Our study of painting supports would not be complete if we did not also consider the possible influence of different wood varieties on the composition of the grounds used to prepare and protect them. Early authors were not shy when it came to detailing the preparatory techniques painters ought to use before starting work or on ways of protecting the backs of panels. Theophilus Presbyter (ca. 1070–1125), Cennino Cennini (ca. 1370–ca. 1440), Giorgio Vasari (1511–1571), and André Félibien (1619–1695) do not provide us with much information on the construction of the panels, but they are an important source when it comes to every detail of their preparation. Cloth soaked in size or ground (enduit), fibres and parchment were all used to cover the front and rear surfaces of a panel, to protect the wood, and to prepare it for the application of the paint layer.

We based our study on a reading of these historical texts and on direct examination of the works themselves, backed up by laboratory analysis. Rather than seeking to perform a systematic study, we carried out a number of tests on those paintings from each school that lent themselves best to this purpose. As we will see, however, the results we obtained are sufficient to offer a fairly accurate view of the nature and composition of the preparation, and we do not believe that a more systematic study could give rise to different conclusions.

The laboratory analyses were carried out on fifty-seven samples, broken down as follows:

•Grounds	22
•Cloth	22
•Plant fibre	10
•Animal fibre	1
•Parchment	2

Samples were taken from panels belonging to the French, Italian, Flemish, German and Spanish schools. The results we obtained are summarised in the overview at the end of Part 3, taking care to specify the nature of the wood used in the support for each panel.