I have some very, very old blue, and less old flame, Le Creuset. I have been pretty good about washing it by hand but occasionally it has made it through the dishwasher. In addition, we live in an area with very, very hard water. As a result, most of my Le Creuset has nasty white stains on the outside that I can't get off. Sometimes I oil the exterior, and that polishes it but only temporarily. Does anyone have suggestions? Thanks!