Series editors' preface - Wood Tools

768 Conservation of Furniture
of water and heat has the potential to cause
thermochromatic discoloration of lacquer
(Webb, 2000). It is necessary to balance consolidant
concentration (degree of adhesion)
against solution viscosity (degree of penetration).
Water-based consolidants, particularly
those based on collagen adhesives, must often
be very dilute (2–5%) and, at this concentration,
may be insufficient to consolidate very
degraded porous grounds. PVAC based consolidants
can offer a combination of good penetration
and adhesion.
Consolidant solutions applied in polar solvents
or water may act as solvent reservoirs
until they have completely dried, leading to
softening or distortion of the lacquer surface.
Where the ground is friable and porous this
may lead to spalling. It is essential to avoid
leaving excess adhesive on the surface when
carrying out localized treatment such as laying
flakes. The conservator should apply pressure,
release it, remove excess adhesive and repeat
this procedure until no excess remains on the
surface.
Shell inlay
The brittleness and translucence of shell inlay
may complicate consolidation. The ground layer
under shell inlay varies in colour and in the
adhesive material used. Many consolidants will
saturate the colour of the ground, darkening it
and changing the colour or reflectance of shell
inlay. The effect of consolidants may be tested
using glass or a facsimile that mimics the colour
of the ground. If it is necessary to add pigment
or filler to the consolidant, matte combinations
will cause the least colour change, but adhere
poorly in the long term. Very dilute animal or
fish glue has been successful in some cases.
16.8.7 Infilling
If an area of loss that exposes the substrate and
ground to the ambient environment is left
unsealed or unfilled it can lead to a continuing
process of adhesive failure and damage to
adjacent areas of lacquer. The use of an inappropriate
fill material can have the same result.
Webb (1994, 1998, 2000) has reviewed the use
of a range of filling materials for lacquer.
Considerations that may influence the choice
of fill materials include the condition of the
surrounding lacquer surface, the sensitivity of
the lacquer to the fill medium, ease of levelling
and possible abrasive effect on adjacent lacquer,
and reversibility or retreatability.
Wax and wax–resin mixtures have been used
as filling materials in the past, when they were
often heated and applied directly into the area
of loss. It has been suggested that, in addition
to the difficulty of removing residues, wax may
migrate into the areas immediately adjacent to
the fill and lead to further adhesive failure
(Nakajima, 1988). Many Eastern and Occidental
lacquer conservators are opposed to the use of
wax as a fill material. Wax fills may be applied
to small areas of damage where an isolating
layer has been used, but should not be applied
directly into a loss from a lacquer surface.
Paraloid B72 bulked out with microballoons
has been used to fill deep cracks and to support
tented lacquer where substrate shrinkage
meant relaying the lacquer flush with the substrate
was not possible (Webb, 1994). PVAL
has been used with some success for filling
losses in the ground layers. Acrylic emulsions
and dispersions may be mixed with an inert
filler to create a reversible fill (see Fill materials,
section 12.3.1).
Two approaches may be useful when filling
losses to lacquer. A filler paste may be made
with minimal solvent and applied in a single
operation. Alternatively, the fill may be built up
in thin layers and allowed to dry before the following
layer is applied. In both cases the
underlying principle is to minimize exposing
the adjacent lacquer to solvent whilst the fill is
drying.
Thermosetting resins such as polyesters or
epoxies may be cast and used as fill materials.
It may be necessary to seal the original surface
to prevent its contamination by the release
agent or the casting material. Such a sealant
should be compatible with the adhesive that will
be used to fix the cast replacement into position.
A volatile ‘binding’ media such as cyclododecane
may prove useful (Brückle et al., 1999).
Materials and techniques used for casting are
discussed in section 10.5. Carr and Driggers
(1997) reported success with the use of silicone
moulds and an epoxy bulked with pigment.
16.8.8 Retouching
Once a surface has been filled, it may be desirable
to match the repair to the existing surface.