An important distinction in the technical analysis of artworks is that between invasive and noninvasive methods. When possible, technical analyses are restricted to noninvasive methods that do not require removing any material from the object. Examples of noninvasive techniques include UV fluorescence, infrared reflectography, and reflectance transformation imaging. However, when it is not possible to answer critical questions with noninvasive methods, it can sometimes be warranted to remove minute samples from an artwork, for example, to identify a specific material. Invasive methods of analysis, usually referred to today as micro-destructive, include X-ray diffraction and infrared spectroscopy as examples. Paint cross sections can also be taken, such as when art conservators require more information about the precise layered structure of a painting in preparation for treatment. Before any micro-destructive investigation is carried out, researchers should carefully consider the location and the specific rationale for each of their samples and discuss these issues with museum curators. As long as the appropriate background research is in place, the wealth of information gained from these invasive but micro-destructive methods is considered to be worth the small amount of damage.
Ashok Roy, Director of Collections at the National Gallery, London, stated during his 1998 Forbes Prize Lecture that the cross section taken from Titian’s Bacchus and Ariadne at the Gallery was approximately a mere 0.000 0002% of the picture’s surface area. In his opinion, cross sections were an excellent way to study paintings that are often “complex multilayered structures…with enormously complicated chemistries.” The results from taking a cross section are actually more illuminating than those from many of the nondestructive methods available to the cultural heritage field. Each technique has its benefits and drawbacks. Often a number of techniques must be undertaken in order to provide the “ puzzle pieces” needed to see the overall picture. Whatever the technique, the safety of any artwork is paramount.