A variety of natural dyes are obtained from different plants parts viz., roots, bark, leaf, fruit, bark, seed, flower etc., that produce varied colours such as red, yellow, blue etc. [1] . Of the total 2000 plant pigments known so far worldwide, only 150 have been commercially exploited. In Indian context, 50 of the total 450 dye yielding plants are considered to be very important [1] . On the basis of colours, natural dyes can be classified as Red dyes, yellow dyes, blue dyes and black dyes. Red colour dyes (e.g. Madder) are mostly extracted from roots or barks of plants and are usually based on anthraquinone and its derivatives (Figure 1). These dyes are stable to light and washing.

Yellow colour dyes are the most common colour found in nature and majority (ca. 90%) are flavonoids. They are known to produce pale shades, less light fastness and fairly good wash fastness e.g., tesu, turmeric, kapila (Figure 2). Blue

colour dyes (e.g., indigo) gives excellent fastness to light and washing (Figure 3). Black shades are usually derived from tannin rich plant dyes and are fairly substantive towards cellulosic and protein fibre with good overall fastness properties, for example, Logwood, Harda etc. In this study, a variety of natural dyes were evaluated for obtaining a spectrum of colours such as red colour from red sandel wood; Orange from Madder; Yellow from Safflower, Turmeric, Berberris and Harda; Blue from Indigo; Green from a combination of Indigo and Berberris; Violet from Alkanet; Brown-green from Basil, Eucalyptus, Heena and Hibiscus (Table 1; Figures 1-7).

The efficiency of extraction of coloured components present in plants depends on medium of extraction (aqueous or solvent or acids/alkali), pH of the Medium (acidic/alkali/neutral) and conditions of extraction (temperature, time, material- to-liquor ratio and particle size of the substrate). Optimum conditions of extraction variables are determined through extracting the natural colour component from source material by varying extraction parameters of liquor and measuring the optical density of corresponding coloured liquor by using spectrophotometer.

Also, the gravimetric yield of colour can be measured by filtering the extraction liquor through standard filtration process followed by evaporation of solvent, washing and finally drying to get the purified natural colour. In addition, it is important to note that the amount of dye present in plant varies greatly depending on the season, age of the plants, and some other factors. Natural dyes extracted in three different pH mediums (acidic, neutral and alkaline) have been tested for their dyeing potential using different mordanting techniques and three different mordants. It was observed that for most of the plant dyes extraction was better with alkaline medium.

A dye comprises of two principal groups: the chromophore and auxochromes. Chromophore (usually an aromatic ring) is associated with the colouring property and has unsaturated bonds, whose numbers decides the intensity of colour. The auxochrome helps the dye molecule to combine with the substrate, thus imparting colour to the latter. Although some fabrics such as silk and wool can be colored simply by dipping in the dye, others such as cotton require a mordant. Some natural dyes, such as indigo will give good color when used alone;

these dyes are called direct dyes or substantive dyes. The majority of plant dyes, however, require a mordant or a chemical used to “fix” the color to the textile fabric, and prevent the color from either fading with exposure to light or washing out. These dyes are called adjective dyes such as logwood. By using different mordants, dyers can often obtain a variety of colors and shades from the same dye. Fibers or cloth may be pre-treated with mordants, or the mordant may be incorporated in the dye bath. Mordants can be broadly classified into three types: Metallic mordants (Metal salts of iron, copper aluminium etc.); Tannins (Myrobalan and Sumach); Oil Mordants (mainly used in dyeing Turkey red colour from Madder). The final colour, lustre and colour fastness properties of the dyed fabric are dependant not only on the dye but are also determined by the concentration and type of mordants used. Thus, a mordant is more important than the dye itself. Thus, an ideal mordant will be the one that produce required colour yield at low cost without affecting the physical properties of fabric. It should not cause any noxious effect during processing and the dyed textile material should not have any carcinogenic effect during use. Common mordants are alum (usually used with cream of tartar, which helps evenness and brightens slightly); iron (or copper) (which saddens or darken colors, bringing out green shades); tin (usually used with cream of tartar, which blooms or brightens colors,

especially reds, oranges and yellows), and blue vitriol (which saddens colors and brings out greens shades). In present study, it was observed that alum does not alter the colour of original dye; Copper sulphate elevates the colour and gives greenish hue to the fabric and ferrous sulphate adds blackish hue to the colour and gives the shades of grey and black making colour dark and dull.

Different types of mordant and method of mordanting significantly affect the rate and extent of photo fading. For example, Copper or ferrous sulphate gives high resistance to fading, whereas stannous chloride does not. In comparison, light fastness improves when post-mordanting is conducted with copper or ferrous ion but pre-mordanting is superior in case of stannous chloride or alum [10] . Synergistic effect of mordant is generally observed while using binary combinations of mordants. It has been reported that the combinations of harda and aluminium sulphate as double mordants are best suited for jute fabric for red sandal wood natural dye [11] . Various kinds of shades like black to brown and green to yellow to orange can be obtained by application of varied mordants [4] . Mordants form metal complexes between fabric and dye. On application of mordant, the metal salts anchoring to the fibres, attracts the dye/organic pigment molecules to be anchored to the fibres and finally creates the bridging link between the dye molecules and the fibre by forming coordinating complexes.

pH of the dyeing bath can be alkaline, acidic or neutral. There are various reports available on different methods of mordanting on different fibers such as cellulosic, protenic and synthetic for dyeing with different natural dyes. Dyeing of cotton and silk with babool, tesu, manjistha, heena, indigo, marigold etc is reported [12] [13] [14] [15] . Depending upon the fabric to be dyed, the different parameters of the dyeing bath are modified to get the desired results. Besides the conventional method of dyeing in a dye bath at a specific temperature in the presence of suitable mordants, newer technologies have also been tested these days. These technologies include use of nanoparticles, ultrasonics energized dyeing, use of supercritical carbon dioxide (scCO₂) as a fluid medium [4] .

The resistance of a material to change its colour or extent of transfer of its colours to adjacent white materials in touch is referred to as colour fastness. For any textile, it is measured with respect to degree of loss of colour or in terms of a staining scale i.e. the extent to which the colour is passed on to the accompanying white material. Generally, light fastness, wash fastness and rub fastness are measured for testing the efficacy of dyeing of textiles. Light fastness of most natural dyes particularly those derived from flower petals are found to be poor-medium. Yellow dyes showed poor light fastness; reds showed better light fastness followed by blue and black. However, the use of mordants has shown to improve the fastness properties. The pH of washing medium plays a very important role in improving the wash fastness of textiles dyed with natural dyes. Generally, natural dyes show moderate wash fastness. Logwood and indigo dyes showed better wash fastness. Majority of natural dyes exhibited moderate to good rub fastness and does not require any after-treatment.