The Laboratorie de Recherche des Musées de France in collaboration with the CEN Grenoble has performed a series of tests on samples of ancient polychromed woods in order to establish if the consolidation procedure impregnation in a vacuum -- polymerization with gamma rays would alter the polychromes. Stratigraphy of pictorial layers, the nature of pigments and binders, and the changes of color and aspect and the eventual morphologic modifications of layers after treatment were studied. The techniques used were those of optical microscopy (examination of perpendicular cuts) and physico-chemical analysis (x-ray microfluorescence coloration and heat tests on thin layers).