Application of attenuated total reflectance—Fourier transform infrared spectroscopy—(ATR-FTIR) and principal component analysis (PCA) in identification of copying pencils on different paper substrates

Abstract Presence of copying pencils in heritage objects poses a significant challenge for conservators due to their proneness to fading, sensitivity to solvents and difficulties in differentiation from regular graphite pencils. In this paper a method of copying pencils identification by means of ATR—FTIR spectroscopy is used. A protocol for spectra processing and dimensionality reduction of spectral data by means of principal component analysis has been developed, allowing for pencil types differentiation and providing an easy to read visual representation of the collected data. The protocol has been developed on mock-up samples and tested on objects from the archives of the State Museum Auschwitz – Birkenau.