H O P-M T C I 119thickness (35–40 mm), possibly required by their size and their simpler
structure, which entrusts the panel’s strength and stability to the board’s
rigidity. The boards of later paintings from the sixteenth and seventeenth
centuries are even thicker (40–45 mm) and are practically self-supporting—
with crossbeams and slats that are usually intended to guarantee the con-
tinuity of the panel rather than its overall strength or shape.
In most cases thickness is constant throughout the whole panel;
however, some panels were intentionally manufactured with varying thick-
nesses.^18 No satisfactory technical explanation has yet been given for this
feature, which has been seldom reported in panels from central Italy.^19Connections between boards
Boards were usually glued along their edges with “cheese glue” (casein)
or hot-melt animal glue (made of clippings), both described by Cennino
(Cennini 1994:chap. 108). Typically, boards were accurately square-edged
before gluing, and occasionally several incisions were made on the edges,
possibly to improve glue adhesion (Fig. 9).^20
Casein glue, one of the strongest glues known, has been used by
woodworkers since ancient times; it does not have tack,^21 and its pot life is
relatively short. Hot-melt animal glue features an even shorter preassembly
time, since it must be hot while pieces to be joined are pressed together.
For both glues, therefore, the assembly of boards had to be performed in a
relatively short time, and the process required accurate and definitive posi-
tioning before pressure was applied. To satisfy such requirements (which
must have been demanding, especially for large supports), wood splines, or
dowels, made of hardwood (such as oak or elm) were used (Fig. 10). The
splines were circular (cavicchi) or r ectangular (ranghette) in cross section.
They fit into mortises bored in the board’s thickness and were placed at
appropriate distances along the edges in order to maintain the board posi-
tion until the glue applied on the edges had set.^22
Other methods for connecting boards, such as groove-and-tongue
joints, were possibly also used in earlier times. However, such methods
seem to make gluing more difficult, because the internal surfaces were hard
to reach and to control. Half-lap joints were used only in special cases.
Although double-dovetailed (i.e., X-shaped) wooden cleats mor-
tised in the boards (Fig. 11) are infrequently found in the original manu-
facture of central Italian supports, their use has been popular in later
restorations, albeit with unsatisfactory results.^23
As an interesting example, the three higher corners of the cuspi-
date front frame of the Maestàby Duccio featured X-shaped cleats mortised
into the boards and then painted by the artist. The subsequent woodFigure 9
Incisions on the edges of the board to
improve gluing, and spline used for the align-
ment ofboards during the setting of the glue.
Francesco Salviati, The Deposition from the
Cross.