Alchemists' Toybox- Gunpowder; House Rule: Gunpowder and Magic (D&D 5e)

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Any arcane spellcaster who uses a form of gunpowder as a component in a spell or uses a component or focus covered in black powder, intentionally or unintentionally, risks losing control of their magic in a surge of energy. They must succeed on an Intelligence (Arcana) check with a DC of 13 plus the spell’s level or experience a Wild Magic Surge (per the sorcerer Wild Magic ability). If a scroll is strewn with black powder using it forces you to make a Wisdom saving throw or suffer the Wild Magic Surge, in this case results that do not apply result in a Scroll Mishap (DMG 140).

Sprinkling a cartridge worth of gunpowder into a potion, or mixing it with magical dusts or powders, forces a roll on the Potion Miscibility table (DMG 140).

If you have proficiency in the Arcana skill, you can spend a minute and a cartridge worth of gunpowder to detect the presence of magic within 30 feet. Any barrier blocks this effect, but visible creatures or objects that bear magic allow an Intelligence (Arcana) check against DC 13 to determine the school of magic. Doing this does not cause issues with either scrolls or potions.

Next: Gunpowder Weapons

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If we want to add gunpowder to a fantasy world we have to start somewhere. As I said at the outset, most people start from the idea of adding guns to their world and try to work out ways to jam that wholly formed into place. My tack has always been more to worldbuilding. How does the thing fit into the larger structure? How does it distort that larger structure or, and this is the important one for this case, how has the larger structure distorted the development of the thing?

It's well within the realm of reasonable to suggest that gunpowder significantly changed the world. Even beyond the ways in which it remade the face of warfare, the use of gunpowder in blasting and mining and the advances it drove in chemistry are almost incalculable... So, why would it not revolutionize a fantasy world in a similar manner? I started by assuming that gunpowder and magic don't play particularly well together. If magic has already assumed a place of primacy, politically, economically, and functionally (which is true in most modern versions of medieval based fantasy) then it marginalizes the use and interest in gunpowder. However, like virtually any tool, it doesn't foreclose it, as there will always be those who want or need an alternate way.

So, here we have a couple rules which set the tone that magic and gunpowder don't mix well. Based on that, it seemed reasonable that someone (probably some rogue) would figure out how to use that reaction to find magical effects even (especially) without magic of their own. It plays to both the "magic vs gunpowder" theme and starts to build the "alternative but not overwhelming" theme. (These rules are a strictly inferior version of casting Detect Magic as a ritual.)