try using a magic eraser
Lemi-Shine, you find it with dishwasher stuff at the store, get the dishwasher booster not cleaner. I use it in the dishwasher and it has removed all the hard water deposits from the bottoms of coffee cups and bowls but I think if you would run a sink of very hot water with it added and then let the dishes soak for a good while it would still work. I do that with my electric kettle when the element gets a coating of lime on it and after 2 or 3 hours the element is as shiny as new again. I also use it to clean the coffee maker, love the stuff for hard water stains!The undersides of my dishes plates bowls ect have a brownish stain around the round foot. Dont know how what. I hand wash with well water. Any ideas on cleaning. I tried scrubbing with dawn but nothing.