Question

 Classify dyes on the basis of application.

Answer 1

Hint: By definition dyes will be said to be coloured, ionizing and aromatic organic compounds which shows an affinity towards the substrate to which it's being applied. it's generally applied in an exceedingly solution that's aqueous. Dyes may additionally require a mordant to higher the fastness of the dye on the fabric on which it's applied.

Complete answer:
On the basis of application there are following varieties of dyes:
1. REACTIVE DYES
Reactive dyes are the foremost recent of dyes. These are the foremost popular within the world among fibre and fabric artists, used initially only by surface designers, but recently by weavers yet. There are now reactive dyes for a good range of fibres, e.g. cotton (PROCION), silk and wool (PROCINAL). The dye actually reacts with the fibre molecules to create colour and is, as a result, extremely fast to both light and washing. There are hot and cold-water reactive dyes, after all there's a dye for pretty much every need. they'll be most successfully used for silk painting, with a far better colour fastness than the standard basic dyes, and are already employed by batik artists. We will identify a reactive dye by the alkali wanting to depart the fixation process, which needs time to require place (silk and wool reactive uses acetic acid).

2. ACID DYES
Acid dyes are intended to be used on protein fibres but will be used on nylon and acrylics. they need a good light fastness but poor wash fastness

3. PRE METALLIZED DYES
These are acid dyes with the addition of 1 or two molecules of chromium.

4. DIRECT DYES
These substantive dyes colour cellulose fibres directly in an exceedingly hot dye bath without a mordant, to grant bright colours. they're not in no time to light or to wash. Direct dyes are generally any dyes which use salt as their only fixative.

5. AZOIC (NAPHTHOL) DYES
These are another variety of dye, but ones that are extremely fast to wash, bleach and light-weight. they're intended for cellulose fibres and might be used successfully on protein fibres, although the colours are different. These dyes are widely used everywhere Asia and Australia for batik and direct application. They'll be accustomed to give interesting texture colour effects on fabric, thread or paper. Their use for straight silk painting is minimal thanks to the issue in achieving evenness of painted colour.

6. DISPERSE DYES
Originally developed for acetate fibres, these are now the main dyes for synthetics. they're not soluble in water, but within the actual fibres themselves. They require a carrier to swell the fibres in order that the finely ground particles can penetrate. they're dyed hot, like direct dyes, but don't use salt. Disperse dyes are widely used for warmth transfer printing (Polysol). Dye is printed or painted onto paper and warmth pressed onto fabric. Prints have excellent light and wash fastness and robust bright colours. Their major disadvantage is that only synthetic fabrics are used.

7. VAT DYES
Vat dyes are the fastest for cellulose fibres. The dye is formed soluble with alkali, put in an exceedingly 'vat' with a chemical agent, usually sodium hydrosulphite, which removes all oxygen from the liquid, and also the fabric is dyed, then oxidized within the air to realize actuality colour. Synthetic indigo may be a characteristic dye, but there are many colours available

8. BASIC DYES
The colours are very bright, but not in no time to light, washing, perspiration. Fastness is improved if they're given an after-treatment or steaming, e.g. French Silk dyes are basic dyes and may be steamed to mend.

Note: The dyes were obtained from animal, vegetable or mineral origin with no or little processing. far and away the best source of dyes has been from the Plantae, notably roots, berries, bark, leaves and wood, but only some have ever been used on an advert scale.