Help with cleaning ceramic parts

WE have some ceramic parts that have been "scorched", as in they have been subjected to a lot of heat, and have become discolored, its almost as if the burnt look has been absorbed into the ceramic pores. We have tried numerous ways of cleaning them, with limited, or no success. Anyone have any suggestions? I would prefer a chemical method, if possible, as we don't want to harm the finish on these parts.

Porosity and cleaning go together like oil and water. The best way to clean this part without too much material removal is to use ultrasonic cleaning equipment and a chemical with a super good wetting agent There is a product with a 10.5 pH that has a dod2000 spec from Glenchem near Phila.,Pa.