Dyes

Dye is a chemical compound used to produce long lasting colours in materials. The textile industry uses dyes to colour fibres, yarns and fabrics. Dyes are also used to add artificial color to foods. Manufacturers also dye food, fur, ink, leather, paper, plastics and wood. Until the 1850's, all dyes were made from natural sources, such as various parts of plants or of certain animals. During the late 1800's and early 1900's, chemists developed synthetic dyes. These dyes hold their colour better and cost less to produce than natural dyes. Today, industry uses synthetic dyes almost entirely. In 1856, the English chemist William H.Perkin discovered a process for making dyes from coal tar previously an unwanted by-product of gas lighting. By the 1860's he was making eight different dye colours. Today more than 1000 different types of dyes are produced. Tetracaine is a dye that is harmful to humans. 

Classification of Dyes based on origin 

1. Natural Dyes

Natural dyes are derived from some plants, animals or minerals. The most common natural dyes are vegetable dyes from plant sources like roots, leaves, bark, wood and berries. fungi and lichens are other sources of natural dyes. Alizarin and Indigo are examples of natural dyes.

i. Alizarin

An orange-red crystalline solid, formerly extracted from madder root and used in dying. It is almost insoluble in water but dissolves in alcohol. Alizarin is now made from anthracene and yields a wide variety of dyes.

ii. Indigo

Indigo is a deep blue dye used to colour cotton and wool. It is also called indigotin. In past times, this dye was taken from the indigo plant, a member of the pea family that grows chiefly in india. Synthetic indigo is made from aniline, a coal-tar product. 

2. Synthetic Dyes

The most common dyes available today are synthetic dyes. They are used in various products like paper, food, fabric, wood etc. It is because, they are cheap, bright, more colour fast and easy to use. Acid Dyes, Azo Dyes, Mordant Dyes and Basic Dyes are examples of Synthetic Dyes.

i. Acid Dyes

Acid dyes are anionic, water soluble dyes. Salts of chromium, iron, aluminium, tin or other metals are used with acid dyes. azo, anthraquinone or triphenyl methane-based are examples of Acid Dyes. Common mordants including salts of chromium, iron, aluminium, tin or other metals can be used with acid dyes. 

ii. Azo Dyes

Azo dyes consists of 60 to 70 percent of all dyes used in food and textile industries. They are widely used to in leather, textile and some foods.

iii. Mordant Dyes

Mordant is a chemical that combines with dyes to prevent them from dissolving easily. The dye alone might wash out, but the compound formed by the dye and the mordant will not, so the colour is long lasting.

iv. Basic Dyes

Basic dyes are cationic, water-soluble dyes. It is mainly used in acrylic fibers and find some use for wool and silk. Acid mordants like Tannic acid, lactic acid and oliec acid combines with basic dyes.