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What Nikolas calls 'gold' is just clear lacquer with a gold tint. It will not make silver parts look like brass. It was designed as a feeble attempt at touching up the old 'Eastlake gold/orange' lacquer.

At best, Nikolas is formulated to use as a touch-up and doesn't have near the durability of factory lacquer.

You're not likely to hurt nickel with any kind of spray-on finish. Finishes out of a 'rattle can' are not likely to stick to nickel very well, either.

Nice jobs on the cars, guitars, etc.

As already stated, the gold stuff is lightly tinted clear lacquer.

It takes a good four to five coats to get a proper gold tint going and if there are any runs the tinting makes any unevenness all the more obvious.

In addition, the gold tinting is just plain ugly.

If you do a proper polish and degrease the clear stuff sprayed liberally can do an admirable job of protecting your horn.

I well equipped brass overhaul shop will have a proper spray booth and oven for applying the baked epoxy lacquer used in factory settings if you have your heart set on the most durable option.