Pyrit i arkeologiska benföremål – ett dolt problem? Undersökning och skadeinventering av järn och svavel i arkeologiska ben- och benhornföremål

Abstract

The number of publications concerning problems with pyrit (FeS2) and pyrite oxidation in archaeological objects made of bone or antler is limited. Problems with oxidation of unstable pyrite are well known in mineral collections, marine archaeological wood as well as archaeological skeletal remains. High levels of relative humidity seem to promote oxidation. Is there an overlooked problem regarding archaeological objects made out of bone or antler? An inventory in four Swedish museum stores did not reveal any significant problems with cracking, flaking, or delamination of bone and antler objects. About half of the damaged objects displayed a discolouration of the surface of the cracks, indicating a possible iron/sulphur source of the problem. Small fragments from damaged objects as well as samples from two marine archaeological bovine skeletal remains from the warship Kronan were analysed with SEM-EDX (scanning electron microscopy – energy-dispersive X-ray spectroscopy). Both sulphur and iron were detected in two composite object. In objects without any discolouration of the damaged surface, only the phosphorous and calcium from the inorganic component of the bone material were detected. The bovine skeletal remains from the warship Kronan showed sulphur and iron in various proportion in the surface layer. As there seems not to be any general problems within museum stores storage due to pyrite, there is no reason to modify the general climate recommendations for archaeological bone- and antler objects. However, as a few objects showed damage probably due to iron/sulphur problems, a review of conservation procedures for specific objects is recommended.