Series editors' preface - Wood Tools

when the object is handled. Research on wax
coatings for metal has largely been focused on
outdoor objects that are exposed to weathering,
such as industrial collections and bronze
sculptures (Price et al., 1997; Siepelt et al.,
1998). Selwyn (1990) has observed that
although wax coatings are commonly held to
be easily removed with hydrocarbon solvents,
this may not be true for surfaces that are
porous, pitted, ornate or detailed. It can be
difficult to remove all traces of wax from
crevices etc., and residues may interfere with
the adhesion of subsequent coatings. Moffett
(1996) noted that polyethylene wax could only
effectively be removed using hot xylene.
Shellac has been applied to many metal
fittings and mounts associated with furniture
since at least the mid-eighteenth century
(Dossie, 1758). It has the advantage of being
easy to apply, has very good adhesive properties
and is usually easily reversible in alcohols
such as IMS, ethanol or diacetone alcohol.
Conservators coating boullework have
sometimes used a cellulose nitrate coating
followed by shellac.
Cellulose nitrate (CN) is favoured by many
metal conservators because of its aesthetic
properties. The film is considered very
unobtrusive in contrast with the plastic appearance
associated with acrylics. For many
conservators, this has outweighed the fact that
CN is less than ideal in a conservation context
because it produces nitric acid as it degrades
(Heller, 1983). Advantages of CN include good
levelling and rapid solvent release, which
produces a dry coating within minutes and
reduces contamination from dust. It is comparatively
easy to apply a single coat, which
usually produces a coherent film. Thin coats
may produce a rainbow interference pattern.
Brush application of subsequent coats is often
problematic as lower layer/s are easily redissolved
and subsequent coats usually require
the use of spray equipment. When CN is
applied to a large area it is essential to work
very quickly, though this makes it more difficult
to apply a coating that is even and
without holidays. The use of a proprietary CN
‘pull-over’ solution may allow a brushed or
sprayed surface to be levelled using a chamois
leather and French polishing technique.
Coatings may have a projected lifetime of up
to ten or fifteen years, though cast films kept
Conserving other materials I 687
out of bright light have been reported to have
lasted for over sixty years (Selwitz, 1988).
Aged cellulose nitrate may be somewhat resistant
to dissolution in acetone and removal may
be assisted by extending the contact time via
a solvent gel (Figure 15.8).
Acrylic resins, such as the Paraloids, vary in
their hardness and resistance to atmospheric
pollutants. Thin films are often relatively brittle
(a)
(b)
(c)
Figure 15.8 Removing degraded coating
(a) Detail of the base of a music stand pole, English
c.1810. The coating on the pole was severely degraded
and appeared almost black in places. Swabbing with
acetone was insufficient to remove the coating
(b) Acetone gel was applied to the upper feather and
right hand section of the pole in order to increase the
contact time of the solvent
(c) Base of a music stand pole after removal of gel and
degraded coating. Corrosion pitting was treated with a
combination of mechanical and chemical methods