Series editors' preface - Wood Tools

730 Conservation of Furniture
and with hot water and a sponge wash the
cane-work so that it may be thoroughly soaked.
Should it be dirty, use a little soap, let it dry in
the air, and it will be as tight and firm as when
new, provided the cane be not broken.
Such treatment of plant material in historic furniture
is inappropriate because it may be too
weak to withstand the stress caused by tightening
as it dries. Reshaping using rehumidification
may be possible but differential
shrinkage, staining or colour loss may occur.
Previous ‘maintenance’ treatments, such as
annual oiling, coating with shellac, other varnishes
or paint may have been undertaken to
allow the surface to be easily wiped down. On
balance, there is no evidence that these treatments
did any good and they may have caused
harm in some cases. Such coatings may preclude
humidification treatments.
Plant materials may be humidified by a variety
of techniques including contact humidification,
misting with a spray or ultrasonic
humidifier, by enclosing the object in a humidity
chamber or the use of moisture-permeable
membranes such as Gore-Tex (Britton, 1994;
Doyal, 1999). ‘Contact’ humidification involves
sandwiching the object between layers of wet
and dry materials to elevate humidity without
saturation or direct contact with water. The
bottom layer of the sandwich may contain wet
linen or damp acid-free blotting paper over
which are placed at least six layers of dry linen
or acid free blotting paper. The object is placed
on top and a spacer layer is suspended over
the object. A layer of polythene sheet is placed
over the top to contain the humidity, which
rises through the object. The spacer layer,
which may be acid-free tissue or a permeable
membrane such as Gore-Tex or Sympatex,
stops the polythene from coming into contact
with the object and prevents any condensation
that may form on the polythene from dripping
back down onto the object.
A humidity chamber can be a simple polythene
tent or a purpose-built climate chamber.
Water or a range of conditioned gels or buffering
agents can be used to increase control of
humidity changes around the object.
Deacidification
As with other organic materials, cellulosic
materials become more acidic in time. There
may be concerns that excessive acidity can
lead to accelerated autocatalytic degradation
and conservators may wish to measure pH.
The standard method for measuring pH
requires maceration of a sample in water. In
cases where destructive sampling is not acceptable,
a drop of distilled water may be applied
to a dust-free surface. A non-bleeding pH
paper may then be applied, weighted (e.g.
with a glass plate) and left for a few minutes.
Although this is not a very accurate method it
can be a less intrusive alternative to destructive
sampling. A pH of 3 or below might be considered
a problem, as may a slightly less acidic
pH that is associated with embrittlement. If a
small test deacidification provided an increase
in flexibility, overall deacidification may be
appropriate. Deacidification need not necessarily
be undertaken for its own sake.
Deacidification of plant materials has been
achieved in some cases by washing in water,
application of neutralizing buffer solutions by
spray or immersion, exposure to alkaline
vapours, or by the use of particulate alkaline
buffers that are then brushed and vacuumed
away. All of these treatments should be
approached with extreme caution and may
cause darkening of plant material.
Repair
Techniques used to repair plant materials are
often based on techniques of manufacture, for
example, patching with new material. Other
techniques rely on mechanical (stitched) or
adhesive repairs. These can include sandwiching
the original between two layers of semitransparent
fabric stitched around the breaks.
16.3.10 Imitation leather
Imitation leather, often called leatherette, is
often based on vinyl polymers. Thorp (1990)
has considered its structure, composition and
conservation treatments. Previous repairs to
this type of material may have encompassed
the repair of cigarette burns, cuts, tears and
surface abrasions. Repairs may have been
undertaken using proprietary kits based on a
thermoplastic resinous filling, textured when
still soft using grained papers. This technique
may be adopted by conservators using
reversible materials.