Series editors' preface - Wood Tools

758 Conservation of Furniture
surface between layers. Sometimes the clear
varnish applied over the painted or gilded decorative
layer is the one to separate. The
approach to consolidation must take into
account which layer of the japanned object is
in need of consolidation.
Collagen glues such as rabbit skin glue,
gelatin, or fish glues have been traditionally
used in the repair of japanned objects when
the gesso ground layer has delaminated from
the substrate. The glues penetrate to the
ground well, and since they shrink as they dry,
the bond between the lifting flake and the substrate
is quite good. However, water-based
adhesives may cause blooming of the varnish
layers. The risk of bloom increases as the pH
of the adhesive rises, or with prolonged exposure
of the surface to heat and moisture.
Solutions from 2% to 5% have been used to
successfully consolidate japanned ground layers.
Different protein based glues can be used
for different objects. Paler adhesives such as
isinglass or gelatin can be used enough to consolidate
light japanned pieces, where there is a
danger that darker collagen adhesives may
cause a colour change.
Synthetic adhesives such as emulsions or dispersions
based on PVAC or acrylics are discussed
in section 12.2.4. If such materials are
used to consolidate the ground layer, the particular
adhesive should be chosen with particular
attention to long-term stability and
flexibility. Acrylics are generally weaker and
more flexible than PVAC (Down et al., 1996)
and may therefore be more appropriate in this
context. Resolubility is also an important consideration.
Ideally the dried consolidant should
be resoluble in a solvent that does not affect
either ground or varnish layers, such as aromatic
hydrocarbons. Those that are resoluble
only in water or very polar solvents such as
acetone are inappropriate for use on japanned
surfaces.
Paraloid B72 and Paraloid B67 have been
used successfully over the past few decades in
the consolidation of japanned surfaces and are
a popular choice because of their excellent
ageing characteristics. These are best used for
separation between the varnish layers. Paraloid
B72 should be used in situations where it is not
left on the surface because it can impart an
unnatural plastic appearance. Paraloid P67 has
an appearance closer to those found on japan-
ning. Since both B72 and B67 can be dissolved
in a number of solvents, it is possible to
choose a medium that does not affect the surface.
Hydrocarbon and aromatic solvents are
good choices. When mixing either acrylic, the
percentage should be kept fairly low. Several
applications of 2% are better than a single
application of 10%. The low concentration will
aid penetration and prevent an unnecessary
build up on the surface. Ideally one should
have little or no consolidant remaining on the
surface.
16.7.6 Infilling
Fills for grounds
When filling losses to japanned surfaces it is
better to consider the ground layers and the
varnish layers separately. To ensure reversibility
of any of the fills listed below one should
isolate the substrate from the fill with a readily
soluble material before proceeding. One must
remember that the fill should be weaker than
the original surface. Should the wooden substrate
move, it is better that the fill fall out than
cause more damage to the original surface.
Traditional gesso fills of rabbit skin glue and
calcium carbonate are appropriate for the
ground layers since they are similar to the original.
Barium sulphate can be added to the
gesso to ensure that the fill can be identified as
non-original. Before filling, the area surrounding
the loss should be consolidated and the
surface protected with a removable varnish. A
very weak pigmented gesso can be used for a
very fragile surface with numerous losses
(Ballardie, 1994). For deeper losses, gesso
dough is preferable to several applications of
liquid gesso. This prevents the damage to the
japanning from excess exposure to moisture.
The combination of PVAL and whiting can
be used instead of the traditional rabbit skin
glue gesso. Since the PVAL can be applied easily,
dries fast and also can be burnished to a
very smooth finish, it seems a good candidate
for use as a fill in japanning (see section
12.3.1). As with any fill material, care should be
taken not to expose the surface of the japanning
to this material. Webb (1998a) reported
the use of 6% PVAL in water, whiting and dry
pigments to infill losses on a late seventeenthcentury
cabinet in the Royal Ontario Museum
collection.