Mix water with cream of tartar
Boil a little amount of water. You can now fill a tablespoon and mix it with ¼ cup of cream of tartar.
Blend the mixture
Grab a spoon which can be used for mixing. Now blend water and cream of tartar nicely for a few minutes or until it turns into a paste.
Scrub the porcelain sink
Take a clean sponge and make it wet before dabbing it in the paste. You can now scrub the surface and the walls of your porcelain sink. Keep in mind that you may have to use hard hands or apply additional pressure if the sink is very dirty or possesses a few spots and shades. Continue to scrub the surface until it gleams.
If you are unable to remove any spot or stain, apply more paste on it and scrub that portion of your porcelain sink harder.
Rinse the surface
You can now wash your porcelain sink with warm water and it should shine nicely if you have properly cleaned it.