Summary There would be no guns without gunpowder, the volatile mixture of saltpetre (potassium nitrate), charcoal and sulphur that came to Europe in the 14th century. Chinese chemists were experimenting with early forms of gunpowder by the 9th century or even earlier. Mixing gunpowder was a tricky procedure largely carried out by hand under the constant threat of accidental explosions. Gunpowder production was as dirty as it was dangerous. To make saltpetre, workers mixed rotting vegetable waste and animal (or human!) excreta together in large beds and waited for nitrates to form as a white powder, which was later refined.

• Documentary