Using Paint to Investigate Fires: An ATR ‐ IR Study of the Degradation of Paint Samples Upon Heating

Fire investigation is a challenging area for the forensic investigator. The aim of this work was to use spectral changes to paint samples to estimate the temperatures to which a paint has been heated. Five paint samples (one clay paint, two car paints, one metallic paint, and one matt emulsion) have been fully characterized by a combination of attenuated total reflectance Fourier transform infrared (ATR‐IR), Raman, X‐ray fluorescence spectroscopy and powder X‐ray diffraction. The thermal decomposition of these paints has been investigated by means of ATR ‐ IR and thermal gravimetric analysis. Clear temperature markers are observed in the ATR ‐ IR spectra namely: loss of ν(C = O) band, >300°C; appearance of water bands on cooling, >500°C; alterations to ν(Si–O) bands due to dehydration of silicate clays, >700°C; diminution of ν( CO 3 ) and δ( CO 3 ) modes of Ca CO 3 , >950°C. We suggest the possible use of portable ATR ‐ IR for nondestructive, in situ analysis of paints.