Series editors' preface - Wood Tools

210 Conservation of Furniture
hardware. Unlike steel, brass cannot be
hardened (tempered) by heating but it can be
made hard and springy by cold rolling and
softened by heating.
Common white metals
Silver (Ag) has been used in furniture as an
inlay metal, in sheet and leaf form, or cast to
shape for mounts and decorative hardware.
Silver is frequently alloyed with copper to
increase its hardness and reduce its cost.
Sterling silver, an English legal standard, is
7.5% copper and 92.5% silver. Nickel silver, a
cheap imitation of silver, is an alloy of copper,
nickel and tin.
Like gold, pure silver can be beaten into
leaf. Though not as widely used as gold leaf,
silver leaf was frequently used on frames and
furniture in northern Europe in the second half
of the seventeenth century and has been in
continuous use in Mediterranean countries. It
was sometimes used to imitate gold by the
application of a yellow/brown lacquer, for
which several recipes are given in gilding
manuals (e.g. Scott-Mitchell, 1905), but often
silver was used as a decorative material in its
own right. In France after the Middle Ages it
was illegal to use silver to imitate gold and
therefore it was not used to the same extent
as in other countries. Examples of French
silvering do exist, however, and the metal was
much admired. Currently, 100% pure silver leaf
may be purchased in books of 25 leaves each
9595 mm, and four to five times the thickness
of gold leaf. Silver leaf is applied by the
same methods as gold leaf. Because it is
heavier and less ductile it is more difficult to
apply with water, though if so applied a high
burnish can be achieved.
Tin is the major constituent of pewter which
also contained copper, antimony and lead.
Pewter was used for cast hardware. In sheet
form it was often used in juxtaposition with
blue coloured horn in boulle style marquetry.
The lead content of pewter to be used with
food was regulated by law, but for other uses
lead could be present in large percentages.
Zinc was a major component of oriental
alloys imported into Europe as curiosities
before the mid-eighteenth century: the silvery
paktong (a zinc/copper/nickel alloy) from
China was occasionally recast into European
designs for furniture mounts.
Aluminium was only isolated from its ore in
1845 and was a rare metal until it was
commercially produced by electrolytic
methods after 1886. Aluminium is lightweight,
strong and corrosion-resistant in normal use
and has therefore become important as a
structural metal in furniture. In fact, aluminium
is highly reactive but the thin oxide layer that
quickly forms generally prevents further
reaction and the metal can therefore be
considered stable under normal conditions.
Gold leaf
Pure gold is completely resistant to atmospheric
attack and will retain its lustre indefinitely.
This quality, and its rarity, have given
gold social and cultural value above all other
metals. The most malleable of all metals, gold
may be beaten into leaves of extreme thinness
(0.1 m is possible) that conform to the most
intricate shapes and cover large surfaces
economically.
The traditional process of gold leaf production
is described by Scott-Mitchell (1905) and
by Wheeler and Hayward (1973). Modern leaf
is made by casting, rolling and hammering,
which leaves a poorly ordered pattern of plates
with extensive distortion of the basic atomic
arrangement with holes and tears and very little
mechanical strength (Lins, 1991). The starting
point for the production of leaf is gold of up
to 99.95% purity alloyed with other metals in
varying proportions to produce leaf of different
colours. Traditionally copper and silver were
used but platinum and palladium have also
been used more recently. Copper gives gold a
warm tone, copper and silver together give
mid-range tones, and silver produces cool tones
(see Table 5.2). Leaf alloys of less than 50%
gold by weight are rare. The carat system of
measuring gold content refers to a 24th part.
Thus 18 carat (ct) gold contains 18 parts of gold
and 6 parts of alloying metals. The gold leaf
most commonly used now is 22 or 23 carat.
Depending on the country and period of origin,
several colours of gold may be found on a
single object. Furniture and picture frames have
also been gilded with leaves of Dutch metal (an
alloy of copper and zinc), silver leaf, or even
leaves of two different metals beaten together,
known as schlagmetal.
Gold leaf is sold loose in books of 25 leaves
laid between rouged tissue. A ‘pack’ consists