Penny le Couteur & Jay Burreson (29 page)

Cochineal was a dye of the New World, used by the Aztecs long before the arrival of the Spanish conquistador Hernán Cortés in 1519. Cortés introduced cochineal to Europe, but its source was kept secret until the eighteenth century, in order to protect the Spanish monopoly over this precious scarlet dye. Later, British soldiers became known as “redcoats” from their cochineal-dyed jackets. Contracts for English dyers to produce fabric in this distinctive color were still in place at the beginning of the twentieth century. Presumably this was another example of government support of the dye industry, as by then British colonies in the West Indies were major cochineal producers.

Cochineal, also called carmine, was expensive. It took about seventy thousand insect bodies to produce just one pound of the dye. The small dried cochineal beetles looked a little like grain; hence the name “scarlet grain” was often applied to the contents of the bags of raw material that were shipped from cactus plantations in tropical regions of Mexico, and Central and South America for extraction in Spain. Today the major producer of the dye is Peru, which makes about four hundred tons annually, around 85 percent of the world's production.

The Aztecs were not the only people to use insect extractions as dyes. Ancient Egyptians colored their clothes (and the women their lips) with red juice squeezed from the bodies of the kermes insect (
Coccus ilicis
). The red pigment from this beetle is mainly kermesic acid, a molecule extraordinarily similar to its New World counterpart of carminic acid from cochineal. But unlike carminic acid, kermesic acid never went into widespread use.

Although kermesic acid, cochineal, and Tyrian purple were derived from animals, plants supplied most of the starting materials for dyers. Blue from indigo and woad, and red from the madder plant were the standards. The third remaining primary color was a bright yellow-orange shade from the saffron crocus,
Crocus sativus.
Saffron is obtained from the stigmas of flowers, the part that catches pollen for the ovary. This crocus was native to the eastern Mediterranean and was used by the ancient Minoan civilization of Crete as early as 1900 B.C. It was also found extensively throughout the Middle East and was used in Roman times as a spice, a medicine, and a perfume as well as a dye.

Once widespread over Europe, saffron growing declined during the Industrial Revolution for two reasons. First, the three stigmas in each hand-picked blossom had to be individually removed. This was a very labor-intensive process, and laborers at this time had largely moved to the cities to work in factories. The second reason was chemical. Although saffron produced a beautiful brilliant shade, especially when applied to wool, the color was not particularly fast. When man-made dyes were developed, the once-large saffron industry faded away.

Saffron is still grown in Spain, where each flower is still hand-picked in the traditional way and at the traditional time, just after sunrise. The majority of the crop is now used for the flavoring and coloring of food in such traditional dishes as Spanish paella and French bouillabaise. Because of the way it is harvested, saffron is the most expensive spice in the world today; thirteen thousand stigmas are required to produce just one ounce.

The molecule responsible for the characteristic yellow-orange of saffron is known as
crocetin,
and its structure is reminiscent of the orange color of β-carotene, each having the same chain of seven alternating double bonds indicated, below, by the brackets.

Although the art of dyeing no doubt started as a cottage craft and indeed continues in this mode to some extent today, dyeing has been recorded as a commercial enterprise for thousands of years. An Egyptian papyrus from 236 B.C. has a description of dyers—“stinking of fish, with tired eyes and hands working unceasingly.” Dyers' guilds were well established in medieval times, and the industry flourished along with the woolen trade of northern Europe and silk production in Italy and France. Indigo, cultivated with slave labor, was an important export crop in parts of the southern United States during the eighteenth century. As cotton became an important commodity in England, so too were dyers' skills in great demand.

Beginning in the late 1700s synthetic dyes were created that changed the centuries-old practices of these artisans. The first of these man-made dyes was picric acid, the triply nitrated molecule that was used in munitions in World War I.

An example of a phenolic compound, it was first synthesized in 1771 and used as a dye for both wool and silk from about 1788. Although picric acid produced a wonderfully strong yellow hue, its drawback, like that of many nitrated compounds, was its explosive potential, something that dyers did not have to worry about with natural yellow dyes. Two other disadvantages were that picric acid had poor light fastness and that it was not easily obtained.

