One large point of controversy has always existed between those who prefer a lacquered horn and those who prefer plated horns, either silver or gold, or a third group who prefer their instruments in plain brass without any protective coating whatsoever. Let me give you my findings on the three different finishes of instruments. First, I tried to find myself three instruments that played absolutely identically. One, I silverplated, one I had a very good lacquer job put on and a third I left in brass. Now recall that all three instruments played identically the same in brass, or as close as it is possible to get. I had various players from the Symphony working with me as well as other professional trumpet players in Chicago and they agreed unanimously on the results. The findings were that plating does not affect the playing qualities of brass instruments. That is, the plated instrument and the plain brass instrument played identically. The lacquered instrument, however, seemed to be changed considerably. This instrument, which originally had played the same as the other two, now had a very much impaired tonal quality and the over-all pitch was changed.
To explain these findings as to why the silver and brass instruments played alike and the lacquered instrument did not, let me give you some figures. The silver plating on a brass instrument is only one-half of a thousandth inch thick. In other words .0005 inch. The lacquer that goes on, if it is a good lacquer job, is approximately seven thousandths of an inch thick, or .007 inch. Now to get an idea in your minds as to what these thickness figures represent, an ordinary piece of writing paper is approximately four thousandths of an inch thick so the silver that goes on an instrument is only 1/8 as thick as a piece of writing paper, while the lacquer is almost double the thickness of a piece of writing paper. The silver in itself is very compatible to the brass. The lacquer, if it is a good lacquer and baked on, will be almost as hard as glass and not at all compatible to brass. The lacquer on the bell of an instrument is seven thousandths of an inch thick on the outside and another seven thousandths on the inside which gives you a total thickness of fourteen thousandths or .014 inch. This is already the thickness of the metal of my instruments so the lacquer process would double the bell thickness. As you can see, it is bound to affect the playing quality of the instrument.
from - The Schilke Brass Clinic