Purple is a colour which is between red and blue. You can make it by mixing red and blue paint¹, or by mixing red and blue light in the correct proportions, but you won't find purple in the rainbow. It is not a pure colour with only one frequency of light – it can only ever exist as a mixture. The name 'purple' covers a number of different shades with various names such as mauve, maroon, lilac and even violet, although pure violet is a spectral (rainbow) colour, not a mixture of red and blue.

The name purple was originally applied to a different, much redder colour, but over time, people's opinions as to exactly what the word meant changed.

Phoenicia – the Land of Purple

The first purple was produced from a type of water snail – the Murex brandaris or spiny dye-murex, known in recent times as Haustellum brandaris. This snail produces a gooey secretion which when exposed to sunlight turns purple. This can be used for dyeing cloth and had the unique property in ancient times of being both a striking colour and colour-fast. It didn't come out in the wash but actually improved with washing.

These snails were common in the eastern Mediterranean and the Near East. We know from archaeological sites in Qatar that the locals made purple dye from crushing up vat loads of these snails as long ago as 1800 BC. By 1500 BC, the use of Murex for making purple dye was common throughout the Eastern Mediterranean, with mounds of crushed snail shells being found both in Crete and at Ugarit in Phoenicia (modern Lebanon). The purple dye industry really took off a few centuries later around another Phoenician city, Tyre (modern Tyr). It became the world centre of production of the purple dye, which became known as 'Tyrian Purple'. The name 'Phoenicia' is from an old Greek word meaning 'Land of Purple'. The people themselves called the country Canaan.

The best dye was made by extracting the organ that produced the dye from the snail rather than including the whole snail in the mix. This was a labour-intensive task. It took the organs from 250,000 snails to make an ounce² of dye, so it was extremely expensive.

Tyrian Purple was a much redder or browner colour than the purple we know today. It was described as the colour of clotted blood. It's hard to know exactly what colour it was, and the exact process the ancients used to make the dye is not known, but modern experiments with the snails suggest the colour looked something like this:

This is so red that most people nowadays would not consider it to be purple. Note that the exact shade of this depends on your display, so it is only an approximation.

According to the Roman historian Pliny, the best cloth was first dyed in Tyrian Purple, which was dark, and then dipped in a dye from another type of snail, the 'buccinum' (Thais haemastroma) to give it a crimson-like sheen.

Tyrian Purple was analysed in 1909 by chemist Paul Friedländer and discovered to be 6,6'-dibromoindigo, which has an interesting structure with two benzene rings, two pentagonal rings with a nitrogen atom in each, and a bromine atom at each end:

Dogs and Drunkards

In Greek mythology, it was the hero and demigod Heracles's dog that discovered the dye by chewing some of the snails. Heracles noticed the purple stains around the dog's mouth and worked out from this how to make the dye.

Amethysts are a semi-precious stone with a purple colour. The word 'amethyst' is Greek and means literally 'not drunk', as the ancients believed amethysts were a cure for intoxication, possibly due to the similarity of the colour to red wine.

Romans

The Greek name for the colour was πορφυρα, which in our alphabet is porphyra. This word came into Latin as purpura which obviously gave us our word 'purple'. The Romans were very fond of their purple. Because it was an expensive dye to produce, being 'worth its weight in silver', it became a sign of wealth and importance and was reserved for important people. Senators, quaestors and praetors were allowed to have a band of purple along the edge of their otherwise white togas as a sign of their status. Generals could wear all-purple clothes while triumphant generals could wear purple with a gold edge.

With the conversion of Rome from Republic to Empire, the colour was also worn by the Emperor himself, and eventually, by about 400 AD, was reserved for the sole use of the emperor. Because of this, the name 'Imperial Purple' is often used for the Tyrian Purple colour.

Byzantines

Centuries later, the Western Roman Empire was conquered by barbarians, but civilisation continued in the Eastern Roman Empire, which we refer to as the Byzantine Empire. The Emperor continued to reserve the use of purple for himself, but styles had advanced and the imperial robes were likely to be an all-purple cloth embroidered with intricate gold patterns.

The capital of the Byzantine Emperor was Constantinople. In the Emperor's palace there was a special room called the Purple Room where the Emperor's wife gave birth to the heir to the throne. The term Porphyrogenitus, literally 'purple-born', meant both that the child was born in the Purple Room and that he was to inherit the position of the purple-wearing Emperor (as opposed to the military emperors who took the throne by force).

With the destruction of the Byzantine Empire on 29 May, 1453, the bottom fell out of the purple dye industry in the Eastern Mediterranean and the methods and processes were forgotten.

