Series editors' preface - Wood Tools

information should always be carefully
recorded before an object is taken to pieces. A
hand-held metal detector is also useful for finding
concealed metal fittings and fastenings.
The overall weight and balance of an object
can help to confirm visual clues about the
nature of materials used in construction and
give a rough preliminary indication of anything
out of the ordinary. If the object seems much
heavier or lighter than might have been
expected from the overall size, shape, construction
and visual clues about materials, it is
important to follow this up to find out why. For
example if the object seems very heavy or out
of balance then perhaps this is accounted for
by an unusually dense timber, or by some hidden
mechanism or structural element of
another, denser material. If the object seems
lighter than one might have expected this
might indicate the use of lower density timbers
(e.g. beech in place of rosewood or veneers
over low density substrates), or of (possibly
concealed) severe insect damage.
It is difficult to use the density of structures
in a precise way but this can provide a useful
means of estimating reduction in strength. Since
for wood specific gravity is the best single predictor
of strength, reduction in density is a measure
of reduction in strength. Density is
calculated as mass per unit volume. Mass can
often be measured with great precision but volume
less so. For some structures it is possible
to calculate volume but for many this is difficult
to do. Measurement of the volumes or masses
of individual components of a structure is best
achieved when objects are disassembled. One
method of obtaining the volume of components
is by immersion (in a suitably protected state)
in a suitable fluid. It should be possible to
demonstrate reduced density of one component
compared to another similar component by its
greater porosity and therefore by increased
fluid penetration and wettability (e.g. by
aliphatic solvents). Reduced density also leads
to more marked deformation under pressure.
The feel of parts moving in relation to one
another under very gentle pressure can provide
useful information about the condition of
joints and in some case even how the piece is
put together. With care some idea can be
gained of stiffness or rigidity and of the
strength of structure while gently testing each
area under compression, tension, bending and
Conservation preliminaries 389
shear, a watchful eye should be kept for signs
of any opening of joints and closed splits.
Particularly when located close to joints, splits
may constitute points of weakness that could
subsequently fail under tension. The object
should be given an all over examination in
which it is subjected to very light loads before
more robust application of any testing loads is
made to determine whether the structure is
strong enough overall for its intended purpose.
This process may sound rather crude and subjective
but with practice it is amazing how
refined a measuring instrument the conservator
can become, applying just enough force to
experience useful feedback about the state of
the object without causing damage. Such techniques
partly seem crude because the measuring
units are not rigorously defined and are
therefore not transferable from one measuring
system (conservator) to another.
During this process of mechanical testing by
the conservator there are other properties it
may be possible to detect. Loose and lifting
veneer and other elements of partially
detached applied decoration will move slightly
under pressure. Lifting areas of veneer also
sound hollow when tapped with a finger nail.
The feel of the surface can also provide important
clues about the types of tools used and the
processes carried out with them. Regular undulations
along or across the grain may indicate
plane marks or turning marks respectively and
it may be possible to pick up by touch other
information about dimensional change and surface
finish.
The hardness (ability to resist indentation
and scratching) and toughness (ability to
deform somewhat without breaking) are interrelated
ideas that can give useful indications of
durability and resistance to wear and hence
about susceptibility to damage from handling
and treatment. Whether or not the surface is
indented by a finger nail can give a rough indication
of hardness. A finger nail will mark
between 3 and 4 Mohs, a needle between 6
and 7 Mohs (for an explanation of the Mohs
scale of hardness see Chapter 10). Probing with
dental tools and the feel of the surface under
gentle pressure may help to indicate condition
of worm damaged timber.
The use of other senses should not be
neglected. Certain materials leave behind characteristic
odours, for example the smell of