PREVIOUS YEAR QUESTIONS | FOOD SCIENCE & NUTRITION | L-21|

Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used. Dyeing and printing are different applications; in printing, color is applied to a localized area with desired patterns. In dyeing, it is applied to the entire textile.

The primary source of dye, historically, has been nature, with the dyes being extracted from animals or plants. Since the mid-19th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process, from loose fibers through yarn and cloth to complete garments.

Acrylic fibers are dyed with basic dyes, while nylon and protein fibers such as wool and silk are dyed with acid dyes, and polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.

Etymology

The word ‘dye’  comes from the Middle English ‘deie’, and from the Old English ‘dag’ and ‘dah’. The first known use of the word ‘dye’ was before the 12th century.

History

Children playing amongst drying colored cloth in Bangladesh

The earliest dyed flax fibers have been found in a prehistoric cave in the Georgia and dates back to 34,000 BC. More evidence of textile dyeing dates back to the Neolithic period at the large Neolithic settlement at Çatalhöyük in southern Anatolia, where traces of red dyes, possibly from ocher, an iron oxide pigment derived from clay, were found. In China, dyeing with plants, barks, and insects has been traced back more than 5,000 years.  Early evidence of dyeing comes from Sindh province in Pakistan, where a piece of cotton dyed with a vegetable dye was recovered from the archaeological site at Mohenjo-daro (3rd millennium BCE). The dye used in this case was madder, which, along with other dyes such as indigo, was introduced to other regions through trade. Natural insect dyes such as Cochineal and kermes and plant-based dyes such as woad, indigo and madder were important elements of the economies of Asia and Europe until the discovery of man-made synthetic dyes in the mid-19th century. The first synthetic dye was William Perkin’s mauveine in 1856, derived from coal tar. Alizarin, the red dye present in madder, was the first natural pigment to be duplicated synthetically in 1869, a development which led to the collapse of the market for naturally grown madder.The development of new, strongly colored synthetic dyes followed quickly, and by the 1870s commercial dyeing with natural dyestuffs was disappearing. An important characteristic was light-fastness – resistance to fading when exposed to sunlight using industrial techniques such as those developed by James Morton.