Evaluation of the effect of six different paint cross section preparation methods on the performances of Fourier Transformed Infrared microscopy in attenuated total reflection mode

The purpose of the present research was to compare the effect of different embedding and polishing procedures on the performances achievable with Fourier Transformed Infrared (FTIR) microscopy in Attenuated Total Reflection (ATR) mode. The attention was specifically focused on this technique since it is generally considered one of the most appropriate methods to analyze cross sections, thanks to the fact that the recorded spectra are similar to those collected in transmission mode. The research work was structured as a round robin among six different conservation and research laboratories. They were asked to embed fragments derived from the same area of a real sample following each one a different procedure. The performances of FTIR microscopy in ATR mode were evaluated on the different cross sections, considering the cross section morphology and the possible source of contamination. The cross sections were previously observed with optical microscopy, Environmental Scanning Electron Microscope (ESEM) and confocal microscopy. Three procedures were eventually selected, because they provided the best results in terms of both limiting the contamination of the embedding medium and achieving good contact with the ATR crystal. They were: a) embedding in KBr; b) cyclododecane pre-treatment before embedding in an organic resin and cutting of the sample; c) embedding in an organic resin and polishing with argon ion milling. These three procedures were finally compared and the weak points outlined, indicating where improvements could be made for further researches.