Many French horns, for example, are made of nickel silver, an alloy of copper, zinc, and nickel (it's silver in name and color only), and some are made of nickel bronze, an alloy of copper, tin, and nickel. (Brass itself is an alloy of copper and zinc.) Many brass instruments are silver-plated (sterling silver on brass), and some are gold-plated.

NPR: Young Tuba Player Gets Nod from Phila. Orchestra