Well, this is something totally new for me. But my friend, Dee, offered to show me how she does this. I know many people do "scratchboard". But Dee does her on aluminum. The scratched out areas shine with a silver gleam! Very fun!
You can use any sharp tool...she uses one of those craft knives. My friend, Peg, uses a roofing nail put through a cork. This allows her a more comfortable "handle" to scratch with. Works great!. This is 8 x 10 (black spray paint on aluminum flashing). I used a photo I found in a magazine and you can trace it on using white carbon paper.
We worked on this about two hours.