To establish standard working practices and further understanding of the application of X-ray fluorescence (XRF) spectroscopy to works of art and cultural heritage materials, a series of round-robin tests have been conducted biannually since 2002. In 2008 the round-robin explored the application of XRF to the study of paintings on canvas. Thirteen samples, consisting of both modern and traditional pigments on canvas, were distributed to 25 participating institutions for analysis. The samples were designed to explore common challenges encountered in the XRF analysis of painted works including peak overlaps, sum peaks, layering/shielding effects, detection of low-Z pigments, and modern pigments. The results from representative samples highlighting each topic are discussed.