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UV-Vis fluorescence spectroscopy is a convenient non-invasive tool to study polychrome historical objects. It can help to identify the nature of certain materials when they present specific fluorescent properties. However, given the complexity of such stratified and heterogeneous materials, the attribution of the detected fluorescence to a specific constituent (e.g. a pigment or a binder composing a paint layer) is not straight forward. Moreover, the experimental data need to be corrected for a number of effects that can influence the recorded spectral distribution. The application of the self-absorption correction procedure (that require the simultaneous recording of reflectance profiles) [1,2] to experimental fluorescence data gathered on the polychromatic surface of the Codex Borbonicus, a 16th century Aztec manuscript, is described. The results are confronted to a different methodology [3] that is based on the hypothesis of transparent non-scattering paint layers. This second approach allows to establish more clearly the material origin of the detected emission and to discriminate apparent fluorescence (emitted by the substrate and transmitted through the paint layers) from intrinsic emission generated by the coloring materials under study. As a matter of fact, most of the various emission profiles measured in the paint layers of the studied manuscript actually originate from the substrate, and should not be used to characterize the coloring materials. This study demonstrates how carefully fluorescence spectroscopic and imaging data recorded on complex and stratified materials should be interpreted.
[1] C. Clementi, C. Miliani, G. Verri, S. Sotiropoulou, A. Romani, B.G. Brunetti, a Sgamellotti, Application of the Kubelka-Munk correction for self-absorption of fluorescence emission in carmine lake paint layers., Appl. Spectrosc. 63 (2009) 1323–30. doi:10.1366/000370209790109058.
[2] G. Verri, C. Clementi, D. Comelli, S. Cather, F. Piqué, Correction of ultraviolet-induced fluorescence spectra for the examination of polychromy., Appl. Spectrosc. 62 (2008) 1295–302. doi:10.1366/000370208786822296.
[3] F. Pottier, A. Michelin, C. Andraud, F. Goubard, B. Lavédrine, Characterizing the Intrinsic Fluorescence Properties of Historical Painting Materials: The Case Study of a Sixteenth-Century Mesoamerican Manuscript, Appl. Spectrosc. 72 (2018) 573–583. doi:10.1177/0003702817747276.
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