Apply more of the sealer used on the porcelain to the tiles using a foam paintbrush. Sealer can frequently emulsify itself, softening the old sealer so it can be wiped away easily. Allow the new sealer to soften the old for approximately 10 minutes, and wipe up the sealer with a lint-free cloth.
Apply a sealant stripper to the tiles if the sealer has not emulsified. Apply the stripper to the stone with a foam paintbrush. Wipe the tiles with a lint-free cloth to remove the stripper and the sealant.
Rinse the tiles with water to remove any traces of the stripper or the sealant. Allow the tiles to dry naturally.