Normally hardware used on musical instruments is either machined, cast or fabricated with some material suitable and plated either to cover up the cosmetic appearance of the bare or raw material or plated for longer durability. Many pole pieces are in their natural cast state and are not plated and as the instrument is played and in contact with hand sweat, abuse and constant plucking of a pick on the hardware the protective coatings can wear down. Most plating materials used do not withstand long use especially when subjected to nightly sweat, humidity, dings, wear from hands and other foreign objects.

I’ve seen players rehearsing all afternoon in 95% humidity with their instrument case left open to absorb the moisture all day. After practice or performing they expose the instrument to high amounts of humidity after the case is closed. The air and especially the glues in the case can break down the finish and hardware after a short amount of time. You need to use protective measurements to help reduce the moisture in your case and wipe down your instrument after a performance or handling. This will get the get the fingerprints and smudges of the instrument to help reduce the finish from becoming dull or tarnished.