The use of X-ray photoelectron spectroscopy (XPS) to assess the locus of failure of a photo-cured resin on an alumina substrate is reported. It is shown that the carbon Is spectra obtained with conventional (achromatic) and monochromatic photon sources are markedly different. The spectrum obtained with the monochromatic source reveals the fine structure associated with the polymer whilst the spectrum recorded with the conventional source is distorted by differential charging. This observation has important ramifications when XPS is used for the definition of the locus of failure of organic coatings, or adhesives, applied to insulating substrates such as ceramics.