intensity for many different purposes - the Colour Index of the Society of Dyers and Colourists contains references to more than 6000 synthetic dyes marketed under 35 000 trade names (Society of Dyers and Colourists, 1971). The first synthetic dyes were applied to natural fibres but whole new classes of dyes have had to be made for use on regenerated and synthetic fibres. The dye chemist is able to modify the dye molecule to give the most satisfactory properties for any particular use.

Dyes are usually classified according to two different classification schemes. One scheme is based on their chemical constitution, the other on the basis of their dyeing properties. However, there is little relation between the two classifications. Azo dyes, for example, may be found among various classifications according to their dyeing properties. The various chemical groups are illustrated by Trotman (1984). Classification according to application, which is most important to the dyer, is as follows:

  • Acid (usually on proteins and synthetics)
  • Azoic (usually on celluloses)
  • Basic/cationic (usually on acrylics)
  • Direct (usually on celluloses and ester celluloses)
  • Disperse (usually on synthetics especially polyester)
  • Mordant/pre-metallized (usually on proteins)
  • Reactive (used on most fibre types)
  • Sulphur (usually on celluloses or ester celluloses)
  • Vat (usually on cellulose)
  • Optical brighteners (for most fibres; they include 'bluing' and fluorescent brighten-ers).

Some textile printing techniques employ dyes rather than inks on fabrics. The science of dyeing and the chemical technology of textile fibres is comprehensively discussed by Trotman (1984). The art and craft of natural dyeing are covered by Bemiss (1973) and by Liles (1990). The history of dyes is reviewed by Taylor and Singer (1956) and in a series of papers on the history of dyes published by the Paper Conservation Institute. Dyes may be identified by wet chemical means using solubility or liquid chromatography techniques (Schweppe, 1979).

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Wood Working for Amateur Craftsman

Wood Working for Amateur Craftsman

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