Series editors' preface - Wood Tools

the structure of the lacquer film and that internal
stress develops in the film on water desorption.
Loss of bound water leads to progressive
deterioration of the lacquer film including loss
of flexibility and toughness (hence an increase
in brittleness) and changes in the barrier
properties to water and oxygen. However,
excessively high levels of RH may actually
promote oxidative degradation of the film by
enhancing oxygen transport. This highlights the
need to know what is happening to both
objects themselves and to their environments.
In the typical case of lacquer on a wooden
core, RH changes could lead to a variety of
different types of loss of structural integrity of
the film including cracking, splitting, delamination,
or warping. The outcome depends on
various factors such as the moisture vapour
transmission rate of the lacquer, the strength
and elasticity of the lacquer film, the moisture
content and plasticity of the core, the adhesion
between the various layers and the different
types and amounts of movement. Once the
structural integrity of a lacquer film is disrupted
there is greater potential for much more rapid
deterioration. This is recognized in Japan where
great concern is shown to preserve the structural
integrity of lacquer films at all costs and
to maintain appropriate levels of RH to do so.
When an object has been made and subsequently
kept under particular conditions this
may seem the best course of action. It is less
clear for objects that have been in much lower
average relative humidity conditions in Western
collections for many years whether it would
now be appropriate to significantly raise the RH
of their environment. This needs to be
approached cautiously beginning when RH
indoors is naturally high (i.e. the summer) and
aiming to reduce the extent of winter heating
and the accompanying drop in RH.
The best lacquer prepared from the best
quality materials, carefully crafted and well
cared for, will survive for centuries. On the
other hand examples of export lacquer hastily
prepared from inferior quality materials may
exhibit the most horrendous problems of
cupping, delamination and embrittlement. From
measurements of the dynamechanical properties
of sap and lacquer films it has been
demonstrated that films prepared from sap
undergo a large degree of crosslinking during
their first three years but that carefully prepared
Deterioration of other materials and structures 343
lacquer films keep almost the same degree of
crosslinking during this period (Kuwata et al.,
1961). Moreover, further work by Kumanotani
(1981, 1983) shows that lacquer films stored
over twenty years change very little.
Comparison of the density of sap and lacquer
films stored for nineteen years shows almost no
variation in density for lacquer films but a
remarkable change for sap films.
Some very real practical measures can be
adopted to help reduce the risk of handling
damage to which lacquer is likely to succumb
following the damage caused by exposure to
light and low RH. In general this means following
carefully the precautions outlined in
Chapter 6 (section 6.2.7). In particular, lacquer
objects should not be stored close together
unless individually protected to prevent
accidental contact with other objects during
handling. Always remove jewellery before
handling lacquer, wear moisture-proof gloves
when handling it and use both hands. Most
important Japanese lacquer objects were
supplied from the maker wrapped in a suitable
cloth inside a (wooden) box for protection.
This is how objects are generally stored in
Japanese museums. There are many advantages
to this system in reducing exposure to light,
handling and RH changes. However, there may
be some disadvantages that it would be wise
to consider before adopting this system.
Lacquer objects decorated with lead (or alloys
high in lead and low in tin) are susceptible to
damage by organic acid vapours from wood.
Boxing in acid free card may be an alternative
for such pieces (Umney and Winness, 1994).
A good source of practical illustration of a
wide range of the problems that may affect
lacquer objects is provided by Chase (1988).
A good bibliography of scientific research on
urushi is provided by Sano (1993). The
proceedings of the 1993 International Symposium
on the Conservation and Restoration
of Cultural Property, in which Sano’s paper is
published, are an excellent source of further
information on all aspects of the conservation
of oriental lacquer.
8.9.7 Japanning
Japanned surfaces were originally intended to
imitate oriental lacquer (urushi). The term
japanning is usually applied to designs that