TromboneChat

I bought a King 3BF from the 70s. Great horn, but it looks like at some point in its history someone cleaned the bell with something abrasive, so it's got very fine scratches over most of the bell where they rubbed it. The lacquer is mostly intact, so is there anything that can repair scratches in lacquer?

Not really, no. If you must have a uniform appearance on the instrument, you can strip the rest of the lacquer. This process comes with its own challenges and is best left to a professional.

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You can't "repair" lacquer. You can re-lacquer. Those are your choices.