Another thought is that perhaps consuming something transfigured is a Bad Idea.
If the effect is temporary, I can certainly see why it would be a very bad idea, indeed. That nice piece of chocolate cake you've just eaten might turn back into a rock while you're half-way through digesting it.
That would explain why we have to have a Potions class, which would make little sense if you could just haul out your wand and change water to wine, or more to the point, to Polyjuice, or Wolfsbane, or Veritaserum.
I'm not sure that would be possible anyway, regardless of duration. I don't think we've ever seen an example of a non-magical item transfigured into a magical item. I would guess that you couldn't transform a chair into, say, a foe-glass. You'd have to transform it into an ordinary mirror, then put the foe-glass charm on it yourself. If you tried changing water into Wolfsbane, I suspect you'd end up with something that looks and smells and tastes like Wolfsbane, but doesn't actually do any good for the werewolf who drinks it.
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If the effect is temporary, I can certainly see why it would be a very bad idea, indeed. That nice piece of chocolate cake you've just eaten might turn back into a rock while you're half-way through digesting it.
That would explain why we have to have a Potions class, which would make little sense if you could just haul out your wand and change water to wine, or more to the point, to Polyjuice, or Wolfsbane, or Veritaserum.
I'm not sure that would be possible anyway, regardless of duration. I don't think we've ever seen an example of a non-magical item transfigured into a magical item. I would guess that you couldn't transform a chair into, say, a foe-glass. You'd have to transform it into an ordinary mirror, then put the foe-glass charm on it yourself. If you tried changing water into Wolfsbane, I suspect you'd end up with something that looks and smells and tastes like Wolfsbane, but doesn't actually do any good for the werewolf who drinks it.