Legendary Prussian blue, the color that can save or kill lives

One day in the early 18th century, Johann Conrad Dippel, the most notorious resident of Frankenstein Castle who possibly inspired the writer Mary Shelley, was in his laboratory in Berlin preparing his “elixir of life.”

The controversial theologian, who was even imprisoned for his beliefs, opted for alchemy and, after failing in his attempts to convert common metals into precious metals, he dedicated himself to creating that “universal medicine” that, he claimed, cured all ills.

His “Dippel oil”, a concoction whose appearance was similar to liquid tar with such an unpleasant taste and smell that during World War II it was used to make water undrinkable and dehydrate the enemy, it was a distillation of horns, leather, ivory. and decomposed blood to which he added potash (potassium carbonate).

At the same time, in the same place, a Swiss color creator named Johann Jacob Diesbach was preparing a batch of crimson lacquer, a red pigment made from cochineal, an insect brought from Latin America, for which he also needed potash. But he didn’t have enough, so he borrowed part of Dippel’s.

The next day, what they found in the laboratory, surprisingly, was blue, instead of the expected red.

It turns out that the Dippel potash that Diesbach used was contaminated with blood, which contained iron, and that triggered a chemical reaction so complicated that, if not for that accident, it might not have been discovered for years.

As the French chemist Jean Hellot would say in 1762, “perhaps nothing is more peculiar than the process by which Prussian blue is obtained … And if chance had not intervened, a profound theory would be necessary to invent it”.

Precious

The haphazardly created color was gorgeous, in every sense of the word.

It was not only beautiful but valuable.

Blue has always been an elusive color that, despite being all around us, often feels out of reach: We cannot touch the blue of the sea or feel the blue of the sky.

And having it in your hands to color the world with it, until that moment, had not been easy either.

In Ancient Egypt they developed a pigment known as “Egyptian blue”, whose main ingredient was a rare gem called azurite. Although it was used for thousands of years, the method and science behind its creation fell into oblivion.

Other early blue pigments were made by grinding turquoise and lapis lazuli, and this last semi-precious stone was still the basis at the beginning of the 18th century. the most stable, brilliant, purest and strongest of the few blues available in Europe.

It had arrived in the Middle Ages and dramatically changed art, opening the gates of heaven to artists like Giotto, the father of the Italian Renaissance, who in the Scrovegni chapel in Padua raised that blue to divine status.

They called it ultramarine, because lapis lazuli came from there, that almost mythical stone that, back then, could only be found in a small mine at the far end of what is now Afghanistan.

To reach Venice, at that time the world leader in color, he traveled some 5,600 kilometers, crossing mountain ranges, deserts and, finally, the Mediterranean Sea.

Not for nothing was ultramarine blue worth its weight in gold, literally: for centuries an ounce of that color cost an ounce of gold.

It was a luxury.

Because, the possibility of creating a real, wonderful, deep, profitable and viable blue was immensely attractive.

Serendipity and science

While serendipity was the starting point, its creators immediately recognized the value of their “mistake.”

Later experiments led them to produce a pigment that was considerably less expensive than ultramarine, more stable than copper-based blue, and more versatile than indigo.

It was an immediate success.

Diesbach and his partner Johann Leonhard Frisch sent the new invention to the four corners of the world and soon became rich.

Wallpaper, porcelains, stamps and flags were dyed blue, and in 1709 the pigment became the official color of the Prussian army uniform, earning it the name “Prussian blue”, although in Germany it is known as Berlin blue or Berlin blue.

Its composition was the subject of speculation as the manufacturing method remained secret until 1724, when it was revealed.

The recipe?

Take a mixed solution of alum and green vitriol and add to it a solution of alkali previously calcined with ox blood. That gives a greenish precipitate that turns blue when boiled with salt alcohol. (Meat or other animal matter was soon shown to be as effective as the blood of an ox.)

Art and much more

Unsurprisingly, Prussian blue broke into the art world, with a huge demand for both oil paintings and watercolors.

