Saltpeter
Saltpeter is used with Charcoal to create Blackpowder, which is used with Cloth to create a Charge in the preparation of Cannons for firing.
Saltpeter may be obtained from NPC Alchemists in Sea Market for 32 gold each. It is not craftable by players, but historically derived from grinding manure with wood ashes and soaking in urine as a component of gunpowder.