Our kitchen sink is made of cast iron and is covered with, I believe, a white coat of enamel. After a few occasions of over-night dishes left soaking in the sink, rings of rust have developed. It is a double sink and has a rather deep depth which helps make washing dishes a quicker chore. I have not seen this type of sink in any home improvement stores. It is original to the house and I would like to keep it. Is there anything I can do to save the sink?