Cobalt
On May 29, 1945, shortly after the liberation of Holland, Han van Meegeren, an artist and art dealer, was arrested for collaborating. Not only had he amassed a suspicious fortune during the Nazi occupation, he had sold Christ and the Adulteress, an early work by Vermeer, to Hermann Göring. If found guilty, he could be hanged.1
Van Meegeren not only vigorously denied the accusation, but countered with a claim of his own. The “Vermeer,” he said, wasn’t really a Vermeer at all: he had painted it himself. At worst, he said, he was guilty only of forgery, and, since he had completely fooled the Reichsmarschall, should he not in fact be celebrated as a Dutch hero? Some of the paintings that he alleged to have passed off during his career as a forger—several more Vermeers and a couple of Pieter de Hoochs, among others—were on display in museums and had been hailed by critics as long-lost masterpieces. Van Meegeren claimed to have made 8 million guilders (around $33 million today). When prominent museum directors and critics refused to believe him, Van Meegeren found himself in the unusual position of having to persuade people of his guilt.
He had, he told the court, specialized in Vermeers because of the huge gap in that artist’s oeuvre—most of his known paintings are from when he was an older man—and the dissonance between his style as a young man and that of his later years. Van Meegeren had used a composition from a Caravaggio for one forgery—Christ and the Pilgrims at Emmaus—knowing that art historians were desperately looking for proof of the theory that Vermeer’s style had an Italian origin. He had also paid attention to the technical details. Rather than using the traditional linseed oil as his paint medium he had used Bakelite, a plastic that sets solid when heated. This let him fool the standard X-ray and solvent tests used to determine the age of oil paintings, which take much longer to harden. He had painted on old canvases that had authentic craquelure (the network of tiny fissures that develop in old paintings) and had only used pigments that would have been available in the seventeenth century2—in every case, that is, except one. The giveaway was a particular shade that was found, upon closer examination, to contain a pigment that wasn’t created until 130 years after Vermeer’s death: cobalt blue.3
It is not surprising that Van Meegeren had missed the switch. Cobalt blue was, after all, one of the blues created specifically as a synthetic substitute for ultramarine.4 A French chemist, Louis-Jacques Thénard, decided the key would lie in cobalt, the element Sèvres potters used in their blue glazes, just as it had been used to make the sky-colored tiles on the roofs of Persian mosques. It was also present in the famous medieval iris-blue glass at Chartres and Saint Denis in Paris, and in the cheap artists’ pigment smalt. In 1802 Thénard made his breakthrough: a mixture of cobalt arsenate or cobalt phosphate and alumina, roasted at high temperatures, produced a fine, deep blue.5 The chemist and author George Field, writing in 1835, described it as “the modern improved blue . . . neither tending to green nor purple, and approaching in brilliancy the finest ultramarine.”6
The presence of cobalt blue in Van Meegeren’s work, though, had unmasked him, and his works were quietly taken down from museum walls and discreetly stashed away. In November 1947, two years after his arrest, he was finally found guilty. Not of collaboration with the Nazi regime—although a book of his drawings had been found in Hitler’s personal library, bearing the inscription “To my beloved Führer in grateful tribute”—but of forgery.7 He was sentenced to a year in prison, but he died—some said of a broken heart—the following month.
Indigo
In 1882 the British Museum acquired an object it would take 11 decades to understand. The artifact is a tiny clay tablet, around 2.75 in. square and 0.8 in. thick, covered in minute text written in Babylon sometime between 600 and 500 B.C. In the early 1990s, when academics finally cracked the translation, they discovered that what had been inscribed in the still-damp clay thousands of years before was a set of instructions for dyeing wool dark blue. Although it isn’t mentioned, the description of the process—with all its repeated dipping—indicates that the dye was indigo.
