X-ray fluorescence of metal atoms in paint pigments is a non-destructive way to discover the material composition of paintings. Beginning with a prototype developed at Winterthur in the early 1970's, the technique has enjoyed large scale success in identifying forgeries and tracing pigment usage trends. Our purpose here was not so much to create a new X-ray fluorescence device (XRF) as it was to design an XRF to be used specifically in analysis of paintings; commercially available XRFs have generally been used in archeometric applications, examining metal or ceramic objects.