• Michael Skalka

The Discovery of Thenard Blue (Cobalt Blue)

A new series of essays on the science behind the origins of pigments.

An hour and 40-minute drive from Paris will take you to the town of La Louptière-Thénard. The town appears to have no museum to honor the birthplace of the chemist, Jacques Louis Thenard. (May 4, 1777 – June 21, 1857) However, in 1865 his accomplishments were so impressive it motivated the native village authorities to add his last name to the little town of La Louptière. Today, La Louptière-Thénard is a community devoid of tourist attractions with the exception that, through no fault of its own, it is in the Champagne region of France. I speculate that some of the terroir of this sparkling wine making region infiltrated young Jacque and that will become clear later in this essay.

It is clear when researching any of the chemists that discovered elements or compounds, they possessed special talents and insights far beyond the capabilities of average people. They struggled to understand and fill in the voids in scientific discovery that, had they been already know, would make putting the pieces together of how materials behaved and the mechanism needed to isolate, refine and prove they were new elements or compounds much easier.

Thenard benefited by mentoring and his desire for discovery. The breath of his discoveries was broad and many of the materials he studied are still in use today. I believe it was his genius along with his association with some of the best scientists of his period that launched Thenard on the path to greatness. Some of his mentors have and will be discussed in future Syntax of Color essays.

Jacques Thenard went to Paris to receive his education and soon his work caught the attention of the pharmacist and chemist Louis Nicolas Vauquelin along with Antoine Francois, comte de Fourcroy. Vauquelin made a number of ground breaking discoveries in chemistry. Fourcroy standardized the nomenclature of chemistry that is still in use today. In 1798, at the age of 21 Thenard had impressed Vauquelin enough to gain an appointment to the Ecole Polytechnique. Six years later, Thenard replaced Vauquelin who retired from his position at the College de France. A few years later Thenard replaced Fourcroy in his teaching position. By 1830 Thenard was a prominent member of a number of chemistry societies and was showered with numerous awards and accolades, including knighthood in the Legion of Honor.

So now you know some of the highlights. Let’s explore how discovery, chemistry and color work together. Thenard was interested in acids. No, not the mind-altering kind, but more like acetic, hydrochloric, and oxalic acid in relation to the chemistry of esters. These acid alkyl reactions form the basis for the foundation of many plastics, resins and fabrics, like polyester, we use today. Thenard also studied metals and the means to purify them. His quest to attain highly refine nickel led him to focus on cobalt. By understanding the properties of cobalt, Thenard heated alumina with cobalt arsenate or cobalt phosphate and created a blue pigment. This work to produce a blue pigment was motivated by the French government’s call to develop a substitute for lapis lazuli, the natural compound that is the basis of ultramarine blue. Thenard even did light fastness testing of his blue pigment to assure himself and others that it had the same permanence as natural ultramarine. In other experiments related to finding oxides of metals he tested both realgar and orpiment, two ancient pigment to prove they lacked the ability to form oxides. In 1812 Thenard studied oxygen and sulfur to create one of his best-known discoveries, hydrogen peroxide. Interestingly, the modern method for making hydrogen peroxide involves the use of anthraquinone. Anthraquinone come in a variety of molecular formations. One of them is used in the paper making process and another is the pigment Anthraquinone Blue, also known as Indanthrone Blue. These are wonderful examples of how materials form a complex web of relationships with each other. Further, Thenard would likely never imagine that his discovery of hydrogen peroxide would one day be refined to be the oxidation component in a formulation of rocket fuel. Discoveries built one upon one another can literally propel us to the stars.

Lastly, Thenard’s work on acids has an interesting link to wine. I never thought that I could incorporate my interest in wine making with the history of pigments. It quickly becomes clear when studying the complexities of the wine making process that a combination of biological and chemical functions woven together, make wine possible. Yeast and the chemical components in grapes and other fruits are filled with chemical interactions. Thenard’s study of acids indicates an interesting coincidence. He devoted time to studying the reaction of acids to alcohol and three of those acids stood out. Citric, malic and tartaric acids. These acids are major components in wine that shape its fundamental character. So, the acids found in wine, the study of esters and Thenard’s roots in the Champaign region of France create an interesting intersection of related things. To top it off, Thenard’s methodology and process of analyzing how materials react, served as the basis for Justus von Liebig (a major figure in biological and agricultural chemistry) while studying in Paris. Liebig studied how yeast can transform sugar into alcohol, a key process in the production of wine.

Despite working with many dangerous chemicals over his life, Thenard lived until 80 years of age. While early on, the pigment Thenard’s Blue was associated with the inventor by name, the more popular name, Cobalt Blue, PB 28, a Cobalt Aluminate Blue Spinel (CoAl2O4) produced by combining, a mixture of Cobalt (II) Oxide, and Aluminum (III) Oxide in a furnace devoid of oxygen. It is a staple in nearly every color manufacturers line of art materials. It shares many of the same spectral color curve characteristics with artificial ultramarine, but lacks much of the violet undertone of ultramarine. I will come back periodically to Jacques Thenard in future essays as other giants in the world of chemistry serve as subjects for exploring other amazing scientific and color pigment discoveries.

The Syntax of Color

The Syntax of Color

Volume 8, No. 1

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© The Syntax of Color  SyntaxofColor  - Michael Skalka

United States