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Parshat Shelach — The color purple

One chemist's experiments changed science and led to the rediscovery of biblical blue, which had been lost for hundreds of years (Shelach)
A sample of silk dyed mauve. (CC BY-SA, Rzepa/ Wikimedia Commons)
A sample of silk dyed mauve. (CC BY-SA, Rzepa/ Wikimedia Commons)

In 1856, William Perkin made a serendipitous discovery that would forever change the world. He had been studying at the Royal College of Chemistry (now part of Imperial College) for three years. Over the Easter vacation his professor August Wilhelm von Hofmann told him to try and use aniline — a chemical derived from coal tar — to synthesize quinine, which is used to treat for malaria.

Perkin had built a small laboratory above his London home. While trying to produce quinine, he noticed that when he mixed alcohol with the sludge left at the bottom of the flask it produced an intense purple color.

Since he was also interested in art and photography, Perkin realized that the purple dye he had accidentally produced was different and better than any colors available at that time.

Along with his friend Arthur Church and his brother Thomas, Perkin carried out further trials and worked out how to scale up production of the new color. Since he had developed it outside of his school work and it was unrelated to synthetic quinine, he was able to patent the method for producing the new color which he named mauveine, though originally he wanted to call it Tyrian Purple. At the time he was only 18 years old.

Using money from his father, he and his brothers built a factory and mass produced mauviene. Not only was the discovery serendipitous, but the timing was perfect. He needed coal tar to make his dye, and Britain was at the height of the Industrial Revolution, using coal gas and coke which made lots and lots of coal tar (which had been considered basically a waste product until that time).

William Henry Perkin, scanned from F. J. Moore’s 1918 book, “A History of Chemistry.” (Public Domain/ Wikimedia Commons)

At first Perkin struggled to get dyers to use his new color, but once Queen Victoria wore a mauveine-colored dress, the country went crazy for it.

Perkin continued to develop more colors from aniline, including aniline red (in 1859), aniline black (in 1863) and alkalate magenta (1864) along with Britannia Violet and Perkins’ Green in the late 1860s. In 1869 he worked out how to commercially produce a red dye named alizarin. However, the German company BASF independently discovered the same method and filed a patent one day before Perkin.

The colors discovered by Perkin had so many uses — from blue-rinse hair dye to giving hotdogs their pink color.

Although Perkin’s colors were pretty and changed the way people dressed, their importance went far beyond fashion. Many of his colors are now used in medical research to stain microbes and bacteria which were previously invisible, leading researchers to identify tuberculosis, cholera and anthrax, among others.

Almost single-handedly, Perkin turned chemistry in Britain from a hobby along the lines of alchemy into a full-fledged science.

“The first public laboratory I worked in was the Royal College of Chemistry in Oxford Street, London, in 1853-1856,” Perkin reminisced in 1906, 50 years after his discovery of mauveine. “There were no Bunsen burners — we had short lengths of iron tube covered with wire gauze.”

Blue Plaque erected by Stepney Historical Trust at Gosling House, Cable Street London E1 0DR. (CC BY-SA, Spudgun67/ Wikimedia Commons)

Very few high schools and even fewer universities taught chemistry. According to Simon Garfield, Perkin’s father, though supportive, had hoped his son would become an architect, rather than mess around with chemicals.

Perkin’s discovery of the usefulness of coal-tar led to many new fields of investigation into the properties of this by-product of the industrial age. Coal-tar has since given us such diverse products as analgesics and saccharine.

In 1874 Perkin sold his factory and retired. From then on he dedicated himself to scientific research. He created synthetic perfumes and fragrances and won a Davy Medal from the Royal Society for his scientific work.

At a dinner in Perkin’s honor, held in Boston to mark the 50th anniversary of his discovery, Dr Hugo Schweitzer spoke (and subsequently published his speech in the journal Science).

It is hard to realise today what an epoch-making idea it was at the time to dye fabrics with a substance evolved in the laboratory and having no relation whatever to the dyestuffs then known. It was truly a spark of genius which led perkin to investigate the dyeing properties of that dark-colored precipitate which would have been cast away by any other scientist of that period and particularly by his master, Hofmann.

Today about 2,000 individual dyestuffs are known, giving the whole range of the colors of the rainbow, and complying with every demand of taste, fashion and stability. They surpass in beauty and brilliance the colors supplied by nature.

Schweitzer’s comment that the synthetic dyes were more brilliant than natural colorings also highlights another way in which Perkin impacted the world.

Foods and dishes colored with cochinilla. (CC BY-SA, De1234567890/ Wikimedia Commons)

While many of the earlier dyes came from plants, some of the natural colors were procured by killing huge numbers of animals.

For example, it takes about 80,000 to 100,000 dead cochineal insects to make one kilogram of the red dye named after them. Nowadays cochineal is still used for food coloring and in some lipsticks, but much less for fabrics.

Sepia brown is made from the ink sacs of octopus and cuttlefish. It has been entirely replaced by synthetic dyes, but was once used widely as ink. But it was extracted from the animals after they no longer had any use for it on account of being dead.

The original Tyrian Purple after which Perkin initially wanted to name his new color was made from various types of Murex brandaris marine snails. It takes some 10,000-12,000 Murex to produce a single gram of dye — which is barely enough to color the edge of a tunic. This made purple a very expensive color, which is one reason it was worn only by the aristocracy.

Photo of the shell of Hexaplex trunculus. (CC BY, Dezidor/ Wikimedia Commons)

Another snail used to produce dye was Hexaplex trunculus, often called Murex trunculus. In his 1913 doctoral thesis, Rabbi Yitzhak HaLevi Herzog (who went on to become the first Chief Rabbi of the State of Israel, and was the grandfather of the former politician and current head of the Jewish Agency Isaac Herzog) suggested that this may be the chilazon used to produce the Biblical color tekhelet mentioned in this week’s Torah portion as the color of the ritual fringes to be placed on the corner of garments.

Hexaplex trunculus is a species of carnivorous marine snail which attacks its prey in groups. It has a gland which contains a yellowish liquid which has been used for centuries to produce a purplish or indigo dye. Archeologists have found dye-producing “factories” in Tyre with mounds of these Hexaplex shells. Blue-dyed fabric from the 1st century has been chemically analyzed and found to have been produced from Hexaplex trunculus.

However, the dye Rabbi Herzog produced from the snail came out purple. And tekhelet must be blue. But, in the mid-1980s it was serendipitously discovered that if the dye was exposed to sunlight during the preparations it was consistently blue.

Tzitzit with tekhelet. (Public Domain, החבלן/ Wikimedia Commons)

It was ultimately due to Perkin’s chemistry that scientists had the tools and framework to rediscover bibilical tekhelet which is now commercially available for the first time in hundreds of years.

In the Talmud (Sota 17a), Rabbi Meir says that tekhelet is a reminder of the Heavenly Throne. God created the physical world for our benefit and we must acknowledge that with everything we see. But we should remember that human ingenuity also comes from God. The study of science along with an open and inquiring mind can show us even greater insight into the beauty of the world that God created.

About the Author
David Sedley lives in Jerusalem with his wife and children. He has been at various times a teacher, translator, author, community rabbi, journalist and video producer. Born and bred in New Zealand, he is usually a Grinch, except when the All Blacks win. And he also plays a loud razzberry-colored electric guitar.
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