making gunpowder A bit like cooking, except for the explosives. Gunpowder makers of the 14th and 15th centuries used black powder brought to Europe from China, and then mixed its three ingredients one by one: rock salt (also known as potassium nitrate), charcoal and sulfur. But they also did some chef-like improvisations, including spraying brandy, vinegar, or varnish.
Now a group of experts at the US Army Military Academy at West Point have reinvented these medieval recipes and tested artisanal gunpowder in a replica cannon. They found that the early use of gunpowder took a lot of experimentation to get it right – this gives them insight into how modern-day bomb-makers use similar trial-and-error methods to assemble explosive devices.
The project began when West Point professor of history, Cliff Rogers, was researching a file fireworks book (German word meaning “book of fireworks”), a collection of anonymous manuscripts. Rogers says the Feuerwerkbuch is a practical handbook for artillery masters, discussing how gunpowder components are processed, how to make it, and how to load and fire the cannon. The manuscripts were compiled over several decades when gunpowder and artillery technology was changing rapidly. The book included recipes from 1336 until its publication in 1420 and used descriptive terms such as “common”, “better” and “still better” to describe the combustion properties of each mixture.
Rogers asked his colleague Don Regner, a professor of chemistry, to validate a recipe that included an unusual proportion of sulfur, rock salt and charcoal. “The main goal was to verify the interpretation of a particular recipe that seemed wrong,” says Regner, who was lead author on the team’s paper, which was published this month in the journal. Omega AC. This case turned out to be a translation error, not a scientific one, but that piqued their interest. “And then it became: Well, what about all these other components that medieval gunners were putting in, and what’s the thought process?” Regner says. “Do these people without chemistry degrees know what they were doing? Did they have a hypothesis about what these new ingredients would do for them, or how mixing it would help them?”
Riegner and Rogers decided to recreate these early recipes and see if they would still work. Regner worked in her chemistry lab with her daughter, an engineering student at Stevens Institute of Technology, who was at home during the Covid-19 pandemic last year. “We started mixing the ingredients in the lab, and starting the dry mixes together,” she recalls. “And then, as needed, when expressed in the recipe, we also add various wet solutions, whether aqueous, varnish or vinegar.”
Once they came up with a final product, the mother-daughter team put the substance into a chamber containing pure oxygen to test the “bomb thermometry” of gunpowder, a measure of the amount of heat energy produced by its ignition.
Regner says this part of the project ran into some snags. The ingredients used in the lab were of scientific quality, meaning they were extremely pure. But the sulfur and potassium nitrate used in the 14th and 15th centuries were more polluted. This may have been one reason chefs added gunpowder for additional ingredients—the team found that over time, recipes began using more sulfur to replace more expensive, hard-to-obtain rock salt. Regner says the sulfur needs to be purified, which is where other additives are used.
They may also have been used to turn dry ingredients into a wet paste that was later dried and refined into gunpowder. A third theory: Researchers believe that the alcohol in brandy may also be complementary to the organic compounds in early artillery charcoal and its good combustion. But recent experience has not been able to accurately determine the effects of these additives, because the researchers started with high-quality ingredients. “None of them really improved on energetics,” says Regner.