Introduction and the role of testing 1
The colourist and colour quality 15
The chemical principles of coloration 27
The attributes of fibres 44
The selection, classification and application of dyes 76
Industrial coloration methods 112
The modern approach to coloration 138
Practical notes 158
1 Some examples of commercial dyes 166
2 Generic names of synthetic fibres 171
For many years the Society of Dyers and Colourists has been aware of the need for a book covering the basic science and technology of textile coloration for the benefit of readers without a detailed scientific background. In the mid-1980s the late Dr Frank Jones of the University of Leeds started to write such a book, but sadly he died before he could complete this worthwhile task. The torch was then passed to me, with the brief to prepare a work for those who probably lack science qualifications at A-level but who nevertheless need to become familiar to some extent with the work of the professional colourist. The target readership included people working in nontechnical capacities in industry, and students of home economics, textile design and management. The aim is to introduce such readers to the relevant technological background and the basic principles of coloration, and show how colour is assessed objectively in modern industry. I am grateful to several people for their assistance, including Paul Dinsdale (the Society’s editor), Jean Macqueen, for her expert editorial work on the manuscript and index, and Carol Davies, for painstaking typesetting and layout. I also acknowledge the Textile Institute, Manchester, for permission to reproduce Figures 4.12, 4.13, 6.7, 6.9, 6.10 and 6.12, and Miss B Lomas of the Textile Technology Department, UMIST, Manchester, for permission to reproduce Figures 4.1 and 4.2, and for kindly providing suitable copies.
Introduction and the role of testing
The pleasure derived from imparting colour to clothing has existed since the time of the earliest civilisations; a world of fashion without colour is impossible to imagine. Coloration processes produce the most visible results of all the finishing operations carried out during the preparation of textile goods. As such they reveal both the care taken with the coloration and the degree of control exercised during other stages of the manufacturing process.
Dye uptake is dependent on many factors. The result of unplanned variations in the conditions of operation during any step of the manufacturing chain may not become apparent until the fabric is dyed. Variations in temperature during the texturising of synthetic fibres, or irregular changes of tension during weaving, can lead to the development of either darker or lighter stripes after dyeing, wherever the affected yarns are incorporated into the fabric. Freedom from manufacturing faults and adequate resistance to the various treatments likely to be received by the goods during use are important to a consumer. Intensive efforts are therefore made to ensure that the coloration of fabric and yarn conforms to well-defined specifications. Commercial success in the modern coloration industry depends upon technical efficiency at all levels of activity, and this requires an appreciation of the properties of dyes and fibres, the way in which both behave during use and the objective manner in which the results of coloration processes are represented.
Origins of textile dyeing
The origins of dyeing are uncertain, but it is believed that coloured fabrics found in the ancient tombs of Egypt were in existence before 2500 BC. It is likely that the ancient art of dyeing originally spread westwards from India, and it may well have been accidental staining from berries and fruit juices that initially stimulated its development.
The use of colouring materials from plants (using roots, stems, leaves, flowers, fruit, seeds and lichens) and from the animal kingdom (using insects and shellfish) continued until the latter part of the nineteenth century. During the Middle Ages relatively few dyes were available, and European dyers imported their dyes from the Middle and Far East. During the fifteenth and sixteenth centuries their sources extended to the Americas with the discovery there of previously unknown natural dyes. It was during this period, when Spain and Portugal became prominent in the art of dyeing, that the Portuguese discovered a tree in South America from which a very desirable red dye could be extracted. In fact the tree was also known to the inhabitants of the Anderman Islands in the thirteenth century as ‘sappan’, but in its South American location it was called ‘brazil’. For this reason the Portuguese called the area in which it was found Terra de Brazil, and thus the name of the country was derived from the dye rather than the other way around.
The colour range of the natural dyes could be expanded to a limited extent by treating the fabric or yarn with metal salts (mordanting). Some of the results obtained on wool are illustrated in Plate 1 . Even so the only blue dye of the time was indigo, extracted either from the indigo plant (Indigofera sp.) or from woad (a different species of plant which gave a colour of less satisfactory performance), and greatly valued because of its excellent fastness to light.
Some form of quality appraisal existed even in ancient times. For example, the use of the dye Tyrian purple, with its high resistance to daylight, was restricted to the garments of those in authority. Tyrian purple was extracted from shellfish in the eastern Mediterranean, and was the most highly prized and expensive dye of classical times, being used for the robes of the kings of Medea and the royal houses of Persia, Babylon and Syria, as well as for the togas of Roman emperors. It ranked alongside indigo as one of the few natural dyes with resistance to fading. The high cost of this dye in ancient times is indicated by the quantity of sea snails required to provide sufficient extract for the purposes of dyeing. The efforts of Friedlander may be quoted as an example. During his elucidation of the chemical structure of the colour, he needed 12 000 of the creatures to obtain just 1.4 g of the dye!
Nowadays, when care of the environment is a major issue, it is tempting to assume that the use of natural colours is an environmentally friendly alternative to present-day practice. Unfortunately such assumptions change to doubts after the imagination has been stimulated by the details in Figure 1.1, which shows a description of the application of the once widely used Turkey red dye, obtained from the roots of the madder plant.
Indigo was the only natural dye to yield blue shades; its fastness to light was outstanding when compared with other natural dyes. As a result it achieved particular importance. Even so, the bacterial fermentation process used for its extraction from either Indigofera or woad plants was highly unpleasant and prompted Queen Elizabeth I to order the curtailment of the production of woad.
Compared with the extensive lists of dyes in today’s Colour Index, the colorants in use up to the nineteenth century were few in number. The more important ones are listed in Table 1.1. The last natural dye to be used commercially was logwood, which remained in use until the 1940s.