Series editors' preface - Wood Tools

212 Conservation of Furniture
achieved by the application of gold–mercury
alloys (amalgam). The silver coloured buttery
amalgam was applied with a stiff wire brush
to presentation surfaces. The object was then
heated to vaporize the mercury leaving a dull
coating of gold that was burnished to a high
shine. Ormolu furniture mounts are predominantly
brass alloys fire gilded using this highly
toxic and dangerous mercury process.
Organic coatings have also been extensively
employed on metals. Waxes and oils work
well on unpolished or rough work, while spirit
varnishes based on shellac or sandarac were
commonly used on polished work during the
eighteenth century and later. Lacquers for
white metals were often coloured with dyes or
with the alcohol-soluble coloured resins
gamboge and dragon’s blood to imitate the
colour of gold. Since the age of modern
plastics, a host of synthetic resins have been
used as clear coatings and paint binders on
metalwork. Intentional chemical patination of
metals has been widely used for decorative
effect (Hughes and Rowe, 1982).
For further information on the history and
technology of metals see Singer et al. (1954–
1958) and Street and Alexander (1979).
Identification of metals
Some metals and alloys have a characteristic
colour, specific gravity or corrosion product
that can be used to make a preliminary identification
of the material. However, when
making a visual identification it should be
considered that the presence of coatings,
patinas, corrosion and dirt can affect the
appearance of metal.
Qualitative microchemical tests, based on
the formation of characteristic colours or
precipitates on reaction with a specific test
reagent, can be used for the identification of
metals and alloys (Laver, 1978). The lower
limit of detectability of an alloying element is
generally between 0.2 and 1.0% (Newell,
1982). The tests are carried out either as spot
tests on the metal surface or involve sampling
(Laver, 1978). A disadvantage of this destructive
method is that the presence of each
element has to be detected individually.
Thomson (1991) suggests a battery continuity
tester to detect the presence of non-conductive
organic coating or corrosion layers on a
metal surface. The ferromagnetism of iron and
nickel makes it possible to identify them with
a magnet.
Various instrumental analytical methods,
including X-ray fluorescence (XRF), energy
dispersive X-ray spectrometry (EDS), atomic
absorption spectroscopy (AA), neutron activation
(NA), emission spectroscopy (ES), proton
induced X-ray/gamma-ray emission (PIXE/
PIGE) and photon activation may be used to
identify metals and alloys (Parkes, 1987).
These analytical methods, as well as X-ray
diffraction and infrared absorption spectroscopy,
may also be useful in the characterization
of corrosion products.
Identification of structure and
fabrication of metal objects
General methods of manufacture, e.g. casting,
pressing, turning or assembling, can be recognized
from the overall appearance or shape of
the metal component. Visual examination,
especially in raking light, may reveal features
of the manufacture and decoration techniques
such as mould marks from casting, incised
grooves from engraving or compressed
channels from chasing (Larsen, 1993; Watts,
1982). Silicon rubber casts, which provide a
reversed relief of the surface, can be an aid in
the study of tool marks. The regularity of the
tool marks may indicate whether or not the
metal was worked by hand or machine, e.g.
hammering versus rolling or, as in the case of
screws, hand filing versus machine threading.
The identity of the maker, workshop or origin
may be recognized through stamped marks
(Brandner, 1976; Kisluk-Grosheide, 1991;
Stratmann, 1975) or inscribed signatures (Van
Duin, 1989). Visual examination may also
reveal whether or not the applied hardware is
original to the furniture, as the presence of
outlines, marks, holes and plugs can indicate
previous attachments. A hand lens and stereomicroscope
may reveal further surface details
such as concentric scratches from turning or
the cut edge characteristic of a fretsaw blade.
Metallographic examinations reveal the
internal grain structure of metals, thus providing
information on the techniques employed
in their fabrication. A polished and etched
cross-section is prepared from a sample
removed from the object and examined in
reflected light using a metallographic microscope
(Scott, 1991). Elemental analysis of