painting is a multi-layered work of art, where knowledge regarding one of those layers can reveal a great deal about the painting as a whole. Cross-section analysis allows detailed investigation of the ground layer, imprimatura layer, underdrawing, paint layer and varnish layers which can provide important information on the chosen materials and the technique of the artist, as well as materials used in previous restorations. The analysis of small details can therefore lead to successful attributions and appraisals of a work of art and help determine its geographical origin. For instance, discovering chalk, charcoal and lead white pigment in the imprimatura mix of one of many versions of the Bird Trap by P.Brueghel II (as well as analysis of the underdrawing, ground and paint layers) led experts to conclude that the work in question was in fact painted by the artist himself, as opposed to a student or contemporary copyist.
Cross-sections are made by embedding tiny samples in polyester- or acrylic resins, which are then polished repeatedly to get a higher degree of detail. The use of SEM-EDX (scanning electron microscope) yields high resolution images of the surface topography, which are produced using a highly-focused, scanning electron beam. The smallest detail that can be seen on a SEM image is 4-5 nanometer (millionth of a millimeter).
SEM-EDX analyses of cross-sections is done at an external location.