Series editors' preface - Wood Tools

576 Conservation of Furniture
to the loss, it ensures that all restorative work
is isolated from the original. Pre-varnishing also
prevents ‘ghosting’, which often occurs if the
area surrounding the fill is unvarnished and
dust created when a fill is levelled becomes
lodged in cracks and other interstices.
Filler should ideally never cover original decorative
surface. Fills should be reversible without
damage to, and ideally have a lower
modulus of compression than, the original
material. The inclusion of X-ray dense barium
sulphate has been suggested as a means of tagging
gesso fills, although the possibility that this
may obscure constructional information below
should be considered (Thornton, 1991a,
1991b). Unlike other compounds of barium,
which are highly toxic, barium sulphate is
chemically inert and may safely be used as a
bulking agent (Thornton, 1998). Other
approaches include the addition of a small proportion
of pigment so that a restoration fill can
be distinguished from adjacent original material.
Documentation should include an accurate
record of the extent of repair.
Many conservators isolate a fill from original
material using either a collagen adhesive or a
synthetic. Collagens may not be easily distinguished
from original material whilst synthetics
may interfere with the absorptive properties of
the ground. The area to be filled should be
cleaned and sized to reduce porosity and
ensure a good adhesive bond for the fill. A
gesso type fill may be built up in stages to prevent
excessive shrinkage. Dried fills can be levelled
using a scalpel, with a damp swab,
abrasive paper (taking care not to touch the
original surface) or with a suitable solvent. Fills
may be textured with tools such as scalpels or
swab sticks or by pressing a mould prepared
from the original surface into the fill whilst it is
still slightly damp. Leaving fills untextured can
be a way of ensuring that repairs are identifiable
but not obtrusive. The quality of the fill
defines the quality of the finished repair. No
amount of expert retouching will conceal a
poorly executed fill. Information on casting fills
for large areas of loss can be found in section
10.5.
As with consolidation, adhesives in fills are
usually used in dilute concentrations. Collagens
have been utilized in concentrations between 2
and 5%. They are easy to manipulate when wet
and are easy to level after drying. Animal glue
bound fillers are prone to shrinkage as they dry
and are unstable if exposed to fluctuations in
RH. Other adhesives such as methyl cellulose
and Paraloid B72 may also be used as the
binder in fills. PVALs and PVACs have been
used between 5% and 15% concentration.
Synthetics may provide a better adhesive bond
to the substrate. A few drops of PVAC added to
a collagen gesso, for example, will often
improve adhesion, inhibit gelling to allow the
fill to be worked longer, and may impart easier
reversibility. If adding resin in this way, it is
important to be aware of the overall proportion
of resin in the fill after volatile solvents have
evaporated. One way to conceptualize this is to
consider the traditional practice of adding 10%
v/v linseed oil to a natural resin varnish composed
of, for example, 30% w/v resin dissolved
in solvent. Although the oil composes only 10%
of the varnish solution, when solvent has evaporated
off the proportion of oil will in fact be
25%. The same principle applies to the addition
of synthetic resins to a fill mixture, which can
result in an unintentionally hard fill.
Small areas of woodworm damage can either
be accepted or filled and retouched. In the case
of a large number of exit holes, it may be desirable
to clean the exit holes to a depth of one
or two millimetres and fill them with a neutralcoloured
filler. Though often used for wood, as
a general rule the use of wax-based materials
should be avoided on decorated surfaces. Care
may be needed to ensure that the overall effect
is in balance with the colour and appearance of
the surface.
Fill materials
A combination of adhesive and an inert filler
with the possible addition of a colorant can be
used to repair losses. The adhesive component
can potentially be any of the materials discussed
as consolidants above. Factors that will
affect the properties of fills include the degree
of secondary molecular bonding between
adhesive and filler, the percentage concentration
of the adhesive solution and the proportion
of filler that is added to it. Considerations
for filling materials include how well the fill
adheres to the surface, the amount of shrinkage
that occurs as it dries, the elasticity of the fill,
the length of time it takes to dry, how easy it is
to level the dried fill and reversibility/retreatability.
The flexibility of the fill should be a prop-