Series editors' preface - Wood Tools

646 Conservation of Furniture
considered the best brushes to use for applying
clay, although ox hair or even nylon are
cheaper and can work well. Round brushes
are ideal as they hold and distribute the clay
evenly. Flat or round sable brushes may also
be used for applying a coating to the gold.
Sable-ox hair mixtures for larger sizes offer
some economy over pure sable whilst retaining
good working properties. Separate brushes
should be used for water gilding and oil
gilding, as oil residues will prevent adhesion
of water gilt leaf.
14.1.3 Gold and metal leaf
Modern gold leaf is slightly thinner than that
used by the Egyptians or in medieval Europe.
Gold leaf is prepared by casting bars that are
then rolled and annealed. The leaf was hand
beaten to its final thickness. Gold leaf has been
machine beaten to its final thickness since the
late nineteenth century, though traditional
hand beaten gold leaf is still manufactured on
a small scale. Commercial twenty-four carat
gold leaf may vary between 0.3 and 0.8 μm.
Pure gold leaf is available in ‘single’ and
‘double’ weight. There is no industry standard
for the thickness of gold leaf and as a result
the thickness of one manufacturer’s leaf may
be nearly double that of another, but both may
still be named ‘regular’. Gold leaf is available
as loose leaf and transfer leaf. Loose leaf may
be used in water or oil gilding and is applied
with a gilder’s tip, whereas transfer leaf, also
available in rolls, is pressed onto a mordanted
or oil sized surface and cannot be burnished
to a high lustre. Other metals such as copper
or silver may be alloyed with the gold to
produce leaves of differing colour and
hardness (Plate 7 and see Table 5.2). The
presence of alloy metals may cause gold leaf
to oxidize and change colour over time, particularly
in lower carat weight leafs where the
non-gold content is higher. Other types of
metal leaf include silver, white gold, copper,
aluminium, palladium and platinum. Silver,
platinum and palladium leaf are slightly thicker
than gold leaf. Schlag leaf, also known as
Dutch metal, is a thick leaf alloyed from
copper and zinc with a marked tendency to
tarnish if it is left uncoated. Aluminium, copper
and schlag, used only in oil gilding, require
slightly different handling techniques, which
are outlined by MacTaggart and MacTaggart
(1984). Lewis (1763–5) describes the process
used to manufacture gold leaf in the eighteenth
century whilst MacTaggart and MacTaggart
(1984) outline the modern process.
Any excess pieces of gold that are too small
to be used on the piece, or are brushed from
the surface after gilding is complete, are called
skewings. They may be collected separately
according to the colour of the leaf and used
to make gold powder, which is expensive and
may be difficult to obtain from commercial
suppliers. When a sufficient quantity of
skewings have been collected they are mixed
with a small amount of honey and ground into
a powder using a mortar and pestle or a slab
and muller (Cennini, trans. Thompson, 1954).
Although the process should take only 10 or
15 minutes, the longer the skewings are
ground, the finer the resulting gold powder
will be. Very fine powder will appear slightly
dull whereas very large particles will tend to
clump together in use. The gold powder may
be separated from the honey by placing the
honey and gold mixture into a container and
covering it with hot water. When the gold has
settled to the bottom the water may be poured
off. This process may be repeated five times,
the last two rinses with deionized water. If
making powdered gold, most of the last rinse
water may be poured away and the remainder
left to evaporate. The powder may be
made into a gold paint, also known as shell
gold, by the addition of a drop of concentrated
gum arabic when most of the water has
evaporated (MacTaggart and MacTaggart,
1984). Shell gold and powdered gold are
painted on with a brush or rubbed onto the
surface with a finger. Shell gold, in gum
arabic, requires only the humidity of a breath
to reactivate the medium, whilst powdered
gold requires the application of a layer of size
or mordant. Shell and powdered gold are
mostly used for letter-writing, drawing small
designs, repairs to small abrasions or may be
used in deeply carved recesses that would be
inaccessible to gold leaf.
14.1.4 Surface preparation
A surface that is to be gilded should be clean,
stable and free from defects. In the case of
water gilding on wood, it is critical that the