Not sure why I never caught this but it appears there’s yet another unanswered question JK Rowling left us in the Harry Potter books: What can’t a wizard create out of thin air? Hermione tells us one thing, but we are told there are five. Author Tere Stouffer takes a stab at an explanation of Gamp’s Law of Elemental Transfiguration in The Complete Idiot’s Guide ® to The World of Harry Potter.
In Deathly Hallows, J.K. Rowling reveals only one exception to the law: Food.
Hermione says, “It’s impossible to make good food out of nothing! You
can Summon it if you know where it is, you can transform it, you can increase
the quantity if you’ve already got some.’” And that pretty much sums up what we
know about Gamp’s Law and its five exceptions.
But what else can’t be conjured or transfigured?
– Money and Shelter: This is two items, but they are often inextricably linked: one can’t have a beautiful or large home without having money to pay for it. Although an interior of a room or area can be expanded, as the Weasleys did while camping at the Quidditch World Cup and while riding ministry-borrowed cars, and valuable objects can be multiplied, if the intention is to suffocate a thief inside a vault at Gringott’s, they can’t be created from scratch.
– Clothing: Even wizards of great skill—Remus Lupin and Molly Weasley included—cannot seem to conjure up new robes and are instead stuck with old, patched ones, ones that are too short, or ones that are hopelessly out of style. If clothing were not one of the exceptions, Lupin would have long ago conjured a new wardrobe, and Ron would have avoided his dress-robe embarrassment at the Yule Ball.
– Body Part Removed by Dark Magic: In the wizarding world, all sorts of body parts can be repaired and even conjured from scratch (like the regrowing of Harry’s bones after his quidditch accident in The Chamber of Secrets.) But these same body parts—and the entire body, in the case of the Killing Curse—cannot be replaced or repaired if Dark Magic was involved, no matter how skilled the healer.
– Temperature: The conjuring of heat or cold or the transfiguring of something warm into something cold (and vice versa). Although wizards can produce water (Aguamenti!) and can emit steam from their wands through the hot-air charm—steam that lightly melts objects like snow or dries objects like sopping-wet clothing—wizards cannot raise or lower the temperature of the air, stop rain or snow from falling, slow or speed the wind, or heat or cool large bodies of water.