The study of the artworks of the Old Masters has long been the prerogative of art historians alone. Expertise and other art-historical methods can now make much greater use than ever before of the findings of the so-called exact sciences. These make it possible to acquire new knowledge about works of art of the past that is not obvious to our eyes. Imaging and instrumental methods for the study of works of art often allow us to literally “look into the painting”, below the surface of what we see, and observe the work in different areas of the invisible spectrum of electromagnetic radiation, for example. By using various research methods – with the necessary caution and awareness of their limitations – it is often possible to gain insight into the hypothetical process of the creation of the work and into the painting’s layers. It is possible to characterize the material nature or technological processes or to study the author’s changes and later interventions in the work. Various research methods allow us to see artworks from different perspectives and to study them figuratively speaking “in new colours”, often the colours in which they appear to our eyes using a variety of imaging methods. How an art historian can work with technological knowledge and to what extent he can rely on it at all is demonstrated and addressed in a total of seven case studies dealing with hanging paintings by Old Masters from the collections of the Archbishopric of Olomouc and the Olomouc Museum of Art.