Medieval Splendour

Meanwhile in the West, civilisation had re-established itself and Medieval kings and queens liked to wear purple, as it was still considered a royal colour. In fact even today there is still a lot of purple used by royalty in their official regalia, such as coronation cloaks, crowns and so on.

The Church also got in on the act; Jesus Christ was considered to be the ultimate royalty, so he was depicted wearing purple. Important people within the church, such as bishops, wore purple robes. They also wore amethysts. By now, the amethyst was considered not only a symbol of sobriety but also of chastity, so the bishop's ring often bore a purple amethyst.

Purpure

Purple, known as 'purpure', became one of the five standard colours of heraldry, the conventional design of coats of arms. The other four colours were black, red, green and blue. (White and yellow are not used in heraldry, being replaced with the metals silver and gold.) Of the five colours, purpure was the least often used, but a purple lion did feature on the coat of arms of the district of Leon in Spain. This made its way onto the coat of arms of Spain and from there onto the Spanish flag.

The Shift Towards Blue

Colours are not as fixed to names as most people think, and the name purple started to wander to a different shade. Some time after the fall of the Western Roman Empire and before the 19th Century, the word 'purple' came to mean a bluer colour than the one recognised by the Romans. Tyrian Purple was about two parts of red to one part of blue. Modern purple, on the other hand, is more like the other way around, with one part of red to two parts of blue. It looks something like this:

The Purple Madness

The 18th Century was known as the 'Age of Reason'. It is ironic that one of the most famous people from that era is King George III (1738 – 1820) of the United Kingdom, who was mad. During his periods of insanity, the ruling was done by his son George, Prince Regent, giving us the term 'Regency' for this particular period.

There have been various attempted diagnoses of the madness. One of the most popular theories, although by no means proved, is that the king suffered from 'porphyria', a disease named after the colour purple, as it causes the urine and faeces to have that hue.

Research done in 2003 shows that the king had a very high level of arsenic in his body. This ties in with the porphyria theory – arsenic is a known trigger of porphyria. The arsenic would have been absorbed over the years from various medicaments, and ironically from the very medicine used to treat his madness.

The Mauve Decade

In the mid 19th Century, a variety of purple became all the rage in the fashion shops of Paris. Known as 'mauve' after the French name for the mallow flower which it resembled, it was produced from an expensive dye made from lichens. This was available in Paris but very hard to source in London.

At that time, before the discovery of electricity, cities were lit by gaslight produced from coal. One of the waste products of the gas production was a black tarry substance called coal tar. Chemists were just beginning to realise that coal tar, although it consisted mainly of carbon, hydrogen and oxygen, had the ability to produce all sorts of different chemicals with different properties. This was the beginning of the science of organic chemistry.

William Henry Perkin became a student chemist at the age of 15. In 1856, he was 18 and was experienced enough that his tutors gave him assignments to do on his own – he did them in his garden shed. One such assignment was to find a way of synthesising quinine, the only known treatment for malaria at the time, from coal tar. Perkin experimented with various processes and various by-products of coal tar. In one experiment, he treated aniline (C₆H₅NH₂) and produced a disappointing black gunk. But when he tried to dissolve this in alcohol, he produced a beautiful mauve dye, which he named mauveine.

He was not the first person to make colours from coal tar, but he was the only one who persevered. He found that the dye would fix to silk and a piece of dyed cloth held its colour and did not fade when exposed to the sun. He worked hard to develop ways of making the dye fix to cotton cloth, since most of the textile industry involves cotton. He spent his family's money on setting up a dye-making factory and developed cheap ways of making aniline in bulk. His work paid off; he became the first person to become rich from making synthetic dyes and was the wealthiest chemist in England before he was 20. His Perkin Purple was the same shade as the French mauve, and is shown here:

The artificial dye was so successful that mauve became the colour of the decade (1855 – 1865 approx). Queen Victoria wore mauve to her daughter's wedding in 1858, and a mauve silk gown to the Royal Exhibition in 1862. Charles Dickens wrote:

As I look out of my window, the apotheosis of Perkins's purple seems at hand – purple hands wave from open carriages – purple hands shake each other at street doors – purple hands threaten each other from opposite sides of the street; purple-striped gowns cram barouches, jam up cabs, throng steamers, fill railway stations: all flying countryward, like so many migrating birds of purple Paradise.

Inspired by Perkin's success, others produced lots of different dyes from coal tar, but purple gets the credit for being the first.

