Englishman Henry Bessemer (1813–1898) was a resourceful tinkerer and inventor, best known for a process for the production of steel. His 1855 patent “Regarding the Production of Malleable Iron by Blowing Air into a Pool of Molten Iron” eventually brought him lasting fame and immense wealth. Along the way, he made many other discoveries. In this part, we will take a look at his breakthrough method to make gold bronze.
3. A Great Discovery: First a Setback, then Golden Treasure
Bessemer continued to tinker and in 1840 he was rewarded for his capability: “My eldest sister, Frances, was a very clever painter in water colours, and enjoyed painting the beautiful tulips that our father lovingly grew. One day she collected together her best flower paintings to present as a gift to our father. On the front of the portfolio she had made to hold them, she wished to have the words ‘STUDIES OF FLOWERS FROM NATURE, BY MISS BESSEMER’ written in bold letters within a wreath of acorns and oak leaves.
The cover of the portfolio was so prettily finished that it struck me as appropriate to use gold lettering. I went to Mr. Clark, a colourman in St. John Street, and asked for his ‘gold powder’. He showed me samples of two colours, and I ordered an ounce of each shade. [In this case, Mr. Bessemer does not use the troy ounce unit typically employed for precious metals (1 ozt = 31.10 g), but the ‘normal’ international avoirdupois ounce (1 oz = 28.35 g)]. As Mr. Clark pointed out, the material was not called ‘gold’, but ‘bronze’ powder.
3.1 Expensive Bronze Powder
When I called to pick up the ‘bronze powder’ on the following day, I was astonished that I would have to pay 7 shillings per ounce for it. On my way home, I could not help asking myself, over and over again, ‘How can this simple metallic powder cost so much money?’ I concluded that it must be made slowly and laboriously by hand. What a splendid opportunity for me to devise a mechanical process for producing this powder. I could earn a fortune.”
Adding sulfuric acid to a sample of the powder quickly revealed to Bessemer that the “bronze powder” contained no gold and was not made of bronze, but brass, an alloy of copper and zinc (CuZn; see Fig. 2). He began to research how this brass powder, which was imported into Great Britain, was produced. For good reason, the production method, which evolved from the traditional gold-beating trade, was kept a profound secret.
Figure 2. About bronze and bronzes. The term bronze has multiple meanings, indicating (from the left): a) Copper-tin alloys (CuSn with > 60 % Cu) and art objects made from them. Henry Moores last bronze sculpture, “Large Divided Oval: Butterfly” (1985-86) at the Kongresshalle in Berlin, Germany, for example; b) All copper alloys with other metals and non-metals with the exception of zinc (brass); c) Fine metal powders (metallic pigments) and paints made with them.
[Images: Left: OTFW Berlin, wikimedia commons, 2016, CC BY‐SA 3.0; Center: www.markimpex.net/bronze‐powders.html; Right: www.bauhaus.info/speziallacke/swingcolor‐goldbronze/p/23754942]
A long search led Bessemer to a clue: “In an old encyclopedia at the British Museum, the powder was described as being made of various copper alloys beaten into thin leaves, after the manner of making gold leaf. The delicate, thin leaves were then ground by hand. This struck me as the most expensive method for producing a metal powder. The use of a steam engine should make it possible to devise a much more effective and inexpensive process.”
3.2 First Secret Experiments
“I erected a two-horsepower steam engine in the back room of my own house, where I could make my experiments in secret. My first idea was to spin a brass disc of about 1 cm in thickness at about 200 rotations per minute and to press it tightly against steel rollers with diagonally grooved surfaces to shave off tiny metal particles.
The machine worked admirably, and minute brass particles were thrown up like a little fountain of yellow dust. But this powder in no way resembled the imported German product. It didn’t shine. I was deeply disappointed at this failure because the promise was so large. The production of powder, worth 60–80 shillings per pound wholesale, from a brass plate costing only ninepence per pound was simply ‘too good to be true’.
Such disappointments are the natural result of trying so many novel schemes. Fortunately, my sanguine temperament soon enabled me to forge this failure and to pursue my usual avocations.”
