I wonder if a copper sulphate solution would be sufficient to *restore* the thin copper coating on mig wire?!?! I remember using it for layout work, way back in the day.... a clean steel object could be given a thin copper coat by simply wiping it with a copper sulphate solution and I recall it took a fair bit of elbow grease to get the dang stuff off after doing the work.
As for using "*clear* polyurethene lacquer"..... uhh, I think you *might* be getting your coatings mixed up. Lacquer and polyurethane are 2 different beasts... I suspect you were referring to polyurethane coatings, and that still leaves us with the question of waterborne or oil-based... My preference would be for the latter as I think it would have a better chance of a complete seal, but multiple layers would be required and spray or wipe applications would need to occur about once an hour... Wait too long and the second coat would not adhere to the first, too soon and you wash the first coat off.
Lacquer would be great for antennas. No need to worry about the solvent and what it might dissolve, in which case I would just buy a small bottle of clear acrylic nail polish, it even comes with a brush!
Lacquers and nail polishes which are in the same category can be re-dissolved with lacquer thinner, acetone and the like (sure, why not.... nail polish remover too). The only problem with brushing lacquers is that the solvent in your second coat begins to melt the first coat, so you have to be quick and yet careful.
Polyurethanes are a one way deal, once the cross-linking is complete, it cannot be dissolved by it's original thinner and must be mechanically removed. And it is for this reason that additional coats must be applied within a short window of time... You need to wait for the cross-linking to start and firm up the first coat, but you need to apply the next coat before the first coat finishes cross-linking so the two coats can link together. Yes you can mechanically abrade a coat that has fully cross linked so the next coat can *key* into it, but it is not as strong a link and imperfect prep would lead to failure of the protection one was seeking.
Regards
Christian