In a preparatory step, the cross-section of the prepared specimens was first observed in an IR microscope. Pseudo-colour Gram-Schmidt plots of IR maps in reflectance mode were generated to provide a visual representation of the chemically modified/unmodified regions within the cross-section of the specimens. The Gram-Schmidt signal provides the integral IR reflectance intensity over all wavenumbers in the spectral range of the experiment. However, it must be considered that the surface quality will also interfere with the scattering intensities.