Straub prefers an adhesive type that is water- and mold-resistant. He
emphasizes casein glue over animal glues and discusses all new synthetic
glue types, among them epoxy resins, following the outlines of Anthony
Werner (Straub 1963:141, 145, 171).
To support the bend of a warped panel during the gluing
process, auxiliary constructions should be made. Sometimes butt joints
are damaged by insects, reducing the quality of adhesion. Cuts can be
made, and a small slat of the same dimensions can be inserted and glued
(Wolters 1952:14–15). Brachert also describes this early technique, noting
the use of the Keillade, an old joiner’s tool (Brachert 1955b:19, 21).
Wehlte also refers to this tool and illustrates its advantages in a case study
(Wehlte 1965:37–41).
This apparatus proves helpful for rejoining smaller panel paint-
ings. Broken panels can be warped nearly spherically, making it necessary
to hold the parts of the panel in complicated positions to get the joints
into perfect three-dimensional contact. Straub presented a modified appa-
ratus for rejoining thick, heavy Catalan panel paintings, the basic mecha-
nism of which had been developed by Hermesdorf (Straub 1956:192–94;
Hermesdorf 1953:87–91). Some years later Straub presented a construction
in steel and iron that was very similar to his first construction of wood
(Straub 1961:44). In the international conservation scene in the 1960s,
more technical constructions were described that permitted better rejoin-
ing ofpanels. Niedermann presented another simple apparatus
(Niedermann 1979:51–54).Early and modern auxiliary methods to reinforce glued joints
An examination of the original backs of medieval and later panel paintings
reveals the numerous methods that have been used to reinforce the joints
of a panel (Straub 1984:139–42). Oakum, calf hair, or horsehair was glued
along the butt joint. In other cases, canvas strips cover the joints (Zehnder
1990:471, Wallraf-Richartz-Museum, Cologne, inv. 128). Sometimes
butterfly inser ts, as well as original cross cleats, keep the panel together.
All these techniques have been used by restorers in the eighteenth and
nineteenth centuries to reinforce glued joints (Bünsche 1984:70–74).
Early examples of butterly insert treatments can be found on
panels in the Wallraff-Richartz-Museum in Cologne (Zehnder 1990:198,
inv. 653.223, 67.422, 179). This method was in use around 1900 at the Alte
Pinakothek in Munich. Annual reports describe how butterfly inser ts were
taken out of the structure and the remaining holes filled with putties or
pieces ofwood whose grain was parallel to the grain of the original sup-
port (Kinkelin 1912:fol. 9). Around 1950 setting of butterfly inser ts to rein-
force joints was totally rejected (Wolters 1952:15; Straub 1963:147).
Brachert recommended reinforcing open joints with wooden
strips inserted along the joint; mortises should be made along the joint to
set and glue the strips (Brachert 1955b:21). This method of treatment is
very old and no longer used today.
Around 1950 veneer strips glued across the flow of the grain
across the joints were described. An older technique is to mount very small
wooden blocks over the joints. In the early twentieth century, the annual
reports of the Alte Pinakothek in Munich described how small wooden
blocks could be glued to reinforce joints, to replace the old butterfly inserts
and cross cleats (Kinkelin 1912:fols. 8–10). Some conservators glued these
blocks across the grain, others along the grain (Wolters 1952:15). StraubH P P C A, G, S 225