Series editors' preface - Wood Tools

344 Conservation of Furniture
use a contrast between a monochrome
background (black, red, green, blue etc.) and
decorative designs, often picked out in gold,
that have an ‘oriental’ influence or feel
(chinoiserie). Japanning describes the decorative
effect rather than the materials used and
thus the term spans several centuries and
encompasses surfaces based on alcohol
soluble (‘spirit’) resins, oil paint, oil soluble
fossilized resins and stoved linseed oil.
Treatises describing the techniques used in
japanning furniture in seventeenth and early
eighteenth century England provide a comprehensive
picture of a complex laminate structure
which may include priming, up to
twenty-four layers of varnish which may be
decorated with pigments, metal and raised
detail which are in turn secured to the body
of the work with up to ten further coats
of varnish (see section 4.4.7). The materials
are not as durable as those used for the preparation
of oriental lacquer and the layered
structure is composed of materials whose
properties are not always compatible. Most of
the problems outlined within this section (8.9)
are well represented in japanned objects.
Delamination and loss of the japanned
surface through moisture induced movement of
the wooden support is a common problem
though some woods are noticeably worse than
others. Japanning does not survive as well on
beech or oak, where it is often found to split,
crack and flake off, as it does on pear, walnut
or lime, for example. The use of veneer may
also prove problematic because adhesive failure
leads to lifting which results in cracking of the
surface decoration and loss of raised work.
Gum lac and many other natural resins have
a tendency to yellow, darken and become
insoluble (more polar) with age. Some resins,
such as sandarac, are very brittle and films
containing them become more so with age and
tend to crack in service. Oleoresins, added to
varnish films to increase their elasticity, also
tend to become rather brittle once dry. Despite
the attempt by japanners to balance the
properties of the ingredients in their varnish
formulations to achieve a result that would be
as transparent and long-lasting as possible,
varnishes do discolour and therefore alter the
appearance of the pigment underneath. The
collagen-based isinglass medium that was
adopted for the production of blue and white
grounds in recognition of this problem was
itself apt to ‘crack and fly off’ if used too
strong. If used too weak it is liable to adhesive
failure. Some materials, particularly shellac (as
opposed to seed lac), may have been adulterated
or otherwise impaired in performance by
the refinement process. Carbon blacks are very
poor driers in oil paint due to the large amount
of oil they absorb. A film of any other pigment
laid over them is therefore very likely to crack
as a result. Verdigris, a reactive and unstable
pigment, was sometimes added to improve the
drying quality of oils containing carbon black.
Shellac films are sensitive to moisture and may
bloom in high RH and on contact with liquid
water. The use of spirit-based varnishes in
japanning renders the entire finish vulnerable
to damage from alcohol and moisture. The
combined use of spirit soluble resins as
medium and as varnish makes this type of
decoration particularly difficult to clean and
treat since the decoration is essentially locked
up in the varnish. It is also very easily
damaged during removal of layers of varnish
applied in old restoration treatments.
The base colour was decorated after it had
been varnished and rubbed down with an
abrasive lubricated with oil. Despite subsequent
efforts to degrease the surface it is
probable that small amounts of oil would
sometimes remain to impair the adhesion of
applied raised decoration. Both silver and the
base metals used to decorate surfaces are
subject to tarnish by sulphur-containing gases
present in the atmosphere and by the acidic
nature of resins used as media and varnishes.
Weak gum arabic water, recommended for
attaching painted decoration, has been a factor
in the deterioration of both pigment and metal
powder decoration. Raised detail is especially
vulnerable to damage and loss as a result of
both wear and tear and adhesive failure
caused by differential expansion between the
detail and the substrate.
Nineteenth century oil-based japanning may
be prone to delamination, particularly from
papier mâché substrates.
Japanned objects are frequently found to
have been overpainted, revarnished and
restored. Examples of deteriorated japanned
surfaces are illustrated in case studies by
Ballardie (1994), Beale (1994) and Wachowiak
and Williams (1994).