**1. Introduction**

Love for colours is a natural instinct and every individual has his own choice and liking for colour. The icy appearance of Hamaliyan ranges or lush green forests or fields of agriculture or trees laden with colorful fruits or butterflies moving from flower to flower presents the beauty of nature, generation after generations are being attracted. The choice of beautiful fascinating colours reflects the aesthetic sense of humans that varies.

Colour is visual perceptual property corresponding in humans to the categories called red, yellow, blue and others. It is a sensation that arises from the activity of retina of the eye and its attached nervous mechanism, and results in a specific response to the radiate energy of certain wavelength and intensity. Thus it is a quality of an object with respect to light (Mizzarini *et al.*, 2002).Colorants may be either pigment or a dye which are characterized by their ability to absorb or emit light in the visible range 400-700nm.They may be organic or inorganic depending upon their structure and method of production.

Dyes are the coloured substances which are capable of imparting their colours to the matrix which may be fiber, paper or any object. They must have fixing tendency on a fabric that is impregnated with their solution and the coloured fixed dyes must be fast to light as well as resistant to action of water, dilute acids, alkalies, various organic solvents used in dry cleaning, soap solutions, detergent, etc ( Shukla, 1992 ) . A pigment generally is a substance which is insoluble in the medium in contrast to dye in which it is applied and has to be attached to a substrate by additional compounds e.g. polymer in paints and plastics (Taylor and Nonfiction, 2006)

A compound looks coloured because it has absorbed certain electromagnetic radiation from the visible region. The moieties, present in colouring substance, responsible for the absorption of electromagnetic radiation and reflect in the visible region are called chromophores (Younas, 2006).Ultraviolet radiation constitutes to 5% of the total incident sunlight on earth surface (visible light 50% and IR radiation 45%). Even though, its proportion is quite less, it has the highest quantum energy compared to other radiations. Light is electromagnetic in nature. Within the electromagnetic spectrum, human eye captures visible light in the range between about 380 nm and 700 nm (Mizzarini *et al.*, 2002). Dyes absorb electromagnetic radiation of varying wavelength in the visible range of

Effect of Radiation on Textile Dyeing 3

**Colours Chemical Classification Common Names** Yellow and Brown Flavone Dyes Quercitron, Tesu

Brown Naphthoquinone Dyes Henna , Alkanet Black Benzophyrone Dyes Cochineal , Madder

Neutrals Tannins Pomegranate, Eucalyptus

*Commercialization* of natural dyes can be done successfully by a systematic and scientific approach to extraction, purification and use. Optimization of extraction condition is a must to minimize the investment cost and to avoid discrepancy in the dye shade quality. Natural dyes occur in many plant parts in small quantities and as complex mixtures with many chemical compounds of similar or different structures. These compounds vary considerably with change in general, same genus but different species and ecological conditions of the plant source. So when natural dyes extracted from these sources are used for dyeing and printing, variation in shade, depth and tone, among others, may arise. Further, chemical components of plants change with age and maturity of the parts. Extraction may include drying, pounding, soaking, skimming, crystallizing, condensing, caking and liquidifying, among others, depending on the quality and species of the dye yielding plant, mineral and

*Synthetic dyes* are a class of highly coloured organic substances, primarily utilized tinting textiles that attach themselves through chemical bonding between the molecules of dye and that of fiber. The use of natural dyes in textiles was eliminated since synthetic dyes give variety of reproducible shades and colours (Deo and Desai, 1999). Synthetic dyes are classified on the basis of chemical structure or on the basis of methods of application to the material. Dyes are synthesized in many ways by using different chemicals. On the basis of

*Acid dyes:* These dyes are anionic and form ionic bonds with fibers that are cationic in acid solutions. These dyes are applied onto the acrylic, wool, nylon and nylon/cotton blends. These are called acidic because they are normally applied to nitrogenous fibers in inorganic

*Azoic dyes:* These dyes contain azo component (–N=N-), used for dyeing of cotton fabrics. In the dyeing process fiber is first treated with coupler followed by application of azo dye. This

*Basic dye*: These dyes are cationic and form ionic bonds with anionic fibers such as acrylic, cationic dyeable polyester and cationic dyeable nylon. These are amino derivatives used

*Disperse dyes:* These dyes are colloidal and are soluble in hydrophobic fibers. Mostly these dyes are used for coloring polyester, nylon, and acetate and triacetate fibers. They are

*Direct dyes:* These are also azo dyes applied generally on cotton-silk combination from neutral or slightly alkaline baths containing additional electrolyte. These dyes predominantly interact and attach themselves with the Matrix ( wool , polyamide fabric) through electrostatic

usually applied from a dye bath as dispersion by direct colloidal absorption method

interactions. These dyes are used to color cellulose, wool, nylon, silk etc.

Yellow Iso-quinoline Dyes Barberry Orange- Yellow Chromene Dyes Kamala

Blue Indigoid Dyes Logwood Red Anthraquinone Dyes Indigo

insect (Shrivastava and Dedhia, 2006; Vankar *et al.,* 2000).

methods of application dyes are categorized as:-

or organic acid solutions.

type of dye is extremely fast to light.

mainly used for application on paper

Table 1.

spectrum. Human eyes detect the visible radiations only for the respective complementary colours.

Fig.1 shows the different regions of spectrum with their wavelengths.

Fig. 1. Regions of electromagnetic spectrum
