I had a 4700uF-35v capacitor that I connected in parallel with about 18v. I would short it over some aluminum foil and being that it was connected in parallel, each slight disconnection with the foil would result in a recharge. Probably not worth mentioning, I definitely saw some sparks. The foil would actually deteriorate (holes would be made.) My question is, what exactly is happening to the aluminum? And what "are" these sparks that are being seen? Also, do I need to take safety precautions when doing this (other than the needed precaution for the possibility that the capacitor may explode if not handled properly)?