For a long time it was presumed that both the seeds for the indigo-bearing plants and the knowledge of how to turn them into a dye the color of the night sky had blown west with the winds of trade: from India to the Middle East and Africa. (An imprint of this assumption survives in the word itself. Its etymological root is the Greek indikon, which means “a substance from India.”) Now, though, this seems unlikely. Instead, people seem to have discovered the process independently, and at different times, across the world. There are many different species of plant that produce indigo—woad [here] is one—but the one most coveted for its colorant is Indigofera tinctoria.1 For a dye-producing workhorse it is a pretty shrub, with small, slightly dusty green leaves, pink blooms that look like miniature sweetpeas, and dangling seedpods.2
Although, unlike woad, I. tinctoria is a “nitrogen fixer” and therefore good for the soil, it is still temperamental and prone to mishap.3 Farmers in Central and South America, for example, not only had to deal with the usual risks—fluctuating prices and rainfall, sinking trade ships—but also with a host of others of biblical proportions, including earthquakes, and plagues of caterpillars and locusts.4 Even once the crop was harvested the poor, nerve-shredded farmers couldn’t sleep easy.
Even today, with more chemicals and equipment at our disposal, the process for extracting the dye from the leaves is cumbersome; the traditional process, done entirely by hand, was far worse. First, the greenery was fermented in an alkaline solution. The liquid was then drawn off and vigorously beaten to aerate it. This caused a blue sediment to form, which was then dried into cakes or blocks to be sent off to market.5
The result is worth the effort. In addition to the vivid color, indigo ages beautifully, as any denim aficionado worth her Japanese selvage will confirm. It is also the most colorfast of the natural dyes. Where it has been used in combination with others to create colors like green or black, it is often only the indigo that remains. The phenomenon is so common that the now sky-colored foliage in Renaissance tapestries is said to suffer from “blue disease.”6 Unlike most dyes, indigo doesn’t need a mordant to fix it to fabric. While the relatively weak indigo content in woad could color absorbent fibers like wool, the dye from other indigo-bearing plants could be up to 10 times stronger, more than powerful enough to saturate less accommodating vegetable fibers like silk, cotton, flax, and linen.7 Fabric dipped into the chartreuse-hued dye vat changes color upon coming into contact with the air, turning from yellowish green to sea green before settling on a deep, stolid blue.
Indigo is woven into the burial customs of many different cultures globally, from Peru to Indonesia, Mali to Palestine. Ancient Egyptian dyers began threading thin lines of blue fabric into the edges of their linen mummy cloths from around 2400 B.C.; a state robe found in the extensive funerary wardrobe of Tutankhamen, who reigned around 1333–1323 B.C., was almost entirely indigo.8 The dye has made inroads into other cultural spheres too. Males of the Tuareg tribe in northern Africa are given tagelmusts, or headscarves, at a special ceremony that marks their transition from boy to man. The most prestigious in a community wear the glossiest indigo tagelmusts, whose gloriously resonant hue is developed through multiple rounds of dyeing and beating.9
Because it has always been so highly prized, indigo has, from as far back as records and educated guesswork allow, been a bedrock of global trade. The wealthiest Romans could import indigo at 20 denarii a pound, around 15 times the average daily wage (prices were so high that some merchants apparently tried their luck selling a counterfeit made from pigeon dung).10 Adding to the expense were the restricted trade routes. Before Vasco da Gama nosed his ship around the Cape of Good Hope and opened up another passage to the East, goods traveling westward had to make their way overland through the Middle East or around the Arabian Peninsula. This route was unpredictable and difficult to navigate, and prone to civil unrest, and heavy duties were
levied by the various rulers along the way, ratcheting up prices for those at the end of the journey. Obstacles were endless. In 1583 there was a dearth of camels following an extreme dry spell and caravans ground to a halt. After nearly causing a diplomatic incident in Bayana, India, by outbidding the emperor’s mother for “twelve carts loaded with nil [indigo],” a British merchant lost both his precious cargo and his life in Baghdad on the journey home.11
Despite Europe’s slow adoption of imported indigo—chiefly due to the resistance from local woad farmers—the rise of colonialism in the sixteenth and seventeenth centuries, and the prospect of the fortunes to be made, overcame lingering resistance; trade became almost frenzied. In just one year, 1631, seven Dutch ships carried a total of 333,545 pounds of indigo back to Europe, a cargo worth five tons of gold [here]. Over in the New World, the Spanish began producing indigo on a commercial scale almost immediately after conquering Guatemala in 1524; it soon became the region’s principal export.12
New trade routes, combined with ample use of slave and forced labor in the New World and India, drove prices downward. Armies began using indigo for their uniforms. Napoleon’s Grande Armée, for example, consumed around 150 tons per year.13 (French infantrymen still wore madder or alizarin red [here] trousers until the First World War; this was replaced with indigo when they realized that it was making them too easy a target.) Naturally, after William Perkin unlocked the secret to aniline dyes in 1856, a man-made version of indigo was only a matter of time. After an initial breakthrough in 1865, it would be another 30 years before the German chemist Adolf von Baeyer, with financial backing from the German pharmaceutical giant BASF to the tune of 20 million gold marks, finally got “Pure Indigo” to market.
