Infrared spectra of several different black inks on paper were obtained by FT-IR photothermal beam deflection spectroscopy (PBDS). Even though the manuscript samples contained about 0.1-0.5 μg of ink solid, spectra of sufficient quality were obtained to enable us to tell which inks contain carbon and to permit some differentiation between similar black inks to be made. However, the identification of an unknown ink is not feasible at present. Spectra of the ink printed on two stamps, and of the black print of a dollar bill, were also recorded. IR/PBDS studies of manuscript and print are totally nondestructive, and may prove to be useful in the fields of forensics and art history.
P. G. Varlashkin and M. J. D. Low, "FT-IR Photothermal Beam Deflection Spectroscopy of Black Inks on Paper," Appl. Spectrosc. 40, 507-513 (1986)