The Science of Colour

Where do colours come from?

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Humans have been discovering and creating colour pigments for 100,000 years, originally from sources like ochre, bones and vegetation. Since then, philosophers and scientists have developed a kaleidoscope of unusual theories explaining why we see colours. “Pythagoras thought they were associated with musical notes; Aristotle, with times of day; and Plato suggested that the basic colours of white, black, red and “radiant” were mixed by tears to create the spectrum we see,” says New Scientist’s Sumit Paul-Choudhury.

Actually, as Isaac Newton discovered in 1672, different objects absorb and reflect different wavelengths of light. A red object, like an apple, is really reflecting the “type” of light that cells in our eyes pick up and interpret as the colour red. There are plenty of colours we can’t see because our eyes aren’t capable of recognising them, like infrared and ultraviolet. In fact, even shrimps have better colour vision than us humans.

Scientists are still learning exciting new things about colour and how we see it, and some of the earliest colour scientists were also artists. Five hundred years ago, painters belonged to the same guilds or trading societies as doctors. This was because, despite their very different goals, their experiments with herbs and chemicals meant they often bumped into each other during trips to the local apothecary.

Making your own paint is a pretty complex process, requiring three main components. A pigment gives paint its colour, a solvent keeps the paint in a fluid state until the artist is finished, and a binding medium hardens to form a solid layer when the paint dries. Back when artists had no choice but to make their own paints, they had to know enough about chemistry to understand how these processes worked and which materials would combine to produce the right reactions.

Artists have used some pretty weird and wonderful things to create colour, from cow’s pee to poisonous lead. Searching for the ideal colour could be dangerous work, as was the case for cobalt: a brilliant shade of blue. Cobalt ore was so tricky to extract that German miners names it “kobold” or goblin ore. Similar in appearance to silver ore, miners would be “tricked” by cobalt into thinking they had discovered a fortune, leading to folk-beliefs associating this element with mischievous spirits. Kobolds went on to find fame as a devious reptilian race in the fantasy table-top role-playing game Dungeons and Dragons.

Cobalt’s beastly origins might be rooted in fairy-tale, but as gross as it may seem, lots of colour pigments have been made throughout history that really did find their origins in living creatures. Cochineal is a shade of vibrant red first produced during the reign of the Aztec Empire. The Aztecs were notoriously fond of human sacrifice, believing that they owed their gods a blood debt. Don’t worry, though: the gory red pigment they used to dye fabrics and create paints with may have been known as “cactus blood”, but it was actually made from crushed-up beetles. Sound gross? You may be surprised to learn that cochineal dye is still used today as a food dye by places like Starbucks.

Bugs aren’t the worst of it- ancient Romans created purple pigments by boiling snails in huge, foul-smelling vats. You won’t find snail-purple frappucinos on the menu today, but this method of creating pigment was widely used right up until the 1850s, when it was replaced thanks to a young chemist’s lucky mistake. William Henry Perkin created mauveine, the world’s first synthetic dye, from the sludgy mess left over from a failed attempt to create anti-malarial medication.

Mauveine was popularised by royal trend-setter Queen Victoria. British monarchs don’t exactly have a great track record when it comes to employing toxic chemicals in the pursuit of beauty, and handling mauveine has since been linked with certain types of cancer. Tasty cochineal bugs seem to be the exception, as a great many early pigments were also violently poisonous. Realgar orange, used in everything from ancient Egyptian hieroglyphics to Russian Orthodox Icons, is an incredibly toxic arsenic sulphide.

One of the strangest tales of poisonous pigments is that of verdigris: the green colour that coats the Statue of Liberty. In the Middle Ages, verdigris production was an occupation dominated by women. Despite being banned from entering “skilled” occupations, women oversaw and controlled an extremely lucrative trade in this strange green substance, produced by the atmospheric oxidisation of copper. Even stranger, although customers developed sickness and anaemia from contact with the pigment, the women who handled and sold it were uniquely unaffected. To this day, nobody is quite sure why.

The modern manufacture of paints and pigments remains a fascinating chemical process- although our favourite colours are now synthesised in a laboratory and, thanks to health & safety laws, are far less likely to kill us. As in Medieval days, artists and scientists continue to rub shoulders in the field of art restoration, where a combined knowledge of chemistry and art history is essential in the conservation of old paintings.

Artists’ experiments in the field of colour science have not always been successful, as is most famously the case for Leonardo Da Vinci’s The Last Supper, now kept alive by a constant stream of interventions, from cleaning and glazing to an elaborate system of “pollution and humidity filtration systems”. Even these restoration attempts have taken a characteristically scientific trial-and-error approach, with restorers altering or removing their predecessors’ attempts as more is learned about the field and its techniques.

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Controversy surrounds the numerous restorations of Da Vinci’s work, many of which were allegedly “botched”

Both artists and scientists are driven by an intense curiosity to discover and record the world around us. Without a working knowledge of chemistry, artists throughout most of human history would not have been able to capture the images of their imagination. Before the invention of photography just 178 years ago, scientists from all fields relied on a proficient grasp of artistic techniques to record the visual results of their observations. To this day, creative and scientific advances continue to produce dazzling visual feats, from chameleonic nail-polish to colour as a marketing tool. One thing’s for certain: the field of colour chemistry remains as vibrant as ever.

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