Series editors' preface - Wood Tools

568 Conservation of Furniture
difficult to remove all residues. Those that
remain are likely to interfere with the adhesion
of non-wax consolidants, limiting future treatment
to either more wax or a waxy material
such as Beva 371. It has been observed that
waxes can migrate into adjacent porous materials
(e.g. ground layers), disrupting them and
causing further problems.
Beva 371 contains 40% solids (ethylene vinyl
acetate copolymer, cyclohexanone resin, pthalate
plasticizer) in toluene and heptane. It has
a softening point of 50–55 °C and can be
diluted in aliphatic or aromatic hydrocarbon
solvents. When the solvent has evaporated, a
heated spatula can be used to heat-seal the
Beva to the surface. Beva will act as a gap
filler, and any excess on the surface after treatment
can be removed with mineral spirits.
Beva 371 is also available in film form. It is
supplied with two barrier layers that must be
removed before the film is heat-set between
the layers that are being consolidated. When
laying flakes, one barrier layer can be removed
and the Beva heat set onto the substrate. The
second barrier can be removed, the flake positioned,
and a heated spatula used to set the
flake in place. Beva film can be made by the
conservator at a desired strength by casting a
film onto silicone release paper. Beva 371 can
also be used to impregnate a support material,
such as Japanese paper, and allowed to dry.
The Beva impregnated support material can
then be heat set into place or a little solvent
can be brushed onto the surface to activate the
adhesive, or both. Liquid application of Beva
will have a higher bond strength than heat set
film because the liquid will have better penetration
of the substrate.
Collagen adhesives Collagen adhesives, such
as fish glue, gelatin, isinglass and rabbit skin
glue, have many useful properties as consolidants,
ensuring their continued use from antiquity
to today. The coiled helical structure of the
protein chains imparts a degree of flexibility.
Collagen adhesives shrink as they dry, are
hygroscopic, are brittle at low RH and are
prone to mould growth in conditions of high
relative humidity. They are degraded by exposure
to UV and tend to yellow and darken as
they age. Their hygroscopic nature results in
expansion and contraction as RH fluctuates,
and excessively strong solutions have the
(a)
(b)
Figure 12.3 Damage caused by residues of collagen
adhesive
(a) A painted surface with residual collagen adhesive
from a previous consolidation treatment. Residues have
adhered strongly to the paint. Shrinkage of the residues
has caused cracks to form
(b) In places, shrinkage was severe enough to cause
flaking and loss of original paint layers
potential to pull a fragile decorative surface
apart (Figure 12.3). Retreatment with a range of
other consolidants is possible and retreatment
with a collagen glue can reactivate bonding
sites on the original adhesive. They are easy to
use and their mechanism of deterioration is
well understood. Their effective use as consolidants
usually requires that they penetrate a surface
before they cool and gel. For a comparison
of the properties of isinglass, gelatin and rabbit
skin glue see Haupt et al. (1990).
Collagen consolidants are usually applied
dilute (up to c.5% w/v concentration) in a
warmed aqueous solution. The main property