you could also just look for sand paper labeled as wet/dry sanding. It will either be garnet or silicone dioxide. Both will work equally as well. The wet/dry just means that they use waterproof glue and paper that stays strong when its wet. Try to find something thats somewhere between 100 and 180 grit. Any coarser (lower number) and youll end up sanding away more of the rotor than you need to. Any finer and it will just take forever.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson