Identification tags for archival documents based on oxides of transition and inner transition metals – influence on paper supports

Abstract Theft of archival documents constitutes a serious problem for archives. A possible solution to this problem lies in labelling these documents with codes that are invisible to the naked eye. A possible method could involve use, e.g. of the oxides of lanthanum, dysprosium, samarium, gadolinium and niobium, which have good responses in the XRF spectrum and are normally not present in archival materials. This study is concerned with the impact of these oxides on the properties of lignocellulosic materials. The identification tags were printed on three different kinds of paper supports (Whatman No. 1 filter paper, paper according to ISO 9706 and sulphite pulp). The colour change, average degree of polymerisation, the pH values of an aqueous extract and selected mechanical properties after application of the tag and artificial ageing were studied on all the samples. The measurements showed that the studied oxides do not have a negative effect on the monitored properties of the paper supports and do not affect their long-term ageing behaviour.