Our study of the wood used to construct painting supports from the 11th to the 16th century led us first to examine the different methods employed to assemble the panels. We then explored the various ways in which the fronts and backs of the supports were prepared. Our goal in all this was to ascertain the extent to which the choice of wood influenced construction and preparation and vice versa. The resultant observations enable us to derive a number of general rules, together with customs specific to certain schools or eras. These conclusions may be of interest to art historians and will, we hope, contribute to the identification of certain works.

Port cities displayed a degree of bustle and activity which, compared to the relative immobility of other regions, must have seemed highly intense to contemporaries. The timber unloaded from Meuse barges at French quaysides, from Dieppe to Bordeaux, was essentially used for shipbuilding. Only rarely was the expense incurred of carting wood – which could be procured from local forests – to the hinterland. Imported timber was thus consumed by the large-scale industrial activity of the shipyards. The day-to-day needs of carpenters, joiners, cabinetmakers, cartwrights and other craftsmen could be readily satisfied by local materials.1Editors’ note: One rare case of the use of local oak wood (Guislain- Wittermann 1996). Many studies since the 1960s have established a picture that is far more nuanced than was possible by the study undertaken by Marette and her team. The influence of international trade on painters’ practices, particularly where imported Baltic oak was concerned, offers perhaps the most significant revision to her arguments. See Chapter 5 for references.

Systematic laboratory analysis of wood samples taken from just under twelve hundred paintings from different European schools confirms that regional wood was used to construct painting supports. The results of this research form an extremely close match with known forestry patterns in the period in question, adding rigour to the rule that can be extracted from them. Striking confirmation is provided, moreover, by the fact that Leonardo da Vinci (1452–1519), who painted on poplar in Italy, used walnut when working in France, just as 16th-century French painters did; and that the Flemish painter Justus of Ghent (ca. 1410–ca. 1480) used poplar while he was working in Urbino on the series of portraits for Duke Federigo di Montefeltro rather than the oak that was customary in Flanders.

If we accept this rule, we have to view a painter’s use of a wood that was foreign to his region as an anomaly, and in particular the employment of walnut by the northern schools, fir by the English School,2Editors’ note: When the author makes this point in Chapter 4 (almost verbatim), she says ‘the English and Flemish schools’. spruce by the Spanish and peninsular Italian schools, thuja anywhere other than the southern Iberian Peninsula, beech in central and southern Spain, and maritime pine in Aragon and Catalonia. We also found a certain number of wood species, the use of which we do not consider to be anomalous but simply unusual. The wood in this case was either rarely employed or rarely found in the region in which it was used, but is still normal.

Examination of the statistics reveals the dominant species for each school, together with others which, while secondary, remain characteristic of the school in question inasmuch as they are only employed in that region, even though they exist in several others. Oak is dominant, for instance, in Flanders and in northern France, poplar in Italy and softwoods in Germany. Walnut, chestnut and lime, meanwhile, are characteristic of southern France, the Viseu School and certain German schools, but are by no means dominant there.

Out of the twelve hundred paintings we studied, we only found the following eight anomalies:

Various hypothetical explanations may be advanced to explain the origin of these anomalies, beginning with the circumstances in which the work was created and its intended purpose. A panel from a piece of furniture made by some renowned craftsman in his own country, for instance, might subsequently have been sold or rented to a wealthy foreign customer, who took it abroad. The panel could then have been painted by a local artist, resulting in a painting from a specific school done on a foreign panel. This hypothesis would explain the panel with the Scenes from the Life of the Virgin from the Northern Netherlandish School. The anomaly is explained if this is a panel from a chest made in France and painted in the Netherlands.

We should also take account of proximity to a port and to the status and wealth of the person or body who commissioned the work, who might have been engaged in importing expensive foreign goods. The artist could then have painted on boards used for packaging or imported for furniture-making. Careful study of a particular anomaly will occasionally enable us to review or fine-tune an attribution. The fact that artists in this period exclusively used wood of local origin should not be interpreted as indifference on their part to the choice of material. On the contrary, as we found for the French and Spanish schools in particular, contracts between artists and their patrons were very specific when it came to the type of wood to be used and how it was to be prepared.

Study of how the supports were constructed offers some equally interesting, albeit much more limited lessons. Respect for the work of art means that it is not always possible to examine it in detail. What is more, this kind of study becomes much more complicated when alterations have been made over the years to the back of the panel. It would appear, however, that construction techniques depended more on the particular school and period than on the nature of the wood.

Cutting tools varied very little in Europe until saws came into common use in the 17th century. Construction methods, by contrast, evolved more significantly over time. Assembly in the 12th and 13th centuries with butt joins, primitively executed and glued or filled, later progressively gave way to the use of dowels. Lastly, more complex systems employing tongue and groove or spline joints appeared in every school in the course of the 15th and 16th centuries.

Simple cross-bars, fixed to the surface of the panel by nails driven through the front, are found most frequently in the Mediterranean countries. They are much rarer in central Europe, where nails were often replaced with wooden dowels. The use of highly specific, cross-shaped reinforcement systems is likewise characteristic of the Spanish schools. Simple surface-mounted cross-bars were later replaced by recessed bars, mostly dovetailed.

Analysis of the grounds shows them to be the same for all the medieval schools,11Editors’ note: The discussion in Chapter 11 is supplemented with references that revise this conclusion. but their composition and thickness could vary from one period and one school to another. Use of cloth, fibres and even parchment, soaked in thick size or ground (enduit), are particularly characteristic, for instance, of the Spanish and German schools. Similarly, panels painted on both sides and held in rebated frames are more common in the Germanic countries, in France, and in Flanders.

As one would expect, knowledge of the chemical properties of wood was very limited at the time; on the other hand, its physical and mechanical characteristics were understood very well. Craftsmen recognised the value of quarter-cut wood, and knew that by juxtaposing different cuts they could limit warping of the panel. Different types of wood were consciously used to construct the secondary elements of the support, such as the dowels, the reinforcements, the frames and the carved elements.

Knowledge of woodworking was so advanced in the Middle Ages that we might well call it a science, albeit an empirical one. It was not until much later, in 1764, that Duhamel du Monceau (1700–1782) published a treatise that would set out the first scientific principles for the study of wood. We do not wish to get ahead of ourselves, however, and so our study concludes at the end of the 16th century. The validity of these conclusions cannot therefore be extended beyond this period. A new era was about to dawn in economics and international trade relations. The appearance of exotic wood types would provide the Old World with new raw materials. Trading in wood, which had previously been limited, now developed and the price of imported timber began to fall.

We hope that others will extend our study beyond the limits we have set ourselves. Their findings will no doubt be very different. This is hardly surprising, since artists are subject to the customs of their time. When transport was rare and expensive, and when artists were viewed simply as skilled craftsmen, painters were naturally obliged to work on local materials. We should undoubtedly be grateful for this fact since, given our knowledge of local forestry resources at the time, we can exploit it as a new element in the study and identification of paintings.