...Use a small "art" brush for touch-ups?
What kind of paint should I use?:dunno:
If you want to try for a more permanent solution, then use an art brush (size appropriate for scratch width) with plain black enamel. Depending on your skill, that can give you a satisfactory result. Just try to keep the touch-up paint inside the scratch; get sloppy, and excess build-up on the sides of the scratch will make the repair look amateurish. This repair, depending on your skill, can also be invisible from about three feet.
Lowes or HD sells a Rustoleum enamel in half-pint cans. It comes in flat black or high gloss black; chose which works better on your wheel finish. I used this product to paint the spoke pockets on some old "Hurricane" style wheels I had after using an acid-based cleaner (wheels not clear-coated). Normally, this would be a tedious, thin-coat process with spray paint and masking. The brush-on approach gave a superior, high-thickness coat with outstanding appearance; in a warm area, the brush marks will tend to "flow-out" to a fairly smooth finish.
I simply cleaned the wheels with the cleaner, allowed the surfaces to dry thoroughly, then painted the enamel. I then carefully cleaned any "goofs" off the spoke faces with lacquer thinner on paper towels. That process gave me a much sharper line than ever possible by masking.
Cleaning with lacquer thinner shouldn't be necessary for your "touch-up", just keep the paint "inside the lines". In fact, use of lacquer thinner IS NOT recommended for your application; you might end up with a larger "dulling" problem that you'll need to fix.