From being a luxury on a par with Tyrian purple [here], indigo has become the color of the “blue-collar” workforces, not only in Europe but also in Japan and China, where the dusty blue Mao suit became ubiquitous in the twentieth century.14 It is, strangely enough, this workwear association that has proved this pigment’s most enduring legacy, in the form of blue jeans.15 Although it peaked around 2006, the global denim industry, which is dominated by the classic indigo blue, was worth $54 billion in 2011.16 Jeans have been a wardrobe staple since the 1960s, and, as Giorgio Armani is often quoted as saying, they “represent democracy in fashion.” In them one can be at home, and understood, everywhere.
Prussian blue
Sometime between 1704 and 1706, in a dingy room in Berlin, a paint manufacturer and alchemist called Johann Jacob Diesbach was making up a batch of his signature cochineal red lake (a kind of paint made using an organic colorant and an inert binder or mordant) [here]. The chemical process was a relatively simple one using iron sulfate and potash. On this day, though, when it came to the crucial stage, Diesbach realized he had run out of potash. He bought some more from the nearest supplier and carried on, but something wasn’t right. When he added the potash, the mixture did not turn a strong red, as it ought to; instead it was pale and pinkish. Perplexed, he began trying to concentrate it. His “red lake” solution turned first purple, then a deep blue.
Diesbach found the man who had sold him the potash, a disreputable fellow alchemist and pharmacist called Johann Konrad Dippel, and demanded an explanation. Dippel deduced that the iron sulfate had reacted strangely with potash because the latter was adulterated with animal oil. The reaction had created potassium ferrocyanide (a compound still known in German as Blutlaugensalz, literally “blood alkali salts”), which had combined with the iron sulfate to produce iron ferrocyanide, a compound we now know as Prussian blue.1
This was a very auspicious time for a new blue. Ultramarine [here] remained the ideal, but it was still fiendishly expensive and supply was inconstant. There was also smalt, blue verditer, azurite, and even indigo [here], but these were all slightly greenish, with poor coverage and not particularly reliable once on the canvas.2 Prussian blue was a revelation. A deep, rather cool color with tremendous tinting strength and the ability to create subtle tones, it also behaved well with lead white [here] and combined with yellow pigments like orpiment [here] and gamboge [here] to make stable greens. In his pigment compendium of 1835, George Field called this “rather modern pigment,” “deep and powerful . . . of vast body and considerable transparency.”3
Dippel, who may have been dishonest but clearly did not lack business acumen, began selling it around 1710. The formula remained a secret until 1724, when an English chemist called John Woodwood published the method for making Prussian blue in the Philosophical Transactions of the Royal Society.4 By 1750 it was being manufactured across Europe. Unlike many other pigments of the time (and despite the “cyanide” in its chemical name), it isn’t toxic; it was also a tenth of the price of ultramarine. It did have drawbacks, though, becoming discolored by strong light and alkalis. W. Linton, author of Ancient and Modern Colors (1852), while conceding that it was “a rich and fascinating pigment to the colorist,” said it was “not to be depended upon,” and yet fretted it was difficult to avoid.5
The color is seen in the works of artists as diverse as William Hogarth, John Constable, Van Gogh and Monet. Japanese painters and woodblock craftsmen were delighted with it. It was also the blue Picasso favored during his blue period in the first years of the twentieth century after the death of a friend, its transparency giving cool depths to his melancholic settings. It is still very much in use: Anish Kapoor’s flattened topographical sculpture A Wing at the Heart of Things, created in 1990, is made from slate coated in Prussian blue.
