Series editors' preface - Wood Tools

Figure 15.11 A gold snuff box, c.1814. Disfiguring
tarnish caused by the corrosion of metals alloyed with
the gold
(a)
(b)
Figure 15.12 Eighteenth century statue of Tara, Nepal
(a) Detail of foot before removal of corrosion products.
The metal is a gilded copper alloy. Corrosion products
from the copper obscure the gilt surface
(b) Detail of foot of statue, after cleaning. The gilded
surface was revealed by the removal of copper
corrosion products. This is the type of alloy that might
have been cleaned with ammonia in the past but is
now more safely cleaned using chelating agents,
followed by rinses of deionized water and acetone
Conserving other materials I 697
corrosion products can emerge from the pores
and spread over the surface of the gold
(Figure 15.12a). This may also occur where
the gold layer is not continuous, for example
if it has been worn away.
Electroplating will result in an even layer of
gold over the whole mount, whilst mercury
gilding was applied only to the presentation
surface. Gilding has often been imitated and
reproductions, particularly neo-classical objects
and designs, were cast in zinc alloys (e.g.
spelter) or Britannia metal. Such pieces cannot
be cleaned using the materials set out below.
Cleaning
All gilding layers tend to be fairly thin and are
vulnerable to wear. Dirt may be removed with
hydrocarbon solvents. This treatment is often
sufficient if the surface is not corroded.
Ormolu was often left partly matte as a
decorative contrast to adjacent burnished
areas. Care must be taken to avoid burnishing
the surface – it may be possible, for example,
to burnish the gold using cotton wool and
heavy pressure. Non-original varnish or
splashes as a result of finish applied to
adjacent wood can usually be removed using
organic solvents.
In some cases mounts were not gilded at
all. In the early eighteenth century brass
mounts were often polished or acid dipped
and then lacquered, a technique known as
mise en couleur de l’or (Tear, 1996). In many
cases a colouring agent, such as crushed
liquorice, turmeric or saffron, was added to
the lacquer.
Removal of corrosion products
When considering chemical treatment for
removing corrosion products it should be
borne in mind that the overall appearance of
the object should be consistent, for example
the balance between cleaned mounts and
inlaid brass, or mounts and faded wood.
Removing corrosion products without
damaging the gold layer may be problematic.
Mechanical removal of corrosion products will
result in damage to the gold and mechanical
removal of corrosion products is usually
limited to brushing over the surface with a
very soft brush. In some cases it may be possible
to pick corrosion products from the
surface with the point of a scalpel.