How do I fix my copper Ruffoni fondue pot that has changed color with heat? ?

I think I forgot to add water to the pot before heating it and adding the insert. This happened the first time I used it and it still has rainbow like colors on it. I have found all sorts of websites telling you how to create this effect but none to rectify the problem.How do I fix my copper Ruffoni fondue pot that has changed color with heat? ?
Bar Keepers Friend.



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All the walmarts have it.



Cameo is better for very delicate things... not as harsh as bar keeps friend, but takes a lot more work getting things clean:



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