I probably shouldn't say gunpowder more of an explosive powder. But if had to guess as to how that'd be done perhaps grinding it down to like a paste using an organic binder than adding some sort of liquid. Could then become a kind of sludge. If you prefer I could remove it, I only had it to give a certain "realistic magic" to the character. Kind of like the Immortals from 300 how they had their version of impact grenades which were considered "sorcery".