If we look at the Earth from the stratosphere, it is clear that we live on the Blue Planet. However, the colour that characterizes our planet is very difficult to find in nature and the scarcity of the sources of the materials used to obtain natural dyes and pigments—be they animal, vegetable or mineral—has meant that for the longest time blue pigments were yearned-for as much as they were highly valued.
This motivated a constant search for alternatives, mainly through research and chemical synthesis, from which emerged these five pigments that have made history.
>> Behind each picture you will see an artwork produced with that pigment.
This is possibly the first synthetic pigment in history, since it was already being used in Ancient Egypt in the second millennium BC to paint their elaborate murals. But after the fall of the Roman Empire, its complex process of preparation fell into oblivion. It involved mixing in appropriate proportions limestone and Nile sand with copper-rich minerals such as malachite or azurite and heating this mixture to about 800°C. If the process was done correctly, blue crystals (a silicate of calcium and copper) were obtained, which were pulverized and later mixed with some adherent substance, such as egg white or resin, for its application.
The secret of its preparation was recovered in 1815, when the English chemist Sir Humphry Davy investigated it. And Egyptian Blue once again became fashionable in the first decade of the twenty-first century with the discovery that it exhibits an intense infrared luminescence when exposed to ultraviolet light. This has led to the study of its possible application in biomedicine and has also allowed us to see the Egyptian paintings with new eyes, because the enormous stability of the pigment makes it maintain that luminescent capacity even after thousands of years.
Ultramarine landed in Europe through the Italian ports in the fourteenth century and immediately became the most regarded and valued pigment. Due to its scarcity and the difficulty of its preparation, it became more expensive than gold, so the great painters reserved it almost exclusively to paint the garments of Christ and the Virgin. Legend has it that Michelangelo left his painting “The Entombment” unfinished due to a lack of funds to acquire the prized pigment.
In 1824, the French authorities offered a prize of 6,000 francs for anyone who was able to produce a more affordable alternative. Four years later, the prize was given to the French chemist Jean Baptiste Guimet, who had developed a secret method for obtaining a synthetic equivalent called “French ultramarine” and which, after production began in 1830, replaced the natural pigment.
However it happened, the method of obtention involved the oxidation of an iron salt with potassium ferrocyanide to obtain an insoluble white compound called Berlin white, that, when oxidized, became hexacyanoferrate, which is blue in colour.
Diesbach began producing and selling his new blue, which soon gained great popularity among artists. But its importance was to transcend painting starting from 1842, when the English astronomer John Herschel discovered the great sensitivity of the compound to light, which made it the ideal medium or system to make copies of maps, plans and drawings, thereby leading to the appearance of the technology that is behind today’s photocopiers.
Thénard had been commissioned by the French minister Chaptal to obtain a new blue pigment, in view of the scarcity and high cost of lapis lazuli, and also to improve Prussian blue, which tended to fade when mixed with other colours and to become greyish green when combined with white. The chemist focused his research on cobalt compounds—it had been known since 1777 that they were responsible for the blue colour of some minerals—and specifically on cobalt arsenate, used to colour the porcelain from Sèvres.
In this way, he found that if he heated a mixture of alumina (aluminium oxide) and cobalt arsenate, he obtained a pigment of a deep vibrant blue. Furthermore, it was stable against the action of sunlight and the exposure to acids and bases (unlike indigo, another widely-used blue pigment, which oxidizes relatively easily with light and air and requires the application of a protective varnish).
The new colour, named bleu Thénard, began to be produced in France in 1807.
While experimenting with materials that could be applied to electronics, they discovered that upon heating a mixture of yttrium, indium and manganese oxides, the material acquired an intense blue colour. This new compound (YIn1−xMnxO3), whose molecules are organised in a structure that causes it to completely absorb the green and red regions of the spectrum, produces a blue that is particularly clean or pure.
Its unpronounceable name, Blue YInMn, comes from the chemical elements that give it its properties: Yttrium (Y), Indium (In) and Manganese (MN). By varying the ratio of the last two elements, one can adjust the personality of this vibrant blue.
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