Elemental identification of document paper by X-ray fluorescence spectrometry

The use of the elemental composition, determined by energy dispersive X-ray fluorescence (EDXRF), to identify different sorts of paper is reported. The concentrations of K, Ca, Ti, Mn, Fe, Cu, Zn, Rb, Sr and Ba were determined in sheets of an Italian book from 1941 with 200 pages. A dendrogram based on the elemental composition of each sheet, demonstrated three major groups of paper. Each group is formed by more than one paper block. This information allowed the box plotting for the three clusters which demonstrate the different elemental composition between the clusters and the identification of each of them. Cluster 1 could be identified by any of the concentrations of Ca, Cu, Zn and Ti, cluster 3 was identified by the concentration of Ba and Sr, while cluster 2 could be identified by considering all the elements together. These statistical results allowed us to conclude that this document was manufactured with three different kinds of paper. Applying Spearman coefficient correlations, strong positive correlations were found between K-Ca, Ti-Ca, Mn-Fe and Sr-Ba in the paper of cluster 1. For cluster 2 high positive correlation was observed between Ca-Fe and strong negative correlations were obtained between Ca-Sr and Fe-Sr. For the third cluster only a positive correlation was ;observed between Sr-Ba. Applying the Spearman coefficient correlations to the whole book, no correlations were observed. These results confirm the assumption that papers can be characterized using trace elemental concentration.