Series editors' preface - Wood Tools

734 Conservation of Furniture
methacrylate copolymer. Butyl acrylate/methyl
methacrylate copolymers with a higher proportion
of butyl acetate produce weaker but more
flexible films. Lascaux 360 HV has a slightly
alkaline pH (c.7.8) which, after four years of
dark ageing, dropped to c.6.7, and thus fell
within limits defined as acceptable by Down et
al. (1996). Lascaux 360 HV did emit a small
quantity of acetic acid and freeze/thaw cycling
will cause the emulsion to collapse. Even
though it has a Tg of –8 °C, 360 HV is very flexible,
with 1000% elongation at break.
Pliantex has been widely used for the consolidation
of archeological leather because it
produces a soft film, is flexible (410% elongation
at break) and does not crosslink (Figure
16.7a,b). It is an ethyl acrylate/methyl methacrylate
copolymer (> 66% ethyl acrylate) solution
in organic solvents. Tests by Down et al.
(1996) indicate it is significantly less flexible
than Lascaux 360 HV, and after dark ageing for
four years pH had dropped to c.5.
Infills
The materials used for infilling losses partly
depend on the size of the loss. Large areas of
loss are often replaced with leather whilst
smaller areas often use polymeric materials.
Leather infill techniques Semi-alum leather,
that is leather which has been vegetabletanned
and then retanned with aluminium
salts, is often the best option and is suitable for
general repair work. Chromium tanned leather
may offer the advantage of durability and is
generally softer and more flexible than semialum
leather. It has different flexing characteristics
to the original, however, and is generally
much more difficult to pare and manipulate.
Vegetable tanned leather is not usually considered
chemically stable enough for repairs
unless it has been retanned. The skin type and
grain of the leather used in the infill should be
matched as closely as possible to the original,
although it is often difficult to match the texture
of the original exactly.
Four methods of infilling with leather are
illustrated in Figure 16.8. In all cases the
leather is glued into position. In cases where
the leather must be able to flex, a good adhesive
bond on leather requires limited penetration
of the adhesive into the nap. Deep
penetration will reduce the flexibility of the
Grain
Flesh
(a)
Grain
Flesh
(b)
Grain
Flesh
(c)
Grain
Backboard/support
(d)
Beva film and
support fabric
Figure 16.8 Four methods of infilling with leather: (a)
a stepped infill; (b) an overlapping in situ leather fill;
(c) a skived infill, which has better visual and structural
properties than a stepped infill (a): thin skived infills
can be strengthened with a backing fabric; (d) a plug
infill. In cases where the leather is supported by a solid
backboard (e.g. chests or panels), the infill can be
adhered to the backboard or support
leather. Stepped or overlapping in situ fills may
add undue bulk, particularly for leather
adhered to wood, e.g. writing surfaces. Skived
or plug infills require the use of a thin flexible
support fabric.
Unfinished leather, buff in colour, has not
been glazed or dyed and is therefore easier to
colour match. Leather may be coloured using
azo metal complex dyes (available through the
Leather Conservation Centre, UK). These dyes
are water-soluble, light-fast and formulated for
use on leather. The dyes are supplied in four
colours (blue, brown, yellow, and red) that are
mixed as required.
Adhesives for leather infills Protein-based
glues are generally inappropriate for leather
because of their moisture content and because
most are applied hot. Shrinkage temperature
may be lower than expected in untanned or
aged and degraded leathers and exceeding the
shrinkage temperature will cause irreversible
damage. Future removal of collagen adhesive
may be problematic, particularly in the light of
the need to minimize contact between old
leather and water.
Acrylic emulsions and dispersions are usually
selected for the consolidation of leather
(see discussion of consolidation below). Selm