Purple Primordial Soup

One of the enigmas of science is why plants are green. Contrary to popular belief, the sun isn't yellow, but green: the sun gives out light at lots of different wavelengths, but it peaks in the green part of the spectrum. But plants reflect green light and don't use it – that's why they look green. So why should plants not use the most important component of sunshine?

According to Shil DasSarma, a microbial geneticist at the University of Maryland, early life on Earth used not chlorophyll, but another chemical called retinal³. It absorbs green light but reflects blue and red, giving it a purple colour. Life at that time would have been confined to the shallows of the world's oceans, the so-called 'primordial soup'.

Chlorophyll, the essential chemical of modern photosynthesis, evolved later and was forced to absorb the blue and red light, since there wasn't much green light available, it having been all absorbed by the retinal. (This is possibly the weak point in the argument.) Because chlorophyll is more efficient than retinal, it took over and plants have been green ever since. But the Early Earth, according to this theory, was purple.

DasSarma's theory is controversial and not generally accepted among microbial geneticists.

Purple In Modern Society

Purple has a strange position in modern society. Due to its royal pretensions, it still can indicate opulence. It is simultaneously too dark and too gaudy for most interior decorating, and as a colour for clothing is considered distinctive enough to be making a statement. In the case of men wearing purple, the statement is usually interpreted as either 'I'm gay!' or 'I'm so individualistic, I don't care if people think I'm gay'. Purple's place in the modern psyche can best be seen by looking at the following examples of its use. We're not going to list things in nature which just happen to be purple. These are places where the colour purple has been chosen to make a point.

• One of the most successful British rock bands of the 1970s was Deep Purple. Their classic numbers include 'Highway Star', 'Space Truckin’' and 'Smoke on the Water'. When the band was formed, the granny of band member Ritchie Blackmore kept on asking them would they play her favourite song, a smooth romantic number called 'Deep Purple', by Peter deRose and Mitchell Parish. This song was totally out of keeping with the style of music the band were aiming for, so they never did play it, but they named the band after it.

• In the book 'The Color Purple' by American author Alice Walker (1982), a field of purple flowers is used to awaken the main character, who has had a miserable life, to the beauty of the natural world around her. Walker received the 1983 Pulitzer Prize for Fiction and the National Book Award. In 1985, the book was made into a film starring Whoopi Goldberg and directed by Steven Spielberg.

• The Purple Heart is a medal awarded to American soldiers who are wounded or killed during combat. The medal is heart-shaped and features a gold head of George Washington on a purple background with a gold border. It hangs from a purple ribbon. On the back are engraved the words 'For Military Merit'.

• The poem 'Warning' by Jenny Joseph (1961), begins:

  When I am an old woman, I shall wear purple
  With a red hat that doesn't go, and doesn't suit me

  It exhorts older women to act eccentrically and not to force themselves to adopt the conventions set by others. It was voted Britain's favourite poem in 1996.

• The poet Gelett Burgess (1866 – 1951) wrote the little ditty 'The Purple Cow' when he was only 29 and regretted it for the rest of his life, as it is the only one of his works that is remembered.

• 'Purple Prose' is English which has been needlessly padded by the addition of lots of unnecessary adjectives and glowing phrases. It is generally disapproved of in most writing circles, but seems to survive in travel brochures and cheap fantasy novels.

• As an example of the effectiveness of a simple website, look at www.purple.com. On the web since 1994, it has just one message and the message is purple.

• 'Purple Rain' is possibly the best-known song by the artist formerly known as 'The Artist Formerly Known as Prince'⁴. It features the lyrics: 'Purple Rain, Purple Rain, Purple Rain, Purple Rain'. In fact, Prince uses the colour purple in much of his publicity.

• 'Purple haze' is a phrase descriptive of the spaced-out state after taking certain hallucinogenic drugs. It has also been used as a name for a particular type of LSD tablet. Über-guitarist Jimi Hendrix released a single of that name in 1967 describing a dream-like state, but claimed it was nothing to do with drugs.

• Nothing rhymes with purple. Except 'curple' and 'hirple', both obscure Scottish words, but they are in the Oxford English Dictionary. Curple is an archaic word for rump, while to hirple is to walk with a limp.

• In Roman Catholicism, the priest's vestments are purple on certain days, although the colour is officially known as violet. According to the Catholic Encyclopedia, 'violet, the gloomy cast of the mortified, denotes affliction and melancholy'. As a result, it is used in the seasons of Lent and Advent, as well as on fast days and ember days, and in ceremonies such as the blessing of holy water and candles, the first part of the Baptism ceremony and the sacraments of Penance and of the Sick. The colour has a similar significance in the Church of England.