For General Cleaning, use weak to moderate concentration acids (except hydrofluoric) or alkalis. Also acceptable are detergents, abrasives, and standard soap. Burning off organic residue by gas burner or furnace is also acceptable.
For porous ceramic, use weak to moderate concentration acids (except hydrofluoric) or alkalis. Back flushing is also a method commonly used to unclog pores. For surface deposits, light sanding may be acceptable.