Mössbauer Study of Iron Gall Inks on Historical Documents

Abstract Iron gall ink was used as a permanent writing material already in late Roman times and throughout the Middle Ages, until it became obsolete in the 20th century. There is much interest in non-destructive experimental methods to determine the state of the ink and its degradation products on historical documents. Mössbauer spectroscopy is such a method, and it has the particular advantage to be sensitive to the chemical bonding of iron, but this method has only rarely been applied to historical documents. In this paper we present Mössbauer data for two damaged documents from a Library in Granada and a handwritten German book from the 18th century. These new results are discussed in the context of previously published Mössbauer data. In one of the investigated documents Fe-(II)-oxalate, FeC2O4·2H2O, was observed. The assignment of the various Fe3+ sites in the different documents is rather difficult and often there is a superposition of various species. These species can be remains of the Fe-tannin complexes of the ink, complexes of Fe3+ with the cellulose of the paper and different iron oxide or hydroxide nanoparticles.