Synthetic alizarin became available in good quantity and quality in 1868; synthetic indigo became available in 1880. In addition, totally new man-made dyes were prepared; dyes that gave bright, clear shades, were colorfast, and produced consistent results. By 1856 eighteen-year-old William Henry Perkin had synthesized an artificial dye that radically changed the dye industry. Perkin was a student at London's Royal College of Chemistry; his father was a builder who had little time for the pursuit of chemistry because he felt it was unlikely to lead to a sound financial future. But Perkin proved his father wrong.

Over his Easter holidays of 1856, Perkin decided to try to synthesize the antimalarial drug quinine, using a tiny laboratory that he had set up in his home. His teacher, one August Hofmann, a German chemistry professor at the Royal College, was convinced that quinine could be synthesized from materials found in coal tar, the same oily residue that was, a few years later, to yield phenol for surgeon Joseph Lister. The structure of quinine was not known, but its antimalarial properties were making it in short supply and great demand. The British Empire and other European nations were expanding their colonies into malaria-ridden areas of tropical India, Africa, and Southeast Asia. The only known cure and preventive for malaria was quinine, obtained from the increasingly scarce bark of the South American cinchona tree.

A chemical synthesis of quinine would be a great achievement, but none of Perkin's experiments were successful. One of his trials did, however, produce a black substance that dissolved in ethanol to give a deep purple solution. When Perkin dropped a few strips of silk into his mixture, the fabric soaked up the color. He tested this dyed silk with hot water and with soap and found that it was colorfast. Perkin exposed the samples to light; the color did not fade—it remained a brilliant lavender purple. Aware that purple was a rare and costly shade in the dye industry and that a purple dye, colorfast on both cotton and silk, could be a commercially viable product, Perkin sent a sample of the dyed cloth to a leading dyeing company in Scotland. Back came a supportive reply: “If your discovery does not make the goods too expensive, it is decidedly one of the most valuable that has come out for a very long time.”

This was all the encouragement Perkin needed. He left the Royal College of Chemistry and, with financial help from his father, patented his discovery, set up a small factory to produce his dye in larger quantities and at a reasonable cost, and investigated the problems associated with dyeing wool and cotton as well as silk. By 1859
mauve,
as Perkin's purple was called, had taken the fashion world by storm. Mauve became the favorite color of Eugénie, empress of France, and the French court. Queen Victoria wore a mauve dress to the wedding of her daughter and to open the London Exhibition of 1862. With royal approval from Britain and France, the popularity of the color soared; the 1860s were often referred to as the mauve decade. Indeed, mauve was used for printing British postal stamps up until the late 1880s.

Perkin's discovery had far-reaching consequences. As the first true multistep synthesis of an organic compound, it was quickly followed by a number of similar processes leading to many different colored dyes from the coal tar residues of the coal gas industry. These are often known collectively as coal tar dyes or aniline dyes. By the end of the nineteenth century dyers had around two thousand synthetic colors in their repertoire. The chemical dye industry had effectively replaced the millennia-old enterprise of extracting dyes from natural sources.

While Perkin did not make money from the quinine molecule, he did make a vast fortune from
mauveine,
the name he gave to the molecule that produced the beautiful deep purple shade of mauve, and from his later discoveries of other dye molecules. He was the first person to show that the study of chemistry could be extremely profitable, no doubt necessitating a retraction of his father's original pessimistic opinion. Perkin's discovery also emphasized the importance of structural organic chemistry, the branch of chemistry that determines exactly how the various atoms in a molecule are connected. The chemical structures of the new dyes needed to be known, as well as the structures of the older natural dyes like alizarin and indigo.

Perkin's original experiment was based on incorrect chemical suppositions. At the time it had been determined that quinine had the chemical formula of C
₂₀
H
₂₄
N
₂
O
₂
, but little was known about the structure of the substance. Perkin also knew that another compound, allyltoluidine, had the chemical formula C
₁₀
H
₁₃
N, and it seemed to him possible that combining two molecules of allyltoluidine, in the presence of an oxidizing agent like potassium dichromate to supply extra oxygen, might just form quinine.