I have a 1974 steel French road frame and most of the original paint is still intact. However, there’re quite many 1-2 cm surface rust spots. I also recently had one of the lugs partly re-brazed and the guy who did it removed most of the paint around the lug. How can I treat the rust spots and that area where the paint was removed without repainting the whole frame? What solutions can I cover only those specific spots with after removing the rust from them to prevent rusting (if possible, without using paint – I kind of like the look of frames with places where bare frame is seen)?
I would lightly rub the offending area with steel wool. The idea is to not completely remove the rust but to dislodge any paint that is intact but not bonded to the metal. Apply a rust restorer or converter. Rustoleum is one brand but there are many others. Apply the converter to the prepped areas per the instructions. The chemical process converts the rust and leaves a coating on the bare steel(typically black). You can then cover the areas with either touch up paint or nail polish of a similar color. If you visit a Hobby Shop they have small bottles of enamel paint that you could custom blend to get a close match.