Nondestructive Multi-Elemental Analyses of Current-Size United States Federal Reserve Notes by Energy Dispersive X-Ray Fluorescence

Abstract

Energy dispersive X-ray fluorescence (EDXRF) was used to nondestructively determine the elemental composition of current-size $10 United States Federal Reserve Notes (FRN) from series 1928 to series 2003. The X-ray spectra from all the bank notes were cataloged into a digital spectral library for searching and comparisons of questioned bank notes. Paper and different color printing inks were analyzed to determine elemental composition. One of the components of the green ink on the back of the early issues was identified as being the compound pigment Pigment Green 15, also known as chrome green (PbSO4·xPbCrO4·yFe4[Fe(CN)6]) precipitated onto a base of baryte (BaSO4) and Paris white (CaCO3). Our data show that the concentrations of Pb in the green ink have declined since the first issue of Series 1928 and ended with Series 1988. EDXRF is an excellent analytical method for rapid nondestructive elemental analysis of bank notes. This elemental characterization is useful for authenticating bank notes for the numismatist and for the forensic scientist. The method described can also be used for quality control in the manufacture of bank notes and for evaluating how circulating bank notes deteriorate.