Originally Posted by Camilo

If it's anodized rather than painted (I can't really tell), use Greased Lightening to remove it. I've used it to remove anodizing from a crank and polished it, and it worked very well. I do have a buffing wheel, but hand buffing a couple of clean crank arms wouldn't be a big chore at all.

Look up "remove anodizing with greased lightening" for a lot of printed and youtube instructions. It really is easy and effective. You can get a gallon of the stuff at Home Depot and have enough left over for another dozen or so cranks. If you can find a quart, that would probably do.