Series editors' preface - Wood Tools

384 Conservation of Furniture
Signs of structural damage include shrinkage,
distortion, splits, cracks and separation or
loss of components. Structural damage is not
always as readily apparent as the term might
suggest. It may include fine, thin, short, closed
cracks which will open under load but are not
easily seen from normal viewing angles or distances.
It is therefore advisable to check
objects from different angles under varying
degrees of (moderate) applied loads, especially
at or near joints to determine whether the condition
is sufficient to impair function or cause
damage in future. More serious splits, cracks or
distortion may cause varying degrees of impairment
of function, such as preventing drawers,
doors, or falls from working properly. It is
therefore important to check during examination
to see that the object does function as
intended. Since the state of wood is affected by
the prevailing conditions of humidity, this may
be a factor that needs to be considered in relation
to any functional checks. Splits, cracks or
distortion not sufficient to impair function but
liable to cause loss are commonly found in
areas where wood grain of adjacent components
changes direction. This may affect
mouldings on drawers, cross-grained inlay or
other veneer, paint, gilding or other surface
decoration present. Evidence of structural damage
and loss may also include loose, detached
or missing mouldings, (carved) ornament, glue
blocks and metal fittings and fastenings such as
mounts, hinges and locks.
Biological damage includes fungal and insect
attack of various kinds. Absence of flight holes
is not necessarily conclusive evidence of the
absence of an active infestation of wood-boring
insects. Similarly, the presence of exit holes
does not constitute proof of an active infestation.
Ways in which an active infestation can
be recognized and identified have been discussed
in Chapter 7. The condition of the surface
in the vicinity of any holes should be
carefully checked to ascertain the likely extent
of damage and the nature of the treatment
required. Some obvious flight holes but not
sufficient to cause structural weakness or surface
collapse would normally be regarded as
acceptable in older objects containing susceptible
woods such as lime, walnut and elm, particularly
in the sapwood. Surface mould which
could easily be wiped off would also not be
considered serious. More extensive flight holes,
damage round joints or collapse of the surface
might be considered to indicate poor condition.
Active infestation of wood-boring insects
indicated by clean fresh flight holes and fresh
frass or a soft rotten powdery surface with
damage extending below the surface should be
regarded as unacceptable and should lead to
the object being isolated and treated straight
away. The environment in which the object has
been kept should also be thoroughly examined
to determine the source and extent of any
insect or fungal infestation that may be present.
Damages due to chemical reactions in wood
are not commonly observed but some types of
blue–black staining may be caused by interaction
of tannin in wood with ferrous metals or
their salts. Chemical damage to other types of
material, particularly metals and plastics, is relatively
common. Irregular powdery and/or
hard nodular deposits standing proud from the
metal surface are corrosion products. They
may vary from the familiar bright orange rust
of ferrous materials to bright green, turquoise
blue, or dark green powdery spots or patches
of copper alloys. Light grey to white powdery
fils or nodules may be found on lead, zinc, tin
alloys and aluminium and black to blue–brown
deposits are found on silver. Closer analysis of
corrosion products in metals can be very
revealing of the nature of the corrosion process
and the action that needs to be taken to prevent
or reduce further damage.
9.3.3 Methods of examination
It is convenient to distinguish between characterization
and analysis. Characterization relies
on techniques such as gross examination, solvent
testing, examination under low power
magnification, various forms of light microscopy
and alternative light sources. Analysis is concerned
primarily with the identification of
materials. The techniques used to identify nonhomogeneous
and sometimes complex mixtures
fall into two broad classes, spectrometric methods
and separation techniques, principally chromatography.
Together, they provide powerful
tools for the identification and structural analysis
of organic compounds and the qualitative
and quantitative determination of metals and
other elements. The information obtained can
contribute to our understanding of such things
as an object’s age, condition, authenticity and