4. Only a Prepared Mind Recognizes a Happy Accident
“In the field of observation, chance favors only the prepared mind.”
Louis Pasteur (1822–1895)
4.1. The Process
About one year after his failure with the bronze powder, printer Thomas De La Rue incidentally complained to Henry Bessemer about his troubles with underhanded food adulteration. De La Rue had obtained a large amount of arrowroot starch from a London merchant, who had largely adulterated it with cheaper potato starch. The fraud was easily detected by microscopic examination because the grains of starch from potato and arrowroot have different sizes and shapes. Arrowroot starch was highly prized in Victorian Great Britain, because it is a strong thickening agent, forms clear gels, and has hardly any flavor. It is, therefore, particularly suitable for use in marmalade.
“I was struck by this simple detection of adulteration with a microscope. A few days later, it occurred to me to compare my almost forgotten failed bronze powder with the German product under a microscope. A single glance was enough to see the cause of my failure.
The Nürnberg bronze powder consisted of exceedingly thin leaves of brass. When rubbed on a surface, such leaves lie in parallel layers over each other, forming a surface similar to gold leaf, which reflects all light and is highly shiny. My brass particles presented a perfectly different appearance. Under the microscope I found little curled up pieces that arranged themselves without order on a surface, giving a matte appearance.” (see Fig. 3)
Figure 3. The optical appearance of a metal pigment is demonstrated here with a modern aluminum metallic paint. If the metal particles are irregular, scattering light in all directions, the appearance is matte (right). If the metal particles are flat, arraying themselves into a film parallel to the surface, a strong metallic leafing effect (shine) is observed (left).
[Image: FK1954, wikimedia commons, public domain]
Bessemer started over and developed a mechanical production method for bronze powder that consisted of thin leaves.”I believed in the one great success I had so long hoped for. I wiped away all my other pursuits in life, and imagined myself in the lap of luxury, if not of absolute wealth.
In an extension behind my home, to which only I had access, I erected a four-horsepower steam engine and began to develop the other necessary machines. I made most of the machines myself and assembled the whole of it. At last, I switched the machines on with a beating heart and they operated as appointed. The bronze powder was not perfect, but I had proof of the technical feasibility of its production. Commercial success was ensured.”
4.2 Scaling Up
It was now necessary to erect a factory, plan and build many large machines, and find personnel. Such a massive investment would only be feasible if the patent could be adequately protected. To this point, Bessemer had pursued his production process in complete secrecy. A patent application would have the disadvantage that everyone could read the production process published in the patent document and then copy it in secret or abroad. Bessemer and his silent investor and partner James Hadden Young would be powerless to stop this.
After long consideration, they decided not to patent the process for making bronze powder, and to build and operate their factory and machinery in complete secrecy. Still marked by the intellectual theft he suffered at the hands of the British Stamp Office, Bessemer did not trust anyone (see Part 1). He, thus, planned the covert construction and operation of an entire bronze powder factory. The execution proceeded with unbelievable precision and lack of compromise. No intelligence service could have done better.
The biggest problem in implementing this plan was the reliability and incorruptibility of the personnel brought on board. How could Bessemer prevent the disclosure of his operational secrets to the competition in exchange for a year’s salary? Bessemer decided from the beginning to keep the number of employees to a minimum. He would have preferred to do everything himself, but at the very least he trusted his three brothers-in-law—his wife’s three younger brothers—and the machinist who had worked with him for years—an honorable Scot. Only five people, including Bessemer, were involved in the production process. His partner, J. H. Young, his wife, and his young children were not in on the secret. This rigorously reduced number of operators—only five—demanded careful planning of an automated production plant with little tendency toward disruption.
Bessemer took into account potential industrial espionage attempts from the very earliest stages of planning construction of the factory. He searched for a property that was as secluded as possible, as well as being large enough for the factory and a house for his family. He eventually found “Baxter House”, a suitable, remote house with a large property in the St. Pancras section of London.
The big machine house at the core of the factory only had one entrance, which led into a large entry hall. This opened onto other rooms, in which a wide variety of machines would later operate. All rooms could be locked and had no windows. Light came in through skylights, though direct views in through the skylights were blocked by internal shutters. The weight of the machines to be housed in the individual rooms required the floors to be reinforced with concrete or iron plates.
