On a fallen world that still has firearms. Society is still advanced in a way, but is more tribal/feudal in nature. There is an armed priesthood that preaches and deals in death. To the unbelievers they are called the Powder-Priests or Death-dealers, to their followers they are called (haven't given them a cool name yet). The Priesthood forever walks the towns, villages and battle fields in search of new bodies to add to the pile, for you see they believe that in battle Death must come from Death itself. They are under the impression that items containing remains of the dead become beacons for it; that when it enters the body life will fade. They take the bodies to the powder fields found close to all towns (think graveyards except the bodies are out in the open) to make what they call the essence of death; it is what you would call gunpowder. The Priests sell the powder to all factions in the world believing that they will be the cause of their own destruction, the other factions take the powder not caring either way.
The idea is that the Powder-Priests have these powder fields filled with bodies, so that they can make gunpowder. I read a book from Japan about the Sengoku period and a group that did this (I think they were monks) and thought that it would be cool to use this in my own book but the book that had the info has been lost and I’m having trouble getting the right way on how they did it. I think it's bodies, urine, and charcoal and leave it for a few years? (I tried looking it up; swear I’m on someone’s watch list now.) But I have no idea what the technique is or that I have the right… ingredients.
The Question: How to make Gunpowder out of Corpses?
This one was a little bit on the odd side for me to ask, but if it helps me make a better book I’m fine with it (hears knock on door FBI opens up). I know that the book I read was based on real events and I have also read somewhere else about this being done before (or something similar)... I think the French? I’m also aware that there are better ways of making gunpowder, but this way fits perfectly with the group and their ideals, so I think I won’t change it.