I have a china trumpet that is silver plate. The china horn was reworked by my fav tech that also designed the horn. The horn was cheap but not as bad like most china horns are. I bought on close out just to learn to play trumpet.

So if you let a silver plated horn tarnish a lot, will it hurt the metal under the plating? Or will it be just like an unlacquered horn that just looks tarnished?

tarnish is only on the silver plate, and it is very easy to get off with any silver polishing method. If you don't want to polish it, let it tarnish.

I will let it tarnish.

Besides. A trumpet should be the black sheep of the horns.