Dyes – natural and synthetic dyes. The importance of science in dyes.
Dyes are substances that impart colour to a material. The term colorant is often used for dyes (also called dyestuffs). Dyes are usually soluble—or can be made to be soluble—in water. Once a dye is dissolved in water, the material to be dyed can be absorbed in the dye solution. As the material soaks up the dye and dries, it develops a colour. If the material then retains that colour after being washed, the dye is said to be colourfast. Dyes can be obtained from natural sources, such as plants, animals, and minerals or can be synthetic dyes, i.e. manmade by humans.
Humans have used natural dyes for thousands of years. Red iron oxide, for example, has long been used to colour cloth and pottery and to decorate the human body. Red dirt imparts a brilliant orangish-red colour to cloth that is almost impossible to wash out. Other natural dyes include sepia, obtained from cuttlefish, and Indian yellow, obtained from the urine of cows that have been force-fed mango leaves. One of the most popular natural dyes still in use today is carmine, which is obtained from the cochineal beetle.
Cochineal is a traditional natural dye for colouring textiles especially in South and Central America and has been used for beautiful, lightfast and permanent scarlets, pinks and reds for centuries. This natural dye is derived from the cochineal beetle. Cochineal appears to have been used in Peru for about 1500 years and in Mexico for 1200 years. Mexican cochineal was one of the main exports of the Spanish empire from the New World and as important as gold or silver. Red was an expensive colour to produce in medieval times and red clothes were an important status symbol, with the result that red dyes commanded high price. As cochineal produces a deep long lasting red, the cochineal red dye was very highly valued. In the nineteenth century, when artificial dyes were developed, the production of...