Once the shell of the building was complete, two steam engines were installed in a separate building. After this point, only Bessemer and his three brothers-in-law entered the structure. Bessemer had designed all of the metal-working machines, which were constructed by outside firms. He divided the construction contracts into such small pieces that each delivery would be no heavier than 10–15 hundredweight (500–750 kg), so that it could be moved by five people and no one could determine the purpose of each component. The countless parts contracts were awarded to individual companies, spread across all of Great Britain, keeping each contractor in ignorance of how it all worked.
Delivery of the shipping crates occurred at odd times of the day, and they were left at the entry gate of the property. The rest was carried out by Bessemer and his personnel alone. The components were assembled into complete machines. Once each machine operated to Bessemer’s satisfaction, it was fully covered, so that the function of the machine could not be determined from its appearance.
A total of six different types of machines were required for the production of bronze powder. The steps ranged from turning fine shavings to pressing, polishing, and sorting the particles by size. The full construction and testing of all of the machines took over a year and involved many small changes, adjustments, and optimizations.
After the almost superhuman efforts of everyone involved and the high financial risk, it is understandable that an enthusiastic Bessemer rhapsodized when observing the final step of production: the sorting of the bronze powder according to size in a current of air.
“It is difficult to imagine the beauty of this golden twelve-meter snowdrift, whose appearance changed with every centimeter, from rough pieces that needed further pressing, to extremely fine particles with their silky shine that feel, between the fingers, like pure graphite powder or some other wonderfully smooth lubricant.”
The first order was for two pounds of pale gold bronze for 80 shillings per pound, with a profit margin Bessemer would have considered as “too good to be true” after his initial failure. Further improvements and new product developments were undertaken as production continued.
The factory could process all metals, such as pure copper, to form powders. In addition, the formation of a thin oxide layer allowed for the production of new colors. Many copper alloys were put to the test, including those with bismuth, tungsten, molybdenum, zinc, cadmium, and silver. A silver/copper alloy (1:7) became a particular success because its cream color could be shifted to a deep violet by oxidation. Systematic variation of the oxidation conditions allowed for the constant development of new colors from the many alloys—colors that perfectly suited Victorian tastes.
4.4 Commercial Success
Because of his mechanical production process, Bessemer was able to offer his high-quality products at favorable prices that undercut the competition, which hit the British bronze-powder importers hard. It was no wonder they let him know it: “The sharp competition with the importers was going on pretty fiercely, when one day I received a deputation from the trade. They protested that I was ‘spoiling the business and ruining the trade and myself at the same time.’ I told them that they were laboring under a great mistake: that if I could maintain existing prices, it would make my fortune. They asked, ‘Can you really sell bronze at your present price without absolute loss?’ I replied that I could do so and offered them a discount of 25 % off my wholesale prices if they chose to deal with me instead of importing the powder. At the same time, I would supply no consumer below their retail prices. They accepted my terms and from that time I became exclusively a wholesale manufacturer.”
Bessemer’s inventive mind continued to work to find new outlets for the bronze. He saw clearly that he could produce paints with the shiny powder, which could then be applied to flat or curved surfaces to give them the appearance of metal. He tried to mix the bronze powders with quick-drying turpentine varnishes. However, soon after mixing the metal powder would turn black. He found that this was caused by organic acids in the turpentine. The addition of lime (calcium oxide) neutralized the acids and the resulting insoluble calcium salts could be filtered out. Paints produced with this purified turpentine brought out the shine of bronze powder, and a new “gold paint” was invented.
For Bessemer, this was a commercial success. He sold about 80,000 bottles a year. Bessemer was particularly amused by one particular use. A coffin maker in Birmingham had been using bronze ornaments on the sides of his coffins, but these darkened when stored for long periods. He replaced them with cheaper zinc ornaments, which were given an eternal shine with Bessemers “gold paint.”
The article has been published in German as:
- Sir Henrys geheimer Goldschatz,
Chem. unserer Zeit 2018, 52, 416–425.
and was translated by Caroll Pohl-Ferry.
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