IMAGING FTIR SPECTROSCOPIC INVESTIGATIONS OF WOOD: PAINT INTERFACE OF AGED POLYCHROME ART OBJECTS

Most infrared spectroscopic investigations of painted artobjects so far focused on the study of pigments or bindingmedia. Only a few works involved studies of the woodencarrier. In this work the damaged medieval altar from theSt. Bartholomaeus Church in Recknitz, Northern Germany,was studied. The research focused on the IR spectroscopicinvestigation of its wood and ground layer.Cross sections of 10 μm thickness were made to enablestudies in transmission mode. The appropriate method formicrotoming was investigated. FTIR imaging with high spatialresolution was carried out using a FPA detector consistingof 64 x 64 single detectors. In combination with anIR microscope an area of (267 x 267) μm2 could be measuredat once.FTIR imaging turned out to be a useful technique to investigatethe wood-ground interface. The measured spectrawere evaluated using univariate (e.g. displaying the intensityof one band) and multivariate data analysis. The dataevaluation was supplemented by the multivariate methodscluster analysis and principal component analysis. Bothmethods showed clearly the separation of the main componentsof the part of the studied altar (wood, animal glue,chalk) as well as localized changes in the IR spectra of thewooden carrier.