ABSTRACT
In the late fifteenth century, the Portuguese explorer Vasco da Gama discovered a sea route to India. This led to the establishment of direct trade with India, China, and Japan. Importers could now avoid the heavy duties imposed by Persian and Greek middlemen and the lengthy and dangerous land routes which had previously been used. Consequently, the importation and use of indigo in Europe rose significantly. Much European indigo from Asia arrived through ports in Portugal, the Netherlands, and England. Spain imported the dye from its colonies in South America. Many indigo plantations were established by European powers in tropical climates; it was a major crop
in Jamaica and South Carolina. Indigo plantations also thrived in the Virgin Islands. However, France and Germany outlawed imported indigo in the 1500s to protect the local woad dye industry. Indigo was the foundation of centuriesold textile traditions throughout West Africa. The use of indigo here pre-dated synthetics. From the Tuareg nomads of the Sahara to Cameroon, clothes dyed with indigo signified wealth. Women dyed the cloth in most areas, with the Yoruba of Nigeria and the Manding of Mali particularly well known for their expertise. Among the Hausa male dyers working at communal dye pits were the basis of the wealth of the ancient city of Kano, and can still be seen plying their trade today at the same pits. In Mesopotamia, a neo-Babylonian cuneiform tablet of the seventh century BC gives a recipe for the dyeing of wool, where lapis-colored wool (uqnatu) is produced by repeated immersion and airing of the cloth. Indigo was most probably imported from India. The Romans used indigo as a pigment for painting and for medicinal and cosmetic purposes. It was a luxury item imported to the Mediterranean from India by Arab merchants. In Japan, indigo became especially important in the Edo period, when it was forbidden to use silk, so the Japanese began to import and plant cotton. It was difficult to dye the cotton fiber except with indigo. Even today indigo is very much appreciated as a color for the summer Kimono Yukata, as this traditional clothing recalls Nature and the blue sea. In North America indigo was introduced into colonial South Carolina by Eliza Lucas Pinckney, where it became the colony’s second-most important cash crop (after rice). When Benjamin Franklin sailed to France in November 1776 to enlist France’s support for the American Revolutionary War, 35 barrels of indigo were on board the Reprisal, the sale of which would help fund the war effort. In colonial North America, three commercially important species are found: the native I. caroliniana, and the introduced I. tinctoria and I. suffruticosa. Newton used “indigo” to describe one of the two new primary colors he added to the five he had originally named, in his revised account of the rainbow in Lectiones Opticae of 1675. Because of its high value as a trading commodity, indigo was often referred to as blue gold. Indigo is a vat dye that is one of the oldest classes of dyes known. Until the late 19th century indigo was obtained from plants, the most significant geing Indigofera tinctoria. Experience, patience and sensitivity for subtle color changes are necessary for successful dyeing. Obtain the darkest blues through a properly reduced vat and repeated dyeing to build color depth. Synthetic Indigo requires a reducing agent, Thiox, and an alkali, Lye. When the fabric is removed from the yellow-green dye vat and begins to oxidize, the
subtle changes from yellow-green through blue are captivating. In 1865 the German chemist Johann Friedrich Wilhelm Adolf von Baeyer began working with indigo. His work culminated in the first synthesis of indigo in 1880 from o-nitrobenzaldehyde and acetone upon addition of dilute sodium hydroxide, barium hydroxide, or ammonia and the announcement of its chemical structure three years later. BASF developed a commercially feasible manufacturing process that was in use by 1897, and by 1913 natural indigo had been almost entirely replaced by synthetic indigo. In 2002, 17,000 tons of synthetic indigo were produced worldwide. The primary use for indigo is as a dye for cotton yarn, which is mainly for the production of denim cloth for blue jeans. On average, a pair of blue jean trousers requires 3-12 g of indigo. Small amounts are used for dyeing wool and silk. Indigo carmine, or indigotine, is an indigo derivative which is also used as a colorant. About 20 million kg are produced annually, again mainly for blue jeans. It is also used as a food colorant, and is listed in the United States as FD&C Blue No. 2. (1) Natural Indigo – A variety of plants have provided indigo throughout history, but most natural indigo was obtained from those in the genus Indigofera, which are native to the tropics. The primary commercial indigo species in Asia was true indigo (Indigofera tinctoria, also known as I. sumatrana). A common alternative used in the relatively colder subtropical locations such as Japan’s Ryukyu Islands and Taiwan is Strobilanthes cusia. In Central and South America, the two species grown are I. suffruticosa (añil) and dyer’s knotweed (Polygonum tinctorum), although the Indigofera species yield more dye. Indigo dye is an important dyestuff with a unique shade of blue color. The natural dye comes from several species of plant. The dye gives a brilliant and eye-catching blue color to the fabric. This color partially penetrates the fabric but then also imparts surface blue color to the fabric. The word indigo is derived from the Latin Indicum and the Greek indikon meaning ‘blue dye from India’ or being more specific-’Indian substance’. Natural Indigo is the oldest known dye to mankind. When the synthetic substitute of the dye was not invented, all blue textiles were used to be dyed with indigo. These included the blue serge uniforms worn by the British police force and hospital staff, as well as military personnel and workman’s clothes worn by millions of people, inspiring the term ‘blue-collar worker’. The natural production of indigo is extracted from the leaves from a variety of plant species including indigo, woad, and polygonum. Only the leaves are used since they contain the greatest concentration of the dye molecules.
