Hi, I've bought a ring in a second hand shop (good price) but when at home, have noticed a stain. It's on the outside and really annoying - I think the shop lighting was dim so I haven't noticed.
It looks like a testing acid stain as it's dark-ish copperish colour and has the petrol style rainbow effect. Worried that it's not a testing acid though but something corrosive - and that's why the price was good?
Have soaked in fairy liquid and then also tried rubbing with baking soda as advised, but not change! It's next to a small stone so need to use something that won't dull the stone too!
Grateful for advice!