The most convenient and abundant source seemed to be refining it directly from saltpeter mines.
But in the beginning, the Daoists certainly didn't obtain saltpeter this way.
After all, this stuff was a byproduct of Daoist Alchemy.
The Daoists' Alchemy Dao was really just an attempt to use refining methods to extract the essence of the world, then consume it for their own benefit.
It was understandable that they would call saltpeter the North Emperor's Profound Pearl.
They probably saw the beautiful, crystalline substance forming on the surface of caves.
Those guys must have thought it was a condensation of Heaven and Earth Spiritual Qi, which is why they used it for Alchemy.
If the materials for Alchemy came from latrines or pigsties, the Daoists probably wouldn't have been able to stomach the Elixirs.
The mere sight would have made them vomit, let alone try to refine it.
"Elder Physician! You've already accepted my silver notes for ten thousand taels of silver."
