Abstract: A crude conservation film was found that formed naturally on the surface of some historic stone buildings and monuments. It was so well preserved
that the stone inscriptions under the film were not damaged though they were made one more thousand years ago. In this contribution, the composition
and origin of the crude conservation film were focused. The samples of the film were analyzed by FTIR, PLM, EDAX, SEM and TEM. The results show that
the film consists mainly of calcium oxalate and there is a microbial involvement in the calcium oxalate film. There is no clear dividing line between the carbonatematrix and oxalates film. The
transformation layer is about 15μm thick. The thin bioinorganic film is very compact non-porous shell and the calcium oxalate is far more acid
resistant than that of calcium carbonate. The forming mechanism was discussed and the chemical bionics of this crude film was also researched.

Key words: cultural relic, conservation, calcium oxalate, bioinorganic film