Series editors' preface - Wood Tools

malachite and azurite. Decorative surfaces containing
these pigments should be treated with
pH neutral or slightly alkaline consolidants.
Ideally a consolidant should have a neutral pH
that remains so on ageing, however a range
between 5.5 and 8.0 has been suggested as
acceptable for most artefacts (Down et al., 1996).
Solids content, which describes the proportion
of polymer in a dispersion, can vary from
around 30% to 60%. A higher proportion of
solids will increase gap filling properties,
decrease shrinkage, increase viscosity and
result in harder films. Particle diameter in dispersions
is measured in microns and may vary
from 0.2 to 1 μm. Smaller particle size will
increase penetration of the consolidant.
The properties required of an emulsion or
dispersion will vary with the object being
treated. In general simple formulations of
colourless conservation grade adhesive (i.e.
one whose colour and solubility region do not
shift markedly as it ages), a neutral pH, and a
balance between high solids content and low
viscosity may be suitable for a range of consolidative
treatments.
Poly(vinyl alcohol) Poly(vinyl alcohols)
(PVALs) such as Gelvatol (Monsanto), Mowiol
(Hoechst) and Rhodoviol (Rhône Poulenc),
have been used in conservation as consolidants
and fill materials. Their poor adhesive properties
and a tendency to crosslink and become
insoluble as a result of exposure to UV means
they are unsuitable for many applications. PVAL
was given a Class C rating by Feller (1978), that
is such materials are expected to last less than
20 years with less than a 20% change in properties
such as photochemical stability and solubility
parameters. This classification was broadly
confirmed by Feller and Wilt (1990) in accelerated
thermal ageing tests, however Bicchieri et
al. (1993) suggested that PVAL is not a particularly
unstable resin. The use of PVAL in fills is
discussed below.
Aquazol Aquazol (poly(2-ethyl-2 oxazoline)
has been discussed by Wolbers et al. (1998) and
Shelton (1996). The primary advantage of this
consolidant is its wide solubility range.
Cellulose ethers Cellulose ethers, such as
methyl cellulose and hydroxypropyl methyl cellulose
(e.g. Klucel ® ), have been used as con-
Principles of consolidation, aesthetic reintegration and coatings 571
solidants for decorative surfaces. Their properties
are discussed in section 11.6.2 in the context
of their use as gelling materials. As
consolidants they are usually used in concentrations
between 0.5 and 5% but have been
associated with consolidative failure due to
poor adhesive properties (Stone, 1998). Methyl
cellulose used for consolidation usually
requires low viscosity (e.g. c.330–630 cps for a
2% solution) and low substitution. Cellulose
ethers have been used to consolidate matte
paint, where minimal darkening may be a result
of poor wetting or low solution concentration.
Cellulose ethers with a high degree of substitution
have often been selected as consolidants
because they have increased plasticity and solubility
in polar organic solvents. Feller and Wilt
(1990) found that the long-term stability of cellulose
ethers decreased as the degree of substitution
increased.
Application techniques
The choice of application technique will
depend on the size of the object or the area of
surface that has deteriorated and the nature of
that deterioration. In some cases a consolidant
solution may be brushed on to a surface and
allowed to dry. Excess that has not soaked in
to damaged areas may be removed with a swab
dampened with a suitable solvent. It may be
important when carrying out localized treatment
such as laying flakes or cupped areas to
avoid leaving excess adhesive on the surface,
particularly if the surface is sensitive to the solvent
carrier used for the consolidant. In such
cases the conservator may apply pressure,
release it, remove excess adhesive, and repeat
this procedure until no excess remains on the
surface. Consolidant may be delivered through
facing tissue (see section on Facing below). If
the surface is friable or localized application is
required, consolidant may be applied drop by
drop from a brush of suitable size. Pipettes and
micropipettes can be used for controlled and
localized application of a measured amount of
consolidant. Syringes may be used to inject
consolidant into woodworm exit holes or very
friable substrates. An airbrush may be used to
spray a large area, though the air pressure
should be kept as low as possible. If the surface
is too fragile for brush or spray application
it may be possible to utilize an ultrasonic mister
(Michalski and Dignard, 1997; Michalski et