Why not just wave your wave and recite the right spell?
The only hint is that a couple of potions appear to be unduplicatable -- there are no spells to give luck, or to force people to tell the truth.
It could stand to be a bit better defined. Especially since the spells are all quick to cast, meaning that you get no time advantage from just chugging a potion. Perhaps the potion could last longer. Perhaps casting times could sometimes be longer. Perhaps it's a lot easier to do magic with stuff because you can get the laws of sympathy and contagion on your side. Perhaps some types of magic can't be done without such an embodiment.
Something I'm going to have to define harder, when I've already defined a character as the son of a merchant of stuff you use in magic, and made another plot element revolve about stuff.
