If your porcelain sink is lackluster no matter how hard you scrub you can renew it with a paste made from the juice of a whole lemon and 1 cup of borax. Using a scrub brush apply all over your sink. Let it sit for about 3 minutes. Rinse off. Viola! Your sink will shine because the mildly abrasive borax lifted the stains while the lemon acted like a bleach.