How to remove copper stains from Gold panda coins

[Paul]

This video seems to show it doing a half decent job by simply using a storm-lighter on affected areas.

Anyone who wishes to have a dabble with affected coins, feel free to report back here their success or failures with using this technique

[Pete]

Perhaps dipping in nitric acid would attack / remove the copper film but leaving the gold untouched ?
Only aqua-regia will dissolve gold so should be safe.

After watching this video it did seem to work pretty well but it could be high risk on a proof coin and often when metal is overheated it develops a bloom which would easily be picked up under the right lighting conditions.