TromboneChat

I have a gold plated 3BSS that was shining when I bought it second-hand about four years ago. In the meantime, it has tarnished in many smaller spots, but also in some larger blotches. In a way it resembles tarnished silver.
What can I do to get it clean again without ruining the gold plating?

Thank you for any informed advice!

Do you know who did the gold plating? It is necessary to plate with nickel before gold, in order to prevent the base metal(s) (copper, zinc, silver, ect) from diffusing into the gold plating layer and tarnishing themselves. In addition, if the gold layer is not thick enough, it will be porous, and air can reach the underlying metal to tarnish it.

There needs to be a barrier layer between the brass and the gold.

Some manufacturers use a silver layer and some use a gold "strike" layer. While we used to use nickel in electronics, nickel is more brittle than the brass or gold and will tend to flake.

A proper plater will remove the old plating first, then buff, add the barrier layer, and then the gold.

For something like a mouthpiece I'd want a thicker layer than appearance color; at least 25 micro-inches (about 0.6 micron).

Sounds like it was gold plated at the factory and lacquered with King epoxy lacquer. Then the lacquer gets a small nick which allows moisture to get underneath. I saw it a lot with silversonics.