Layers of calcium-sulfate-based preparations on some 14th-, 15th-, and 16th-century Italian paintings on wood were studied. The presence of one single coating or else two different coatings was evidenced by various observation techniques: specific coloring, polarized microscopy, and scanning electron microscopy (SEM). X-ray diffraction analysis (XRD) completed these results. Backscattering electron imaging was used to try to elucidate the natural or artificial origin of the gypsum and anhydrite.