Frames and supports in 15th and 16th-century Southern Netherlandish painting

CHAPTER II 44 B. Joining the elements of a panel Exactly how the joining process was done is a matter of conjecture. We have no archive or iconographic sources from the time that can enlighten us. From our knowledge of the glues and tools available from the time, from later written sources, in particular the 18th century French writer Roubo, and from modern-day woodworking practice, we can venture the following. A key element here is that, in the Southern Netherlands, hide glues were used exclusively. Hide glues have to be applied hot. As the glue cools, it arrives fairly quickly at gel point, after which the resulting bond is significantly compromised. The joiner glued one board at a time. Two solutions have been suggested. A first solution is put forward by George Bisacca, from the Paintings Conservation Department of the Metropolitan Museum of Art in New York. George Bisacca points out that the key concern in assembling the panels was to get them lying absolutely flat on the painting side. The most effective way of doing this was to place the panels with the smooth (to-be-painted) side downwards on two or more absolutely straight and flat beams, then to place a second set of beams above these. The upper and lower beams were then clamped tight at the ends. At this stage the thicker ends of the boards are more or less flush with the upper beam, in each case leaving an elongated V-shaped gap between the upper beam and the board. Wedges are then driven into this gap, forcing the smooth side of the board absolutely flat against the lower beams. Working this way, each board was dry fit to the adjacent one. Any slight imprecision that occurred during the drilling and placement of the dowels could then be corrected by a relatively small planing adjustment across the join or an adjustment of the dowel itself. After completing each join, the entire ensemble could be assembled dry and the overall flatness checked and adjusted. At this point it would be ready for disassembly, application of the glue, reassembly, and clamping. The wedge shape of the board is of key importance here, not just an accident of process. Indeed, when the board is sawn on both sides, it is intentionally sawn pie-shaped, rather than having two parallel flat surfaces. Jean-Albert Glatigny, a panel restorer working in Belgium for the Royal Institute for Cultural Heritage, describes the process as follows: “The joiner places the first board horizontally on a sort of easel. After inserting the dowels, the joints are covered with hot hide glue, and the joiner places a second board, almost vertically, on the first. Drying is rapid (a few minutes). The dowel holes are rarely perfectly aligned from one board to another. The dowels are often slightly thicker in the centre so as to remain blocked to maintain the boards in place during the gluing process. The process is repeated until a complete panel is built. Only at this stage is the panel traced and cut to size, and the surface flattened and smoothed for painting, using first a scrub plane (with a slightly convex blade, and used diagonally to the grain) and then finer planes. On larger panels, temporary grooved battens could be nailed on the two sides across the grain to keep the panel flat and together during handling.”