Does anyone know how I could remove metal marks -- the kind of marks someone being really careless (me) makes when putting something with a metal rivet in it on the edge of a s/n print? I didn't realize that the rivet was on the print until it was too late, and now there are a bunch of little marks along the edge. The print itself is kind of spooky. It is a pencil drawing done in 1993 of the NYC skyline & there are two helicopters in the sky and a plane right on the side of one of the WTC towers. It's eerie.