In the early modern period, saltpetre was perhaps best known for its role as one of the three components of gunpowder. For natural philosophers in seventeenth-century England, saltpetre also had important uses in chymistry and medicine. While some factories did successfully produce saltpetre in early modern England, the domestic industry was not on the whole a great success. Intellectuals who were keen to apply their knowledge in the real world saw this as an opportunity, and proposed a variety of new and improved methods that they claimed would produce this vital material more efficiently and in abundance. Yet their proposals remained on the page and their efforts fell flat. To understand the challenges and experiences faced by both scholars and artisan saltpetre-makers, I 'reworked' early modern methods of saltpetre-making with the Medieval Gunpowder Research Group. Reworking revealed procedural challenges and complexities that explain why, even with the best intentions, seventeenth-century natural philosophers struggled to get to grips with this important material.