Saltpeter is used with Charcoal to create Black Powder, which is used with Cloth to create a Charge in the preparation of Cannons for firing. Prior to Publish 68.3, it was obtained from NPC Alchemists at the Sea Market or at the other docks of the Towns in Trammel and Felucca. As of Publish 68.3, saltpeter is now a gathering resource for miners from niter deposits in dungeons and at sea.
Niter Deposits give saltpeter. When mined they will get smaller and smaller, working their way down through the deposit types until they vanish. The order of deposit sizes, from largest to smallest are:
Niter can only be mined in areas designated as dungeons (Ilshenar is considered a dungeon in this mechanic) or when on a boat. Mining skill and Luck are factors in determining a miner's success at locating niter deposits. Niter deposits can not be picked up. Niter deposits may sometimes spawn within the mountain they are discovered; when this happens, they can be mined by targeting their Context Menu.
For dungeon mining, once an 8x8 area has been checked for saltpeter, it won't be checked again for 5 minutes. In other words, the same location can be checked for niter deposits every 5 minutes, regardless of the success of the previous try.
For boat mining, the chance of finding a deposit is checked for each swing of the pickaxe, but the chance to find a niter deposit and the niter deposit sizes are a lot less than dungeon mining (roughly one third of the chance for dungeon mining). It is reported that a GM Miner with 750 luck has 1.25% chance to find a niter deposit from a boat per mining attempt.