From “Entombment of Christ” (1709) by the Dutch painter Pieter van der Werff, the earliest verified use in a painting …

… to “The Great Wave off Kanagawa”, created by the Japanese artist Katsushika Hokusai on the other side of the planet …

… without forgetting the work of Picasso, who with Prussian blue expressed his sadness over the tragic death of a close friend in his Blue Period (1901-1904)…

… and so many others.

But the pigment also began to be used – and continues to be used – in areas far from art, although sometimes they seem close, as in the case of the work of the English botanist Anna Atkins, who published the first exclusively illustrated book in history with photographs.

He took them using a photographic procedure called cyanotype, which produces a negative copy of the original in a Prussian blue color, called a cyanotype.

The process had been learned from its inventor, renowned astronomer and family friend John Herschel.

The latter, appreciating the light-sensitive properties of Prussian blue, used it to produce the first blueprints or blueprints, allowing simple and efficient reproduction of diagrams, technical drawings, engineering designs, and blueprints.

For a century since its invention in 1842, that photocopying process was the only cheap way to copy drawings.

Since then, the uses of pigment in various technologies have continued to multiply.

In this century, for example, its ability to transfer electrons efficiently made it an ideal substance for use in sodium ion battery electrodes, used in telecommunications and data center applications.

But perhaps the most curious thing is that Prussian blue is a color that heals.

Essential medicine

Indeed: Prussian blue is on the World Health Organization Model List of Essential Medicines as a specific antidote for heavy metal poisoning.

It is used to treat people who have been internally contaminated with radioactive cesium or highly poisonous thallium, as happened in the radiological accident in Goiânia, Brazil, in 1987, when a disused medical radioactive source was stolen from an abandoned hospital.

In such cases, patients ingest pigment capsules, and the pigment traps dangerous metals in its structure, prevents the body from absorbing them, and reduces the time it takes for radioactive material to leave the body, mitigating damage.

In the case of cesium, it reduces it from about 110 days to 30 and for thallium, from about eight days to three.

On the other hand, in addition to several applications in cutting-edge medical technology, remains the pathologist’s primary tool for detecting lead poisoning.

And as a stain it is widely used for both diagnostic and research purposes to detect the presence of iron in biopsy samples, especially in tissues such as bone marrow and spleen.

Although iron is essential for life, it is also toxic due to its ability to form free radicals that can damage cells.

The dark side

For thousands of years it was known that many plant parts, such as cherry bay leaves, peach seeds, cassava, and even apple kernels were lethal if administered in concentrated form, and that their poison was often detected by their distinctive smell of bitter almonds.

But even though they were used even in court executions – ancient Egyptians had the “peach penalty” and Romans “the death of the cherry tree” – it wasn’t until 1782 that a Swedish pharmaceutical chemist, Carl Wilhelm Scheele, identified the ingredient. active toxic.

He discovered that if he mixed Prussian blue with dilute sulfuric acid, he could produce a gas that was colorless, soluble in water and acid.

In German they called it Hydrocyanic acid (literally “acid blue”) due to its derivation from Prussian blue; in English, prussic acid.

Today we know it as hydrogen cyanide (HCN), but we call it by its more common abbreviated name: cyanide, which comes from the Greek word for dark blue.

It is extremely toxic. If ingested by a human, it is rapidly absorbed, irreversibly binds to the iron atom in hemoglobin, and prevents the blood from transporting oxygen to the cells and tissues of the body.

Palpitations, headache, and drowsiness are followed by coma, seizures, and death from suffocation.

And sometimes a slight almond smell remains.

Such an effective poison soon became a weapon, one that not only served in its liquid form to kill individuals, but, as a gas, was ideal for mass murder, such as those perpetrated by the Nazis.

“Visited Treblinka [el campo de exterminio] to find out how they carried out their extermination ”, the commander of the Auschwitz concentration and extermination camp, Rudolf Hoss, related in his sworn statement.

“The group commander told me that he had liquidated 80,000 in the course of half a year. He was primarily interested in liquidating all the Jews in the Warsaw ghetto. He used monoxide gas and I didn’t think his methods were very efficient.

“So in Auschwitz I used Cyclon [Zyklon] B, which was a crystallized prussic acid that was dropped into the death chamber. It took three to 15 minutes to kill the people in the chamber, depending on the atmospheric conditions. We knew people were dead when the screaming stopped. “