Continue the process from spot to spot or area by area. Thoroughly rinse the pottery in running water to remove excess acid. Remove iron oxide stains with 10 percent oxalic acid or 5 percent EDTA and rinse thoroughly. Remove iron sulfide and organic stains by immersing in 10-25 percent by volume hydrogen peroxide. This is especially important if the artifact will be reconstructed.
Many sedimentary rocks can absorb soluble salts and be stained.
The same treatments and chemicals described under pottery can be used, but the acids should be no stronger than 5 percent. The acids can be used effectively on metamorphic and igneous rock. The conservation of ceramics recovered from a marine site is not complicated. When pieces are found encrusted, the most difficult part of the conservation process is the removal of the adhering material without damaging the paste or glaze. For this reason, mechanical cleaning techniques are preferred, but hydrochloric acid is used with some regularity to remove calcareous encrustation.