Choosing a Tuba
Key Points for Choosing a Tuba

Because the timbre of a brass instrument is determined by the way that air vibrates in the air column, the materials used to make the instrument, in addition its shape and length, will have a slight effect on the timbre.
For many years, brass has been the traditional material used to make these instruments. Brass is more malleable (easy to work with) and corrosion resistant than iron or other metals, and since it is also pleasing to the eye, it is well suited for the bodies of brass instruments-brass is what gives the brass instruments their characteristic tone.
Brass is an alloy of copper and zinc, and the differing composition ratios of the brass used in tubas and other brass instruments give rise to their variations in timbre.

Finished metal tubes are filed and sanded to make their surface smooth as glass, and then they are coated with a polish and buffed with a high-speed buffer to give them that beautiful metallic shine. At last the stage, lacquer or plating is applied.
The primary purpose for the lacquer or plating is to protect the metal from rust and dirt, but it also has a slight effect on the timbre of the instrument.