Series editors' preface - Wood Tools

678 Conservation of Furniture
technical evidence. Information on the conservation
of metals may be found in conservation
literature that deals with the treatment of archaeological
and historical metal objects, although
articles on the conservation of industrial collections
and modern metal artefacts may also be
useful. Related disciplines such as the conservation
of scientific instruments and horology may
also provide helpful references. Publications that
may prove useful include MacLeod et al. (1995),
Mourey and Robbiola (1998), Scott et al. (1994)
and Slater and Tennent (1979). Spot tests for the
identification of metals are described Ganiaris
(1985) and Townsend (1985, 1988).
Ethical issues have generated significant
debate in the discipline of metal conservation.
An issue specific to metal conservation is the
effect of repairs that utilize heat treatments.
Hot metal joins such as soldering, welding or
brazing alter metallographic structure, will
change metal colour and patination and may
interfere with future analysis. Repairs utilizing
heat may affect function, for example springs
that are heated may no longer function as
springs. If welding is necessary, TIG or MIG
welding are the best alternatives because
fluxes are not necessary and the heat is
intense, brief and localized, minimizing
conduction and metallographic alteration.
The treatment of metal fittings on furniture,
or metal furniture itself, must be considered
within the broader context of furniture conservation.
Bending metal back to its original
shape changes the metallographic structure. In
the context of furniture, the retention of original,
functional fittings is usually ascribed a
higher priority than unchanged metallographic
structure.
Patina
Some corrosion layers are considered attractive
or may attest to the passage of time and are
therefore considered to be of value whilst
others, such as the tarnishing of silver, may
not. The term ‘patina’ is often used as a value
judgement for any corrosion product that is
considered to enhance the appearance and
value of an object. Metal conservators generally
use the term to denote an artist- or
manufacturer-applied corrosion product that
was part of the original intent.
Perceptions of appropriate appearance are
influenced by culture and fashion. The owner
or curator’s opinion should be sought before
undertaking treatments that may radically alter
the appearance of metal. Consideration should
be given to the overall aesthetic balance of the
object. Furniture decorated with marquetry
and metal may appear unbalanced, for
example, if the metal is highly polished whilst
the colour contrast of the wood has faded to
a mellow interplay of shades of brown.
Metals and their surface finishes, including
ferrous metals, are softer and more porous
than is often imagined. Decorative layers, such
as gold or silver, are not only soft but may
have been applied in very thin layers and are
very easily damaged. In some cases, including
gilding, ormolu and other surfaces, finishes
were deliberately left with a ‘frosted’ or matte
finish, patinated or painted. It should not be
automatically assumed that the original finish
was brightly polished, and buffing or polishing
surfaces is often inappropriate. The
blanket treatment of metal fittings on furniture
with abrasives is not acceptable because metal
treated in this way will not reflect the age or
use of the object.
Wood in contact with hardware, for
example iron hinges, screws or nails, is often
discoloured. High moisture content as a result
of elevated RH may cause leaching of iron
ions and produce a blue/black (iron tannate)
discoloration in oak and other woods with
high tannic acid content (Panshin and de
Zeeuw, 1980). Such discoloration is often
considered to be evidence of age.
Removal of metal fittings
The removal of original hardware and fittings
should be avoided wherever possible. Items of
hardware, such as screws or handles, that are
removed to allow conservation should be
labelled and stored so that they can be
returned to their original position. Soft white
foam may be used for this purpose, or a tag
of masking tape that notes the original
position may be attached to the thread.
Techniques for the removal of screws are
discussed in section 10.2.1.
15.3.2 Cleaning
As a general rule, accretions of dirt or grease
are removed before dealing with active corrosion
so they do not interfere with tarnish