[Millennium]

I wonder: they mention that the powder can ignite prematurely when you place the top anvil. Could you prevent that by putting a piece of paper between the anvils? It seems to me that the paper should prevent sparks by preventing direct contact between the anvils, but be weak enough that it shouldn't affect the deflagration too much.

Then again, I'm not an expert in this kind of thing. Would this somehow make things way more dangerous in a different way?

[snazz]

I’m not an expert either but I would have guessed that the force from the top anvil acts like a hammer and detonates the gunpowder that way instead of with sparks.

[larkeith]

They mention using a playing card between the anvils in the article, and in at least one [1] video they seem to use paper between the anvils as well, so it seems probable it would work - or at least not hurt.

[1] https://youtube.com/watch?v=S8HbhiRlgM0