The pigment has been busy colonizing other industries too: it has long been used in wallpapers, house paints, and textile dyes. John Herschel, a nineteenth-century British chemist, astrologer, and photographer, worked out how to use it in combination with photosensitive paper to make a kind of proto-photocopy. The results, which showed up as white marks on a blue ground, became known as “blueprints,” a word that has come to denote any technical drawing.6 It is also used to treat people with thallium and radioactive cesium poisoning, as it prevents the body from absorbing them. The only side effect is alarmingly blue feces.7
Remarkably, for most of its history no one was quite sure exactly what Prussian blue was; they knew the steps to take to make it, but were unclear on exactly what was reacting with what. Perhaps, though, that isn’t so remarkable: iron ferrocyanide, a crystalline blue solid, is a complicated compound with a dizzying lattice structure at a molecular level. That such a thing was created by happy accident seems almost miraculous. As the French chemist Jean Hellot remarked in 1762:
Nothing is perhaps more peculiar than the process by which one obtains Prussian blue, and it must be owned that, if chance had not taken a hand, a profound theory would be necessary to invent it.8
Egyptian blue
William, a small ceramic statuette of a hippopotamus, can now be found in the Metropolitan Museum of Art, around 6,000 miles and some 3,500 years away from his point of origin: the banks of the Nile in Egypt. Although to our eyes he cuts rather a beautiful figure, with his blue-green glazed skin decorated with flowers, to his creators he would have seemed far less benevolent. Hippos were dangerous creatures, both in real life and in mythology, where they might upset your journey to the underworld. Figurines like this had their legs broken (William’s have subsequently been repaired) and were placed in tombs as talismans to protect their occupants on their onward journeys.
The Egyptians were uncommon in valuing blue: most Western cultures didn’t even possess a separate word for the slice of spectrum between green and violet. For the ancient Egyptians, though, the color represented the sky, the Nile River, creation, and divinity. Amun-Ra, the empire’s principal deity, was often depicted with blue skin or hair, a trait that other gods borrowed from time to time too. The color was thought to dispel evil and bring prosperity, and was much sought after in the form of beads, which in themselves were believed to possess magical protective qualities.1 Although the Egyptians also
used and valued other blues, including turquoise and azurite, both had their disadvantages: the former because it was rare and expensive, the latter because it was hard to carve. So from the time Egyptian blue was first manufactured, sometime around 2500 B.C., it was put to frequent use. Scribes wrote with it on papyri and it has also been found making up hieroglyphics on walls, used as a glaze on funerary objects, and decorating coffins.2
It was the Romans who first referred to the pigment as “Egyptian blue”; the originators themselves called it, simply, iryt (artificial) hsbd (lapis lazuli).3 Its chemical name is calcium copper silicate, and the raw ingredients used in its manufacture were chalk or limestone; a copper-containing mineral, such as malachite, which gave it the blue color; and sand. These were likely fired together between 1,742 and 1,832°F, to create a brittle, glassy solid that was ground down and then refired at between 1,562 and 1,742°F to produce an intense blue that was long-lasting and versatile.4 Not only was it resistant to alkalis and acids but it also lasted well in strong light. Depending on how finely it was ground, it could be as dark as lapis lazuli or as pale as turquoise; if it was applied over a dark base layer it could be almost electric. Producing it was an extraordinary technical challenge. Not only did the ingredients need to be fired together at precise temperatures; the oxygen levels needed to be regulated too.
Mysteriously, given the existence of texts describing it, the manufacture of Egyptian blue petered out.5 Examples from the thirteenth century have been found in Italy, but it is believed this was due to reuse of old pigment stock—small balls of Egyptian blue are often found in Roman excavations.6 Elsewhere, artists began to favor ultramarine [here] from around the ninth century.7 One explanation is that a decreasing demand for blue (before the twelfth-century revival) meant that people stopped bothering to pass the secret down and the technical skills were lost. Alternatively, perhaps a shift in the idea of preciousness is to blame. While modern chemists marvel at the skill needed to make Egyptian blue, Western artists and patrons seem to have preferred raw materials with intrinsic value, like ultramarine.
The Secret Lives of Color Page 14