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Chemistry creates
colors to dye for

As far back as there are archaeological records, people used various techniques to add color to fiber as they made fabric for clothing, dyeing leather and wood for crafts, and to paint their bodies, while searching for new technologies to increase the range of colors and materials that can be dyed.

The earliest written record of the use of dyes dates back to 2600 B.C. in China.

Alexander the Great found purple robes nearly 200 years old in the royal treasury when he conquered Persia in 331 B.C. Purple garments remained the province of the rich until the 20th century, when the first synthetic purple was developed in England.

The purple dye used in ancient religious and royal robes came from one of several types of shellfish, mostly a mollusk known as Murex, that live in the shallow reefs of the Mediterranean. This Tyrian purple dye is of great value since the shells are not only rare, but the dye is also costly to produce. Only a few drops of the liquid used to make the dye can be arduously extracted from each shellfish.

To dye 10 pounds of wool required more than three pounds of the Murex secretions. According to one recipe, it took 12,000 mollusks to produce just enough to dye a single dress the size of a Roman toga. It is no wonder purple was the color of royal robes and that purple garments labeled the wearer as a wealthy or privileged individual.

Indigo dye made from plants has been used since Neolithic times in Europe and was valuable for being color-fast and unaffected by light.

In 55 B.C., Roman soldiers found "picti" (painted people) in France using woad, a relative of broccoli and mustard to dye themselves blue. The blue pigment derived from woad, known as Indican, is also present in the tropical indigo plant, from which the color gets its name. The Romans used both plants to make indigo dyes, and by the beginning of the common era were using madder, a relative of coffee and gardenia, for red dyes.

A purple dye called "murexide" was produced in a German laboratory in 1776 by treating uric acid with nitric acid and then with ammonia.

Nearly half a century later, William Prout, a British physician, analyzed and further refined the process, and suggested that the chemical, which he named "ammonium purpurate," might be useful commercially as a purple dye for wool, but the scarcity and expense of materials hindered the widespread appeal of the product.

In 1841, alizarin, the red dye made from madder since Roman times, was found to be derivative of anthracene, a cyclic hydrocarbon derived from coal tar. A commercial method of processing anthracene into alizarin went into production in 1868, and it became one of the early products of the German dyestuffs industry.

Like many great discoveries, the first truly synthetic dye arose from the combination of a chance chemical accident and a prepared, critical mind.

In 1856 at the Royal College of Chemistry in London, 17-year-old Henry William Perkin was trying to make fever-reducing quinine from aniline, like anthracene a cyclic hydrocarbon derived from coal tar. He failed to make quinine, but instead created a black substance from which he obtained a violet liquid never before seen. He immediately saw the potential of the new substance as a dye and found that it wonderfully dyed silk. He chose the name "mauveine" because it reminded him of the mauve color of mallow blossoms.

The next year, against the advice of his chemistry teacher (August Hofmann, who discovered several organic dyes including fuchsine, rosaniline, and aniline blue), Perkin set up a factory, bankrolled by his father on the banks of the Grand Union Canal not far from London. There he developed and commercialized the processes to produce and use the new mauveine dye, which is also called aniline purple.

The discovery of aniline purple set off a furious race to find more dyes with similar compositions, using aniline as a starting point. It also was a major step in the quest to understand molecular structures, which is at the heart of the chemical and pharmaceutical industries today.

In one of the world's first chemistry "R&D" laboratories, Perkin discovered two new dyes, Britannia violet and Perkin's green. So prolific was the factory's output that the water in the canal turned a different color every week, depending on what dyes were being made at the time.

Since then, dye researchers have discovered more categories of chemical compounds, more fields of application and mastered many challenges in synthesizing dyes of similar composition to those in natural products such as the red to blue colors in fruits and vegetables such as grapes, strawberries, apples and red cabbage. As dye technology grew, chemists improved synthetic dyes for natural fibers such as wool, silk and cotton and later for more difficult-to-dye synthetic fibers such as nylon, acrylic and polyester.

Today we can produce a dye of any desired color because of our ever-deepening understanding of how chemical bonds in molecules of different shapes and structures interact with light.

The challenge of modern dye chemistry is that today's dyes have to be nonfading, washable, affordable, capable of being processed easily and swiftly, and environmentally clean to prevent the obviously undesirable coloration of surface water by Perkin's first factory 150 years ago.

The complexity is magnified even further when consideration must also be given to the creation of colors that undergo minimal shift under different light sources.

It involves understanding not only the chemistry of the dyes and the dyeing processes, but also the specifics of laboratory synthesis, chemical engineering design to scale the laboratory techniques to the factory, and deep understanding of the interaction of light with various molecules at the quantum level.

All of this so we can enrich our lives by adding color to our artificial environments in the form of paint, food colors, clothing and other fabrics, makeup, hair color, printing inks and all of the other colors we enjoy that nature never thought of.