The Chinese invention of gunpowder did not occur overnight. In China, the primary ingredients of gunpowder, sulphur and saltpeter, had been commonly used for centuries as components for medicine. It's no surprise that eventually Chinese alchemists, in their search for concocting new medical elixirs, were able to combine the two and stumble upon gunpowder. In fact, the Chinese term for gunpowder, huoyao (火藥), can be literally translated to "fire drug". The oldest recipe for gunpowder is the one in The Collection of the Most Important Military Techniques, a Chinese text from the 11th century.

In the West, there is no evidence that Byzantines had access to refined saltpeter prior to the 12th century. The Byzantines did have Greek fire, an early incendiary weapon likely manufactured from petroleum. Petroleum, an ingredient in abundant supply near the Mediterranean, could have been distilled and thickened with resins, creating a flammable liquid roughly similar to modern kerosene.

A History of Greek Fire and Gunpowder by J.R. Partington

Firearms: A Global History to 1700 by Kenneth Chase