Series editors' preface - Wood Tools

ise, when making wooden structures, to the
need to use wooden members with the grain
at right-angles to each other. The creation of
strong structures frequently leads to restricted
movement which then leads to damage.
Differences in both the extent and rate of
dimensional response of different components
in the structure sets up stresses that lead to
various kinds of damage. The different hygroscopic
sensitivities of different components of
a structure may be due to the presence of
different materials (e.g. wood, ivory, metal in
a mixed media object), to different species
having been used together, to defects in the
wood or to the way the wood has been cut
or arranged in the structure. Rate of response
to RH changes is also affected by finishes (e.g.
varnish, paint) and by veneers. Compression
set can lead to damage in both large panels
and in joints and all of these factors can
contribute to the damage caused to decorative
structures through differences in the dimensional
response of the support, ground, paint
or other layers. Moisture-induced dimensional
change contributes to adhesive failure and is
frequently a precursor to mechanical damage.
In the absence of stable RH, damage such
as loose joints, splits, checks, and warping may
develop (von Reventlow, 1978; Wright, 1978).
The introduction of central heating systems has
caused damage to furniture and other
woodwork due to the extreme fluctuations in
RH that accompany its use. Before any attempt
is made to treat such damage, however, the
conservator should thoroughly understand the
cause of the problem (Baumeister and Müller-
Amecke, 1989). Splits caused by compression
set, for example, may re-occur if treated by
simply filling the split and assuming that this
will hold the panel together.
7.2.2 Faulty construction and
conservation
Most errors in construction reflect a lack of
understanding of the dimensional behaviour of
wood or occur when such issues were deliberately
subjugated to realize the design. What
may be considered as faulty construction or
conservation may arise because the design
was faulty, or because the execution was
faulty or because poor quality materials were
used. Inappropriate use of material and the
Deterioration of wood and wooden structures 303
role of fashion in design and construction are
two other factors to be considered.
Conservation treatment offers the scope to
repeat many of these errors and to introduce
many new ones.
Design faults
Some examples of different types of design
faults include designs that are not suited to
bear the applied loads, those not suited to
accommodate the movement that would occur
in service and those in which incompatible
materials have been specified in the design.
An example of a design that may not be
suited to bear the loads to which an object
would be exposed in use can be observed in
the short grain of the Regency sabre leg and
scrolled arm. Where such curved structures are
formed by cutting from straight grained timber
there is a section of so-called short grain at
the curve which may be exposed under load
to high shearing forces with a corresponding
tendency to break at that point. Another
example is the architect’s table illustrated in
Figure 7.11 in which the legs have been
tenoned to the drawer front. Dovetail housings
used to attach the drawer sides coincide with
the mortise and tenon joint, exacerbating its
inherent weakness.
Forces acting on the joints of furniture made
with long cabriole legs, where typically no
stretcher is used, may be multiplied by the
effect of leverage and the joint may thereby
be subjected to forces greater than it can
withstand. This is particularly the case when
furniture with this type of leg is dragged along
the floor thereby imposing a sideways force
on the leg which is transferred to the joint.
Deformation of wood can occur through
plastic flow or creep, for example book
shelves can sag under the weight of books,
where the parameters of the design are not
carefully considered.
Well-designed furniture allows for the
dimensional response of wood to occur
without damage. In a frame and panel
construction, the panel should be able to
move freely within the frame, or the panel
may develop splits (Figure 7.12). Thinner
elements, e.g. sides of case furniture, react
more rapidly to changes in RH than thicker
cut sections, such as stile and frame work
(Buck, 1961; Stevens, 1961). Cleats, also