Thank you, Force! Any suggestions on how to clean it?
As previously stated, a silver cloth should remove the marks if they are tarnish. If not then a silver polish liquid. As for keeping it clean then only regular inspection and cleaning can do that...and beware of leather pouches.
I have investigated my historic problem and can only assume it was the ammonia in the leather that caused the corrosion. The trim being brass based and gold plated should have stood up to a damp environment but if it has a high zinc content then ammonia is a killer.
If I may add here, and as I have mentioned elsewhere, the finish on these pens has changed over the years. Yours will definitely be silver plated but current models are now termed palladium plated. It seems Waterman themselves don't know what to call the plating because they still refer to some as CT (which I assume means Chrome plated Trim) and at least one as ST (Silver plated Trim) yet their descriptions say palladium trim...which should be PT. In itself an odd change because palladium MUST be more expensive than silver.
If I may add to this, attached is a pic of my Case folder with verdigris. It is kept in the Case leather pouch, dry in a kitchen drawer yet always this happens.
Edited by Force, 29 March 2016 - 15:39.