Microscopic examination of cross sections of the paint layers, taken from damaged areas of a picture, can help to establish how the painting was created. Putting together the original sequence used in adding the different layers of priming and paint can explain the process used by the artist. This can also be used to help identify which pigments were used. Key pieces of information can often be gleaned from the smallest areas.
Detail of a feather taken from a medieval manuscript
This image represents an area of the order of 5mm in width in the original