This reprint includes a short general article and a Kevex technical data sheet relating to the qualitative non-destructive analysis of paintings using x-ray fluorescence (XRF) with a radioisotope excitation source (in this case ⁵⁵Fe and ¹⁰⁹Cd). The technique is also called EDX (energy dispersive x-ray spectroscopy) or more properly, REXES (radioisotope-excited x-ray energy spectrometry). The method is used in authenticity studies to determine whether the elements present in a painting are consistent with those in pigments known to be available at a particular period or location, or used by a certain artist. Even the fingerprint analysis of a particular color tone may be characteristic of an artist. Spectra are illustrated from a painting of Queen Mariana of Austria attributed to Velasquez (1658) showing the presence of lead, strontium, iron and calcium; a portrait by Gauguin contained lead, zinc, barium, sulfur, iron and strontium. Dating or determination of location of origin may also be determined on museum artifacts in comparison with a computer databank of analyses of comparable materials.