Major problem: My husband accidentally left a Mauviel sauce pan with water on the burner and fell asleep... the water boiled out and now there are black-ish circular stains on the inside of the pot which will not come out. I am pretty sure that the pots are stainless steel lined (silver colored rivets with brass handles). He bought them about 10 years ago. I tried removing the spots with Barkeeper's Friend, and I think that they got a little lighter. Is the pan ruined?