Series editors' preface - Wood Tools

766 Conservation of Furniture
circular motion across a small area (a square
inch or so) of the surface. As solvent diffuses
into the resin coating it will start to swell and
may blanch (become white). Continued treatment
with very light pressure will remove the
coating. This technique requires caution and
patience. All the solvents mentioned above can
damage lacquer if used insensitively and, even
if a particular solvent is successful, this is a
time-consuming process.
Non-drying oils such as almond oil can be
removed with white spirit. Coatings of a drying
oil or oil–resin varnish may be problematic.
Removal of linseed oil, for example, usually
requires polar solvents, elevated pH or
enzymes. Polar solvents and elevated pH may
cause significant damage to the underlying lacquer
surface, depending on its condition.
Michalski (1990) has tabulated data on the
swelling effect of some solvents and solvent
blends on linseed oil films. The use of a lipase
treatment is dependent on the sensitivity of the
underlying lacquer to aqueous solutions, and
whether the enzyme can function at a pH that
will not damage the lacquer.
16.8.6 Consolidation
Separation of upper layers from lower foundation
layers is perhaps the most common consolidation
problem that will be encountered on Oriental lacquer
objects. This is most often a result of
environmental conditions, particularly low or
fluctuating RH, or the original manufacturing
technique. Protein adhesives such as animal glue
or animal blood were used in some foundation
layers. Grounds based on clay and animal glue,
typical of Japanese Meiji period (1868–1912) lacquerware,
are comparatively weak and often fail.
In the case of lacquer-based foundation layers,
the amount of lacquer binder used at the time of
manufacture was often reduced to speed drying.
As the object ages, however, insufficient binder
can lead to detachment between upper layers
and foundation, and between foundation layers
and the substrate (Minney, 1999).
Consolidation of lacquer can be undertaken
using lacquer-based materials or synthetic
resins. Lacquer-based materials, which
crosslink, are irreversible. Synthetic resins
applied to a porous and fragile substrate or
layer offer the advantage of retreatability and a
degree of reversibility.
Softening brittle lacquer before
consolidation
Cups, blisters or flakes on an Oriental lacquer
surface are often brittle and may require softening
before consolidation can be undertaken.
Humidification, heat and the use of polar solvents
may soften lacquer sufficiently to allow it
to be relaid flat onto the substrate.
Humidification at around 70% RH is often
effective for softening brittle lacquer. A Gore-
Tex sandwich may be useful for localized
short-term humidification (see section 15.2.2).
Humidification for an extended period, e.g.
one to six months, may be necessary, depending
on the thickness of the lacquer and the
nature and thickness of the substrate. The traditional
method for humidifying lacquer furniture
is to use a wooden box, though polythene
or Perspex may be substituted. If wood is used
for a humidification box, the conservator
should be aware of the acidity of the wood and
its potential for off-gassing volatile organic
acids, particularly acetic acid (Table 10.1). Such
off-gassing increases as temperature and RH
increase, and will damage many metals used
for decorative inlay. Consideration should be
given to the long-term effect of humidification
on the substrate. Humidifying lacquer furniture
that has been stored or displayed in an environment
with low RH may be problematic. If a
wooden substrate has split, for example, a sustained
cycle of high RH, followed by a return
to ambient low RH conditions can exacerbate
compression set. It may also cause additional
stress on the lacquer or ground that has been
consolidated.
Heat can be used to soften and ‘relax’ distorted
lacquer but as the lacquer cools it usually
resumes the distorted shape. A heated
spatula, isolated from the surface with silicone
release paper or Melinex/Mylar, may be used
to apply heat (c.55–60 °C) to a small localized
area. Short exposure to heat may be insufficient
to soften the lacquer. Webb (1995)
described the use of a thermal sheet in combination
with weights, applied over a period of
several days, to flatten distorted lacquer. The
combined use of heat and moisture has the
potential to discolour lacquer. Webb (2000)
reported that the combination of moisture and
heat as low as 50 °C from a spatula could result
in a colour change on the surface of light-damaged
lacquer.