Stains on Porcelain
If your pipes carry hard water (which contains minerals such as limestone, calcium and magnesium), it may leave a thin film of white powder or an orange rust stain on the surface of sinks or tubs. Smallin's fix is to buy a pumice stick from a hardware store. Wet the surface of the sink and the stick. Then, gently scrub away the stain. Be careful not to scrub too hard to avoid scratching the porcelain. A paste will develop, which will help clean and polish the porcelain. Once the stain is gone, rinse the basin clean.