Series editors' preface - Wood Tools

minium triformate or aluminium alkoxide.
These salts were used to saturate the flesh
(underside) of the leather. Because aluminium
sulphate and aluminium triformate were added
from aqueous solutions, the benefit of the salts
on the leather was often outweighed by the
damage caused by the water carrier.
Aluminium alkoxide, however, is applied in a
non-polar solvent carrier and is therefore
inherently safer. There have often been unrealistic
expectation of what can be achieved
using such treatments, which can stabilize pH
and the chemical deterioration of the collagen/tannin
complex, resulting in a significant
increase in shrinkage temperature. The
mechanical properties of the leather, however,
remain unchanged. Success is somewhat
dependent on operator skill and treatments
have caused surface darkening of the leather.
Accelerated aging experiments have suggested
that retanning treatments may exacerbate deterioration
in the long term (Larsen et al., 1996).
Consolidation
Leather that is powdery or flaking may require
consolidation. Whilst maximum penetration of
consolidant into the leather is desirable to prevent
later delamination, it has been suggested
that the maximum average penetration of a
consolidating material is approximately 50% of
the thickness of the leather. Penetration will be
assisted by the use of dilute solutions and low
molecular weight and small particle size.
The fundamental principle of the consolidation
of leather is to avoid solidifying the structure
of the leather. This means that many
common conservation consolidants are inappropriate.
Paraloid B72, for example, saturates
and darkens the surface of the leather and has
a solidifying effect on the structure. Other
resins with a glass transition temperature (Tg)
higher than the ambient room, display or storage
temperature are similarly inappropriate.
Although cellulose ethers such as Klucel ® have
been used in the past because they do not
darken abraded leather, they are no longer
widely used because they are comparatively
chemically unstable and there are better alternatives
for the consolidation of leather.
Ideally, consolidants for leather should have
a Tg around room temperature for maximum
flexibility, a pH in the range of 5.5–8, though
within this range adhesives with a higher pH
(a)
(b)
Conserving other materials II 733
Figure 16.7 Application of consolidant from a pipette
(a) on a nineteenth century shoe from Northampton
Central Museum and using a heated spatula (b) to heat
set the consolidant
may be more appropriate. Adhesives should
exhibit minimal or no off-gassing of volatile
acids or alkalis and minimal or no yellowing
on ageing. Flexibility is more important than
strength for the consolidation of leather. PVAC
adhesives generally have a lower, more acidic
pH than acrylics and may off-gas acetic acid for
up to a year. PVAC adhesives are generally
stronger and less flexible than acrylics (Down
et al., 1996). For these reasons acrylics emulsions
and dispersions are usually selected for
the consolidation of leather. Although as a general
rule aqueous adhesives should be avoided,
acrylic emulsions and dispersions may be used
if diluted (1:2 to 1:3) in a compatible non-polar
solvent.
Lascaux 360 HV has been used to consolidate
leather. It is a butyl acrylate (>50%)/methyl