Series editors' preface - Wood Tools

that which occurs during the removal of varnish
with solvents. Although solvent evaporates
from the surface of an applied varnish
coating, it also diffuses into the underlying
paint film and will dissolve soluble components,
carrying them into the varnish layer as the
solvent diffuses through it and evaporates.
Tsang and Erhardt (1992) demonstrated that
the amount of leachable material found in varnish
after only several days of drying was comparable
to what would be extracted from the
paint during solvent cleaning. Thus the selection
of solvent used to apply varnish is as
important as the choice of solvents used in
cleaning. The bulk of solvent will evaporate
out of the varnish film relatively quickly, but a
small percentage will be retained and released
slowly. The rate of release will depend on the
chemical affinity between solvent and polymer
and the stereochemistry of the solvent molecules
– small linear unbranched solvents molecules
will be retained least by a polymer film
(Newman et al., 1975). Films of Paraloid B72
retain a significant amount of toluene, for
example, for many months. In comparison, pxylene
evaporates more slowly during the initial
drying stage but is not retained by the B72
in the later stages (Dauchot-Dehon and De
Witte, 1978).
Sutherland (2000) found that the leaching
effect of a varnish solution on an oil paint film
depended on the polarity of both the solvent
and the resin component/s of the varnish. Of
the resins tested, he found the following order
of leaching effect: dammar > MS2A > Paraloid
B72 > Regalrez 1094. He suggested this order
was a result of polar functional groups, e.g.
hydroxyl, carbonyl and carboxylic acid groups,
contained in the structure of the resin. The use
of a varnish composed of non-polar solvent and
resin is indicated in cases where a painted surface
has exhibited sensitivity to polar solvents.
16.6.8 Matte paint
Matte paint is characterized by a high pigment
volume concentration (PVC). In other words,
matte paint contains a high proportion of pigment
and comparatively little binder. The treatment
of matte paint has been considered by
Feller and Kunz (1981), Hansen, (1990),
Hansen and Bishop (1998), Hansen et al.
(1993), Hansen et al. (1994) and Welsh (1980).
Conserving other materials II 753
Cleaning matte paint is often problematic
because the underbound paint surface may be
damaged by contact with a swab or other cleaning
tool. Consolidation is often required before
cleaning can be undertaken. Consolidation is
complicated by the fact that the surface of the
paint is often characterized by voids between
the pigment particles that are not filled by
binder. If the consolidant fills these voids, some
change in appearance is inevitable. The degree
of change will in part depend on the amount of
consolidant added and its distribution within the
paint layer (Hansen, 1990). As a general rule,
the darkening effect of a given consolidant can
be minimized by using low concentrations
(< 5%) in a slow-evaporating solvent that prevents
reverse migration and deposition of consolidant
on the surface. Thus Welsh (1980)
reported success using a 4% solution of Paraloid
B72 in diethylbenzene. Application techniques
such as ultrasonic misting of aqueous consolidants
with a concentration as low as 0.5% will
prevent the treatment physically disturbing the
surface and can minimize darkening as a result
of consolidation (Michalski and Dignard, 1997;
Michalski et al., 1998).
The application of a coating to matte paint
surfaces should be considered on a case-bycase
basis but is usually inappropriate. In some
cases the original decorative effect exploited
differences in matte and gloss, for example
chairs decorated as part of an overall interior
scheme may contrast areas of matte paint with
adjacent areas of highly burnished water gilding.
It may be possible to apply a micro-thin
coating using spray application that does not
disrupt such original intent, or an aesthetic that
accurately represents age and use. As a general
rule, however, coatings will tend to fill the
voids between the pigment particles and saturate
the appearance of the surface.
16.7 Japanned furniture
16.7.1 Introduction to japanning
Japanning is a comparatively non-specific term
and, in its broadest meaning, can encompass
any surface finish produced in the West that
approximated the appearance of Oriental lacquer,
known in Japan as urushi. The conservation
treatment of japanning is quite different