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  • Writer's pictureMichael Skalka

Again and A”Gahn” - A Human Invention Machine

Summary: Johann Gahn, an 18th-century chemist, discovered an amazing variety of materials that are still in use today. Read how this little-known scientist made an impact on the world.

A theme that runs throughout many of these essays is that it is hard to contain the energy of those who invent new materials. Once the creative spirit is set ablaze, that fire continues to burn. Such is the case with Johann G. Gahn a Swedish chemist and metallurgist. He lived from 1745 to 1818. This was a particularly ripe age for scientific discovery. Like a 19th-century United States homesteading land rush, discovering elements and chemicals were awaiting those ready to take on the challenge. The steps to discovery were nearly the same for everyone. Get an education, work in a laboratory, surround yourself with chemicals, and the ingredients for some fundamental discoveries are only stifled by a lack of imagination or talent.

Gahn was not a household name then and certainly not a name known to many now, but Gahn was instrumental in making discoveries that placed him among the ranks of the world’s unsung heroes in chemistry. Nearly every single discovery had some relationship to color.

One discovery was built upon another. The alchemist Hennig Brand from Hamburg evaporated urine and found the useful element phosphorus is contained within the solids. A universe of bizarre and intriguing stories awaits those who travel down the path of exploring the uses involved regarding this “yellow gold” of the waste kingdom. Gahn took the safe route. In 1774, he and his colleague C. W. Scheele (another inventor whose namesake is Scheele’s Green) extracted phosphorus from bone ash. When they added nitric acid, it produced phosphoric acid.

It seems the collaborative relationship of Scheele and Gahn was short-lived. Both worked independently on the same intriguing material, barium. The fifty-sixth element in the Periodic Table, barium, as dense as it is, eluded capture as a pure substance. Scheele and Gahn labored over various forms of barium compounds. One of these was barium sulfate. Its use as a filler in a variety of art materials is common. Artificially produced it was called blanc fixe, an extender for pigments that could also lower the oil absorption characteristics of colors that traditionally required a large amount of drying oil to be made into a usable paint.

When barium sulfate is co-precipitated with zinc sulfide, it becomes a material known as lithopone, a basis for lake colors, and further, it has been used as an inexpensive white extender when combined with lead carbonate (lead white.)

Gahn was not looking at barium sulfate as a pigment but as a gateway to understanding and isolating elemental barium. It took about 40 more years of painstaking work to come up with barium in pure form.

Sir Humphry Davy isolated the element via electrolysis. Unfortunately, Davy is no relation to the inventor of Davy’s Grey. Connecting Davy with Gahn and Scheele would be a “hat trick” of epic proportions.

J. G. Gahn did make some solo discoveries. He isolated the element manganese. It provides the natural color found in the gemstone amethyst. Its importance as a metal would come much later. Manganese can be processed to create a greenish-blue color called manganese blue. Unfortunately, it is no longer produced since the waste products created during processing are environmental hazards that are costly to safely dispose of them. Manganese would also find its way into the oil paint industry as a substance that accelerates drying when mixed with linseed oil.

Gahn put his mark on the gemological world. He discovered the semi-precious stone named after him called Gahnite. This mineral is part of the spinel family. The red variety of spinel found its high point in history when it was fashioned into one of the jewels set within the Imperial State Crown of England.

I presume, as every English schoolchild was taught, this crown was given to Edward the Black Prince by Pedro the Cruel, King of Castile, to celebrate the victory of Najera in 1367. How does this relate to pigments you might ask? A variety of spinel that has some of its iron replaced by magnesium, has been used to make a black oil paint called Black Spinel. The color name is not related to an obscure reference to Edward the Black Prince, at least if Pedro the Cruel had anything to say about it. Edward wore the gem rather than grind it into pigment and paint with it.

At the ripe age of 73, in the year of his death, Johanna Gahn still had one last discovery to bring into the world. Teaming up with chemist and business partner, Jons J. Berzelius, they discovered the element selenium amidst the chemicals used in the production of sulfuric acid. Selenium added to molten glass produces a rich, ruby-red color. Used in moderation, it counteracts the tendency of glass to be naturally green and renders it clear.

Gahn’s color pigment claim to fame is sparsely documented and associated with a hue rather than a chemical composition. The color is called Gahn’s ultramarine. A single reference claims that Gahn was one of several discoverers of cobalt aluminate pigments. He observed in 1777, that aluminum compounds combined with cobalt solutions yielded a blue mixture. Gahn’s blue turns out to be a form of cobalt blue. However, it was Thenard who is credited with the development of cobalt blue, derived from oxides of cobalt and aluminum, into a popular colorant twenty-seven years after Gahn’s experiments.

Forty-nine years after Gahn’s work with cobalt and aluminum, artificial ultramarine blue was introduced, thus solidifying the blue market with two outstanding performers, French Ultramarine and Cobalt Blue. Gahn’s blue was relegated to a historical footnote. With a bit more work he might have been able to claim Cobalt Blue as his own discovery exclusively.

Colors named after the inventor of the pigment have not had a great deal of marketing success. Two modern winners are Hooker’s Green and Davey’s Gray. Perhaps it is time to get a bit more creative with color names and tube designs. How about a famous Royalty Color series? Sure, we have the choice of Kings Yellow but what about expanding the royal name association with the following:

(Edward the) Black Prince Black,

Kublai Khan Cobalt,

Attila the Hun Hansa,

and my personal favorite, Pedro the Cruel Cadmium.

Syntax of Color

(Originally published – 2006, re-edited 2023)

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