458 Brewer
have been about 140 kg.^21 Painted in portrait format, the substantial
remaining weight and reduced thickness have had serious consequences.
The most recent conservation treatment, carried out in the 1960s,
included thinning and reinforcement with a balsa laminate similar to that
described by Lucas (1963). Subsequently, metal strips were added around
all edges. Many of the panel’s original joints later parted, presenting a
precarious structure and dismembering the image both literally and
figuratively. Structural damage made reappraisal of the painting’s con-
dition necessary as well, despite its recent restoration.
In contrast, a painting of 1537 by Marco Palmezzano (ca. 1458–
1539) (Fig. 4a–c) with a lower-density poplar construction (briefly
described above) arrived with the image greatly obscured by darkened
varnish layers and surface dirt.^22 Weakened in areas by insect damage,
thispanel had also been thinned to about half its original thickness,
which weakened it further. A lattice of wood had then been glued to
it, probably before it left Italy.^23 Undulations and compression damages
attested to poplar’s high capacity for bending and distortion under
mechanical stress. Fortunately, the painting exhibited sound technique,
a great advantage for structural conservation.^24
Both panels were assembled with casein glue. The joints of the
Palmezzano had remained intact under stress, while the weaker, fibrous
wood had parted into disconnected intermittent splits. Under stress, the
stronger and more rigid walnut of the Mengs had remained relatively
intact, while the joints had parted in the glue layer. These differences in
fracture characteristics were due in part to the varying restraints imposed
by the auxiliary supports. The wood of both paintings had fractured pref-
erentially in insect-damaged areas.
More than thirty splits had developed throughout the
Palmezzano, mainly from movement-restricting battens glued to the back.
Some splits were older, with putties and aged varnish in the gaps, while
others were obviously recent, with freshly exposed and fractured ground.
What factors led to deterioration of these panel paintings? Both
panels may be examined more closely to understand the effects ofstruc-
ture, age, and past treatments on their condition.Supports
The Mengs consists of six broad walnut planks arranged horizontally with
respect to the image and joined in reverse orientation (Fig. 9d).^25 The bot-
tom consists oftwo additional pieces: a narrower plank at the extreme
edge, joined to a narrow, wedge-shaped strip. The wedge was used to
square the bottom edge in relation to the taper of the lowest broad plank.
At the extreme top edge, there is a similar narrow plank but no wedge.
Evidence shows that the panel was originally about 40 mm thick,
twice its current thickness. The mortises and loose tenons had been
uncovered by modern tools during the most recent thinning. The mortises
had been chiseled into the joint faces to within 8 mm of the front of the
panel^26 so that if originally centered, they would have left the same thick-
ness of8 mm at the back. The tenons^27 were not butterfly inserts, set into
sockets cut into the panel back, as a superficial assessment of the exposed
panel back might suggest. Thinning had also exposed remnants oforiginal
nails driven into the top and bottom edges, probably to secure the strips.
These would have been driven near the center line of the original edges.