The Painting index has been set out according to (a) the type of wood, (b) the school, (c) different regions or towns where paintings are located and (d) attribution. Within this framework, paintings are placed in chronological order. However, masters and their schools have not been separated and the alphabetical order of artists has been followed wherever possible, even if it slightly alters the strict chronological order.

The panels were studied systematically, each panel of an ensemble being considered as an individual panel and therefore subjected to the same examinations (for wood type and method of construction) as a single panel painting. Thus an altarpiece has been allocated numbers that accord with the number of panels of which it is composed. Dimensions are recorded as (1) height, (2) length and (3) thickness. The measurements given are always the maximum dimension.

Generally, the numbers in brackets after the name of the museum designate the number of the painting in the museum catalogue and/or the inventory number. For the Musée du Louvre, they refer to Brière 1924 for the French School, Demonts 1922 for the Flemish, Dutch and German Schools and Hautecoeur 1926a for the Italian and Spanish Schools. Since the numbers of the paintings in these catalogues are not listed in chronological order, the corresponding page number is cited. Index numbers in square brackets indicate paintings that are not included in the statistics in the main text due to uncertainties regarding their attribution but do provide useful information.

The sample number corresponds to the microscopic analysis of the wood of the panel and precedes information that applies exclusively to the reverse of the painting so that all indications of orientation (right and left) are as seen from behind. By contrast, where left and right ‘wings’ are indicated, this is from the spectator’s point of view (i.e. from the front). Only the indisputable results of the wood analysis have been recorded. However, identification of oak and certain poplars is simpler therefore these were not always examined in the laboratory but by a skilled biologist and are indicated in the text by ‘Visual examination’ rather than Sample’.

Observations of the construction of the panels are often incomplete – the positioning of paintings on exhibition and the regulations that had to be observed did not always permit full examination. However, whenever possible the direction of the grain of the wood, the number of boards and the way in which they were assembled are noted. The physiognomy of the reverse of each painting is described as accurately as possible as well as the different elements in their construction or protection, whether original or later. An attempt has been made to trace the history of the reverse of each panel since its construction, giving a lesser (but not negligible) value to more recent additions. Any information on the state of the wood is provided simply for documentation purposes and is not an indication of either the state of conservation or the strength of the wood. This study is not a conservation survey.