The problems of old master paintings are different from modern art. Among the “old masters” we rarely find modern forgeries, the authentic materials being difficult to find and the pictorial technique being more complex. It is rather a question of confirming the attribution and determining the exact status of the work. Pre-modern artistic painting was organized and taught as a craft. Young artists generally trained as apprentices in a workshop directed by an established master. Many copies of well-known paintings exist, created by advanced apprentices as part of their training. These copies often represent high-quality works of art in their own right.
Workshops were run as commercial businesses. If a composition sold well, the master together with his employees and apprentices would often create multiple copies and versions, many of which still exist today. The aim of an investigation today is to distinguish between the different types of paintings which likely have very different value according to their status. Which one was the earliest work in a series of almost identical versions? How can one distinguish the original from an almost contemporary copy made by a pupil?
Technological studies also make works of art more interesting. A presentation for an intended sale gains a lot from the documentation of an elaborate underdrawing or from an X-radiograph matching others by the same artist.
Technological studies often present additional information inaccessible to the eye of the expert art historian. Infrared reflectography shows underdrawings, radiography highlights the pictorial technique not visible to the eye, and analyses allow the comparison of the palette with the pigments available and usually used by the artist in question.
In addition, throughout the centuries old master paintings have almost inevitably been subjected to multiple restoration interventions, sometimes very invasive. Before buying a work of art it is important to find out which parts of it have been restored, using ultraviolet light or X-rays, among other methods, to make informed decisions and avoid unpleasant surprises.