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  • Writer's pictureMichael Skalka

The Spoils of Our Labors - Indanthrone Blue

Updated: Jun 18

Summary: The Spoils of Our Labors - Indanthrone Blue explores the discovery of pigment manufacturers have used to add a blue hue to a line of oil paint. This essay examines the work of Rene Bohn and his work of color making.


Anyone who has traveled to a vacation area or passed through numerous airports has seen this shirt. “I Visited (fill in the location name,) and All I Got Was This Lousy T-Shirt.” Ubiquitous and absolutely annoying, it certainly beats the shirt that says, “I’m With Stupid.” That shirt indicates a triple problem. 1. Who with any intelligence would wear such a shirt? 2. Who would want to be seen with a person wearing that shirt? 3. Finally, if the statement on the shirt were true, why would you maintain a relationship with a person of such meager intellect, and further, why would you advertise it?



Aerial view of Ludwigshafen, Germany
Aerial view of Ludwigshafen, Germany

The “Lousy T-Shirt” statement comes to mind when I think of Rene Bohn. He is not quite a household name, but when it comes to pigment fabrication, who but a few, has any name recognition in the field of pigment chemistry? Rene was a dye chemist born in 1862 and died in 1922. In 1901 at the age of 39, Rene had hit his stride. He made two major pigment discoveries. He synthesized both Flavanthrone and Indanthrone.


Flavanthrone is a synthetic yellow dye still in use today. Indanthrone is a blue pigment that several artists’ paint manufacturers maintain in their inventory. It is unfortunate that Bohn could not have created a red pigment, completing a color manufacturer’s version of a “hat trick” thus developing his own primary triumvirate that could have dominated the world until a new group of pigments were discovered.


The creation of Flavanthrone would be cause enough for celebration. This yellow dye is derived from flavonoids, a group of natural pigments that make up most of the yellow, red, and blue colors in both fruits and flowering species. Flavonoid-based colorants are part of the foods we are encouraged to consume. Recent campaigns to get consumers to eat a “colorful” diet became an easy way to remind us to eat fruits and vegetables that are red and yellow and filled with flavonoids. Carrots are the exception. They belong to a different but equally important color group.


Indanthrone blue was touted as a substitute for indigo, a natural dye plant that provided the blue color for denim fabric, of which pants were made that clothed generations. Indigo will be the subject of another Syntax of Color essay. The notion that a synthetic dye could be substituted for a natural one needs to be contemplated a bit. Natural materials are subject to seasonal growth cycles, weather, harvest labor availability, local and national politics, transportation from a remote location, and many other potential impediments to bringing the raw product to a manufacturing plant. Natural materials need refinement once they arrive at the factory. Quality must be checked and availability is subject to the factors previously listed that alone or together can create an interruption in supply. After final processing, the colorant enters the economic market with other product lines and competes on price, performance, and many related factors.


Synthetics may be complex to manufacture, but once a process is mastered, it may have fewer variables that interfere with production. Assuming the raw chemicals are less expensive and plentiful enough to outweigh the cost and processing of natural materials in large-scale manufacturing, synthetic colors provide a steady, abundant, consistent product that natural colorants cannot easily match.


Indanthrone blue is in a family of colorants called “vat dyes.” It is a dye pigment suitable for coloring fabrics but can also be made in a dried powder form to provide color for paints, plastics, and other materials. Indanthrone is a tough, weather, and lightfast pigment that is suitable for a variety of demanding applications. It is prized in the automobile industry, along with a few other organic pigments, for its durability. Car manufacturers love pigments, like Indanthrone blue that have high tinting strength but can be formulated to create translucency in a metallic-based mixture. Metallic colors are still the rage in the auto industry and pigment manufacturers are seeking to bring to market an expanded palette of organic colors as choices for car designers. Indanthrone Blue fits the industry’s performance niche rather well.


So, Rene Bohn who worked for BASF came up with two “cash-cows” for the company by synthesizing flavanthrone and indanthrone. As far as history is concerned, Bohn is just one of many in a long line of research chemists who toiled in relative obscurity. However, Rene Bohn was not altogether forgotten.


If you happen to be wandering about Germany, a city named Ludwigshafen is south of Frankfort and just over the Rhine River from Mannheim. Websites indicate that Ludwigshafen has virtually nothing to attract tourists. Everything worth seeing is roughly 12 miles away in Heidelberg. However, if you are in Ludwigshafen on business, you can book a hotel room at the BASF Business Hotel Rene Bohn on Rene Bohn Street. Delightfully, BASF did acknowledge Bohn’s contribution and named a hotel after him. How appropriate. Had they named a building in his honor within the operational plant, it would be obscure to most of the public. A hotel’s name is verbalized often, advertised in print, and has both local and visitor traffic. Unless some tribute to Bohn has been located in the lobby or a brochure is in the folder that outlines guest services, it would be safe to assume that few know why its called the Hotel Rene Bohn. But now that you know who he is, you can confidently walk into the Hotel Rene Bohn, head to the dining room, and sit down to a robust meal of roast pork, sauerkraut, and dumplings and regale your traveling companions with stories about flavanthrone and indanthrone.


If Rene Bohn were to come back to life, his assessment of the 1901 inventions of flavanthrone and indanthrone that assisted the BASF corporation to rise to a position of prominence, might cause him to reassess his contribution to the world. Rene, wandering the streets of Ludwigshafen, marveling at the changes to his corporate city, might be heard to mutter, “ I Went to Ludwigshafen and All I Got was this Lousy Hotel Named After Me.”


Syntax of Color

(Edited Essay from 11/2005)

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