Describes analyses that were performed on three canvas paintings by Correggio, the <i>Danae</i>, the <i>Compianto sul Cristo Morto</i>, and the <i>Martirio di Quattro Santi</i>, with special regard to the gray colors. Nondestructive x-ray fluorescence (XRF) measurements showed that the elemental composition of these colors included observable amounts of antimony, and that its abundance was related to the darkness of the color. Optical microscopy, scanning electron microscopy (SEM) and electron probe x-ray microanalysis (EPMA) analyses, carried out on a single sample taken from the <i>Danae</i>, confirmed that antimony was associated with the gray layers of the stratigraphical section and allowed the authors to hypothesize the presence of stibnite, which is a lead-gray colored antimony trisulfide.