Varnish is rare on the great majority of the paintings by Norwegian artist Edvard Munch (1863–1944). Empirical experience has shown that many of his oil colors are notably vulnerable to dirt removal, especially the lean blues, greens, yellows, reds, and whites. The removal of firmly attached dirt and dust (or any other impurities, e.g., tide lines from water stains or bird droppings) is and will continue to be utterly challenging for Munch’s unvarnished paintings. This is particularly evident in paintings that are not protected by airtight, glassed frames, as is the case of Chemistry, one of the artist’s 11 large-scale canvas paintings for the Aula of Oslo University (1914–1916). For over 30 years, the surface of Chemistry (about 444 × 220 cm2) had been exposed to vast amounts of airborne pollutants, severely soiling it. In 2008, various aqueous and mechanical cleaning tests were performed. In order to evaluate the efficacy and harmfulness of each cleaning method with respect to the different colored areas of the painting, a noninvasive methodology based on in situ spectroscopic measurements, as well as visual examination, was carried out.