panel painting

A panel painting is a painting made on a flat panel made of wood, either a single piece, or a number of pieces joined together. Until canvas became the more popular support medium in the 16th century, it was the normal form of support for a painting not on a wall (fresco) or vellum, which was used for miniatures in illuminated manuscripts and paintings for the framing.

Panel construction and preparation

The technique is known to us through Cennino Cennini's The Craftsman's Handbook (Il libro dell' arte) published in 1390, and other sources. It changed little over the centuries. It was a laborious and painstaking process:

1.     A carpenter would construct a solid wood piece the size of the panel needed. Usually a radial cut piece was preferred (across rather than along the length of the tree; the opposite of most timber cuts), with the outer sapwood excluded. In Italy it was usually seasoned poplar, willow or linden. It would be planed and sanded and if needed, joined with other pieces to obtain the desired size and shape.

2.     The wood would be coated with a mixture of animal-skin glues and resin and covered with linen (the mixture and linen combination was known as a "size"); this might be done by a specialist, or in the artist’s studio.

3.     Once the size had dried, layer upon layer of gesso would be applied, each layer sanded down before the next applied, sometimes as many as 15 layers, before a smooth hard surface emerged, not unlike ivory. This stage was not necessarily done after the 16th century, or darker grounds were used.

Painting Techniques

Once the panel construction was complete, the design was laid out, usually in charcoal.

The usual ancient painting technique was encaustic, used at Al-Fayum and in the earliest surviving Byzantine icons, which are at the Saint Catherine's Monastery, Mount Sinai. This uses heated wax as the medium for the pigments.

This was replaced before the end of first millennium by tempera, which uses an egg-yolk medium. Using small brushes dipped in a mixture of pigment and egg-yolk, the paint was applied in very small, almost transparent, brushstrokes. Thin layers of paint would be used to create volumetric forms.

By the beginning of the 15th century, oil painting was developed. This was more tolerant, and allowed the exceptional detail of Early Netherlandish art. This used a very painstaking multi-layered technique, where the painting, or a particular part of it, had to be left for a couple of days for one layer to dry before the next was applied.

Conservation and scientific analysis

Wood panels especially if kept with too little humidity, often warp and crack with age, and from the 19th century, when reliable techniques were developed, many have been transferred to canvas or modern board supports.

Wood panel is now rather more useful to art historians than canvas, and in recent decades there has been great progress in extracting this information - and many fakes discovered and mistaken datings corrected. Specialists can identify the tree species used, which varied according to the area where the painting was made. Carbon-dating techniques can give an approximate date-range (typically to about a range of about 20 years), and dendrochronologysequences have been developed for the main source areas of timber for panels. Italian paintings used local or sometimes Dalmatian wood, most often poplar, but including chestnut, walnut, oak and other woods. The Netherlands ran short of local timber early in the 15th century, and most Early Netherlandish masterpieces are Baltic oak, often Polish, cut north of Warsaw and shipped down the Vistula, across the Baltic to the Netherlands. Southern German painters often used pine, and mahogany imported into Europe was used by later painters, including examples by Rembrandt and Goya.

In theory, dendro-chronology gives an exact felling date, but in practice allowances have to be made for a seasoning period of several years, and a small panel may be from the centre of the tree, with no way of knowing how many rings outside the panel there were. So dendro-chronological conclusions tend to be expressed as a "terminus post quem" or an earliest possible date, with a tentative estimate of an actual date, that may be twenty or more years later.

The so-called Panel Paintings Initiative is a multi-year project in collaboration between the Getty Conservation Institute, the Getty Foundation, and the J. Paul Getty Museum. The Panel Paintings Initiative is a response to the growing recognition that significant collections of paintings on wood panels may be at risk in coming decades due to the waning numbers of conservators and craftspeople with the highly specialized skills required for the conservation of these complex works of art.