Series editors' preface - Wood Tools

306 Conservation of Furniture
tools or poor marking out. The geometry of
the piece may be incorrect, because components
were cut or glued out of alignment,
causing loads to be transferred to parts of the
structure which are not fully able to support
them. Adhesives may have been correctly
chosen but may have been used incorrectly.
Glue may have been allowed to chill off
during assembly or surfaces may have been
inadequately prepared before use or quality
control of materials may have been inadequate.
Inappropriate use may have been made
of screws, nails, or other hardware such as
metal straps and brackets or the wrong
adhesive may have been selected for the
intended service conditions. Even in highquality
pieces, unbalanced construction, for
example the use of veneer or decorative
surface on one side only of a panel, is a
common cause of degradation and failure.
Panels veneered on one side often have a
tendency to develop a concave warp opposite
the veneered surface (Hlopoff, 1978). Applying
gesso or veneer on only one side of a panel
will result in an unequal dimensional response
to changes in moisture content (Buck, 1961).
This is a well-known phenomenon in the field
of panel paintings conservation (Kuhn, 1986).
The same principles apply to decorative
surfaces on wood in furniture where one side
of a panel is treated differently than the other.
Conversely, wooden structures that are
veneered on both sides tend to be less prone
to planar distortion. The benefits of coatings
on both sides of a substrate is illustrated by
the outer panels of triptychs where increased
stability is attributed to sympathetic layering
since both sides are painted.
Poor quality materials used
Wood with one or more of the defects discussed
earlier in this chapter may still have been
included because it was considered too expensive
to eliminate them or because the user was
not aware of them. Animal glue may have been
overheated before use or reheated too often.
Other materials, particularly adhesives, may
have been used past their shelf life or cheaper,
inferior grades may have been selected.
Inappropriate use of material
There may be nothing ‘wrong’ as such with a
material that has been used, it may just be that
it was not the best material to have chosen for
the particular application. An example might
be the use of a timber with large movement
in wide boards. Other examples might relate
to hardness, resistance to splitting, or other
aspects of strength. Traditionally animal glue
has been the furniture adhesive of choice but
with the development of polymer science has
come many new adhesives some of which are
particularly suited to new materials and new
construction methods. Choice of adhesive is
discussed elsewhere but, by way of example,
needs to take account of service conditions,
strength, loading and gap filling ability.
Role of fashion and technical innovation
As new materials, types of construction and
design have been introduced, artists, designers
and makers have had to experiment and learn
how to exploit the strengths and minimize the
weaknesses of a new material or technique.
There is always a learning curve and mistakes
are frequently made during the initial period
of use. This applies to the construction of early
chests, to the introduction of kiln drying, to
the introduction of veneers and to the
manufacture and use of plyform constructions,
for example. In a different sense, fashion plays
an important part in whether things are
accorded a status that helps them to survive.
Conservation treatment errors
The potential for error in conservation is large.
It includes unnecessary additions and removals,
the use of inappropriate or unstable
materials, the use of repairs in which the grain
direction of the wood is wrongly oriented, and
the inadvertent transfer of stress to a weak
member or component of a structure. Treatments
such as butterfly keys, long dowels or
hardware where the intervention restrains the
original wood or other furniture material from
expanding and contracting are a major cause
of failure. Furniture restorers have tried to
reinforce wooden panels by inserting long
dowels perpendicular to the wood grain in the
hope that the panel will not shrink, split or
warp (Sutter, 1986). Another method of
reinforcing repaired splits is to insert crossgrain
‘butterfly’ or dovetail keys (Figure 7.14).
Although the use of butterfly or dovetail keys
dates back as far as the twelfth century, these
inserts cause partial restraint of movement of