Making gunpowder is a bit like cooking, except more explosive. Manufacturers of gunpowder in the 14th and 15th centuries used black powder imported from China to Europe and then mixed its three ingredients one by one: saltpeter (also known as potassium nitrate), charcoal, and sulfur. But they also did a few chef improvisations, including a touch of brandy, vinegar, or varnish.
Now, a group of experts from the US Army Military Academy at West Point have recreated these medieval recipes and tested the handcrafted gunpowder in a cannon replica. They found that early gunpowder took a lot of experimentation to be successful, and it gives them insight into how modern bomb-makers might use similar trial-and-error methods to assemble explosive devices. .
The project began when West Point history teacher Cliff Rogers was walking the Feuerwerkbuch (German for “fireworks book”), a collection of anonymous manuscripts. Rogers says the Feuerwerkbuch is a practical manual for master gunners, explaining how to process the ingredients of gunpowder, how to prepare it, and how to load and fire a cannon. The manuscripts were assembled over several decades as gunpowder and artillery technology changed rapidly; the book included recipes from the year 1336 to its publication in 1420 and used descriptive terms such as “common”, “better” and “even better” to describe the combustion properties of each mixture.
Rogers asked his colleague Dawn Riegner, a chemistry professor, to verify the facts of a recipe that included an unusual ratio of sulfur, saltpetre, and charcoal. “The main objective was to verify the interpretation of a particular recipe that seemed wrong,” says Riegner, who was the lead author of the team’s article, published this month in the journal. ACS Omega. The problem turned out to be a translation error, not scientific, but which had sparked their interest. “Then it was: Well, what about all these other ingredients that medieval gunners put in, and what was the thought process? Said Riegner. “Did these people who don’t have a chemistry degree know what they were doing?” Did they have a guess as to what these new ingredients would do for them, or how mixing them together would help them?
Riegner and Rogers decided to recreate these early recipes and find out if they would still work. Riegner worked in his chemistry lab with his daughter, an undergraduate 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, starting the dry mixes together,” she recalls. “And then, if necessary, when it was expressed in the recipe, we would also add different wet solutions, whether it was water, varnish or vinegar.”
Once the final product was obtained, the mother-daughter team placed the material in a chamber containing pure oxygen to test the “bomb calorimetry” of the gunpowder, which is a measure of the amount of thermal energy produced by its ignition.
Riegner says that part of the project encountered some obstacles. The ingredients used in the lab were of scientific grade meaning they were extremely pure. But the sulfur and potassium nitrate used in the 14th and 15th centuries would have been more contaminated. Perhaps this is one of the reasons the gunpowder cooks added extra ingredients. The team found that over time, recipes began to use greater amounts of sulfur in order to replace the more expensive saltpeter, which was difficult to obtain. The sulfur had to be purified, hence the use of other additives, says Riegner.
They could also have been used to turn the dry ingredients into a wet paste which was then dried and purified into gunpowder. And there is a third theory: researchers believe that the alcohol in brandy could also have supplemented the organic compounds in the charcoal of the first gunners and improved its combustion. But modern experience has not been able to accurately determine the effects of these additives, as researchers start with better quality ingredients. “None of them have really improved the energetics,” says Riegner.