Depends on what exactly your magic can do. Rust happens when iron is exposed to air and water for long periods of time. If you can conjure up air and water you can expose iron to them, but it wouldn't make the iron rust any faster than normal.
If you somehow had control over the atomic structure of objects you could probably force a piece of iron to become rust, but at that point you'd also be a living god.
They should have sent a poet.As far as I know, oxidation of metals is proportional to the surface area exposed to oxygen (and the temperature, as noted above). I'm not sure if moving oxygen past the metal faster (as with blowing air or moving water) would affect this rate noticeably. However, abrading the surface of the metal (with carried dust particles), or corroding it (with salt or other dissolved substances), would most definitely increase the exposed surface area and hence the oxidation rate.
edited 29th May '18 5:44:40 AM by Fighteer
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

So we have say... wind or water magic(the ability to manipulate wind or water). Is it possible to use these fabulous powers to speed up the rusting process of metals? And if so, to what degree do you suspect?
What does signature do?