I touched up the black on my Sr Semi Pro with model paint with good results. One thing I would recommend is to mask off the frame around the chip/ scratch as closely as you can to the affected area using 3m blue tape. Then when you sand down the rusted ares you won't sand a larger area than necessary. I like to sand , then put a dab of naval jelly on the spot to clean off the rust/ follow with a rust inhibitive primer ( Rustoleum) then color with paint brushed on with a fine artists brush . Pull the tape off then re tape back about a quarter inch and then wet sand the patch with 1000 grit wet and dry paper. Let dry thoroughly. Remove the tape and go over area with white polishing compound applied lightly and see how it looks. With a black frame it should pass the 3 ft test.