Removing stains and dirt - Porcelain
Dark stains on porcelain are removed with hydrogen peroxide paste and a non-scratch cleaner. To this mixture is added 1/8 teaspoons (1 ml) acidic potassium tartrate. Apply the paste on the stains, leave for half an hour. Rub with a sponge, rinse.
Greenish stains left by copper utensils are removed with a non-scratch cleaning agent, half and half with sour potassium tartrate, with the addition of hydrogen peroxide (to make a paste). The paste is applied to the stains and left for half an hour, then rinses.
To remove brown stains from old porcelain, it should be soaked in a weak one (5%) bleach solution. Soak for several hours, then wash and rinse. If the stains reappear, repeat the process. Stubborn brown stains on old porcelain are removed with a solution of vinegar half and half with salt.