I'm not sure where I saw this (on this web site-can't remember which forum) but I tried Tobasco sauce on clad pennies and it worked very good! Pour some on, let sit for 15-20 sec. and rub off.
Whites Surfmaster PI Pro and Whites Surfmaster PI, Minelab Excal NY blue sword. 2 White's Dual field pi, Garrett sea hunter pi II (but don't use it for obvious reasons) 5' x 3 1/2' coil underwater Pi