Identification of iron-gall inks in historical drawings by Fibre Optics Reflection Spectroscopy - Extension to the NIR spectral range

Previously developed chemometric tool for identification of corrosive iron-gall inks in historical drawings based on the target factor analysis of visible-near infrared fibre optics reflection spectra (Vis-NIR FORS) in the range of 500-1050 nm was extended to the NIR range of 1200-2300 nm. The extended method was found to be capable to distinguish sepia and bistre inks from iron-gall inks. Particularly the resolution of bistre inks is more reliable comparing to the previous method. Examples are taken from the analysis of the 16th through 19th centuries historical drawings from the collection of Slovak National Gallery in Bratislava. The results of analysis based on this tool were confirmed by XRF spot analysis.