"After the duel of magic, take out the yellow paper, and say that the demon has already been sealed onto it. Then, when it is ignited, various shapes of demons can be seen."
The operation Xu Yun described was actually a very common 'exorcism' method during the Ming Dynasty.
Because according to technological development, the core material needed for the entire process... that is, potassium nitrate solution, would only start to become relatively common by then.
Of course.
Back then, Daoists didn't call it potassium nitrate solution; they called it yellow nitrate water.
The Song Dynasty hasn't developed to this point yet, but Xu Yun had already produced potassium nitrate while preparing the salt bridge and nickel steel,
with the help of this super-dimensional solution, it's extremely easy to feign the mysterious, and ensures that no anomalies are discovered.
As for Old Su's mention of retrieving items from boiling oil and burning ghost corpses...
