Portable spectrographic techniques have desirable attributes for archaeological investigations because they can be applied in the field non-invasively and non-destructively. With the increasing ubiquity of portable spectrographic techniques in Australia it is timely that the complexities of field-based analyses are discussed. A review of portable x-ray fluorescence (PXRF), including the limitations of the technique, and discussion of the complex physical interactions encapsulated by the resulting elemental data, provide a firm basis for interpreting the analysis of a rock art panel on the Woronora Plateau, New South Wales. PXRF data supports the results of previous (laboratory-based) pigment characterisations, that a locally sourced, composite clay-based paint was used to produce rock art. Results highlight the requirement for specific knowledge and expertise, not only in relation to the technique, but also the rock art under investigation and, critically, its taphonomic context. Ultimately this case study demonstrates that portable spectrometry should be considered an addition to the existing repertoire of archaeometric techniques applicable to the study of rock art, rather than as a replacement for laboratory analyses.