Mum has an old-fashioned chain for her glasses. It is made of copper wire and seed-pearls. She thought she would wear it and got it out of the box, only to find the copper has turned green. A quick Google has suggested mild acid...lemon juice, vinegar, ketchup et.c ....but not with seed pearls. So, anyone got ideas on how to clean this chain so Mum can wear it again?