Series editors' preface - Wood Tools

586 Conservation of Furniture
whilst high molecular weight resins might be
used at a 10–30% w/v concentration, or for texturing
fills a 50% w/v concentration may be
useful. When the resin has dissolved, the solution
can be used to make tablets of colour.
To make paint tablets, take some of the resinin-solvent
mixture and add pigment. Use an
artist’s palette knife on a flat surface (or a
muller and slab) to work the pigment evenly
into the resin, breaking up lumps to make a
smooth paste. Add this mix to the main resinin-solvent
mixture, repeating the process until
enough pigment is dispersed to create an
opaque paint. Pigment particles vary in shape,
size and polarity and thus the amount of
medium they absorb. These differences will
affect the pigment to binder ratio, as well as the
gloss and final texture of each paint (Leonard et
al., 2000). It may be desirable for tablets to be
slightly underbound rather than resin rich
because it is easier to add gloss than take it
away. Retouching is a dynamic process and the
conservator usually has to judge the ratio of
pigment, diluent and medium as they work, on
the basis of the saturation and gloss that is
required in each instance.
Resins in solution tend to deteriorate much
faster than those in solid form. Once the paint
has been made, it can be poured off into a container,
the solvent allowed to evaporate so that
the paint forms a solid block, and the container
then sealed. At the beginning of the retouching
session, a small amount of solvent is added to
the tablets to produce a workable paint.
Alternatively, paint can spread on a sheet of
Melinex/Mylar. Once dry, it can be broken into
flakes and stored in a container ready for use.
Commercial preparations
Some conservators prefer to use pre-mixed proprietary
materials that offer the advantage of
finely ground pigments well dispersed in a
binding medium. Le Franc & Bourgeois
‘Charbonnel Restoring Colours’ are based on a
mixture of ketone and acrylic resins (poly
isobutyl- or poly n-butyl acrylate) in a hydrocarbon
solvent. The potential crosslinking of
butyl acrylate means that these retouch materials
should be applied over a reversible isolating
layer. Maimeri ‘Restauro Colours’ have a marked
tendency to discolour as a result of the mastic
binder but give excellent saturation, particularly
of dark colours. Bocour ‘Magna’ paints, based
on a poly(n-butyl methacrylate) medium, are no
longer available. Golden ‘Polyvinyl Acetate
Conservation Paints’ contain pigment ground in
a PVAC binder. Gamblin Conservation Colours
are based on Laropal A81, a photochemically
stable urea formaldehyde resin. Artists ‘Acrylic’
colours are readily available and easy to use but
there is a colour shift as they dry and they tend
to become darker as a result. De la Rie et al.
(2000) found that retouch paint based on
Paraloid B72, PVAC or Laropal A81 resins
offered the best photochemical stability.
12.4 Coatings
12.4.1 Introduction to coatings
Coatings applied to furniture and other decorative
art objects perform a dual aesthetic and protective
role. Transparent coatings saturate the
colour of the wood or decorative surface, offer
some protection against accretions of dirt and
grime, and can slow the permeation of atmospheric
moisture and pollutants. A coating
applied in the course of a conservation treatment
must balance these functions with the additional
constraints imposed by conservation ethics.
Aesthetic considerations usually require a transparent
coating that saturates the surface. The
protective function requires a coating that will
allow dust and other accretions to be removed
without damaging the surface below.
Permeability to moisture and pollutants varies
widely according to coating type and thickness
(Schniewind and Arganbright, 1984; Brewer,
1991). Conservation ethics require a coating that
resists photochemical degradation (e.g. oxidation,
yellowing, crosslinking) and allows removability
without damaging the substrate. It may be
necessary to consider the shrinkage stresses that
the coating will cause (Whitmore et al., 1999). In
some cases application of a coating may not be
appropriate. For example, a painted surface
characterized by high pigment volume will
appear matte, and application of a varnish may
completely and irrevocably alter its appearance.
In the context of furniture, hardness may be
an additional coating consideration. Although
there has historically been some overlap
between the coatings applied to furniture and
painted surfaces, a distinction is necessary
between surfaces that are essentially decorative