Another use I had forgotten. Several years ago three 7x17 framed pictures came back from a group show. The frames were Nielsen black aluminum. The show must have used volunteer labor from prisoners who normally stamped out license plates. Each frame piece had scratches and scrapes. They were a mess and unusable for any future show. I inquired here or the LF Forum and several members suggested magic marker or sharpie pen. I tried and the frames looked almost new again.