Series editors' preface - Wood Tools

emoval. Dusting or wiping over the surface
will remove loose material. The presence or
absence of original paint, lacquer or more
recent coatings should be established before
undertaking solvent cleaning. If such coatings
are not present, the surface may be degreased
using white spirit or industrial methylated
spirits (IMS). As a general rule, immersion in
water should be avoided unless followed by a
thorough rinsing and drying procedure (see
section 15.3.4).
Coatings are often applied to metal in an
attempt to prevent or slow corrosion. Two
common types of coating that have been
applied to the metal components of furniture
include paint and varnish, called lacquer when
applied to metal. In many cases metal components
have been varnished with the same
materials used to finish adjacent woodwork. In
some cases, however, coatings were applied
which incorporated dyes or other materials
that were specifically intended to enhance the
appearance of metal components on furniture
metal (Thomson, 1991). Before a conservation
treatment is undertaken, the presence of such
lacquer, which it may be desirable to
conserve, should be identified. Indications of
the presence of such coatings include the
absence of tarnish or corrosion on a metal that
would normally be expected to tarnish. The
presence of areas of metal that are well
preserved but adjacent to areas with a
degraded or corroded surface, such as tarnish
on the high areas and bright metal in the low
areas, may indicate a lacquer that has begun
to degrade. The presence of original patination
may be indicated by the presence of a
high polish or an even colour that differs from
the natural appearance of the polished metal,
which may itself be visible if the surface has
been scratched.
15.3.3 Removal of corrosion products
Removal of corrosion products always involves
the removal of what was once material original
to the object. Some loss is inevitable,
whether mechanical or chemical methods are
used. The removal of corrosion from metals
requires the conservator and/or curator or
owner to make an informed decision that
balances the degree of corrosion product
removal against the potential for, or degree of
Conserving other materials I 679
Figure 15.3 Filiform corrosion on a seventeenth
century strongbox. Filiform corrosion occurs under
coatings and has a threadlike appearance. It is caused
by poor surface preparation of the metal before a
coating is applied in combination with elevated RH
(c.80%) once the coating has dried. The corrosion
mechanism is similar to pitting corrosion
acceptable, damage. Repeated use of abrasive
or chemical polishes, for example, may
eventually lead to the loss of decorative detail,
plating, chasing, filigree work or hallmarks.
The successful removal of corrosion from
metal requires skill and experience. There are
subtle differences in metal alloys and corrosion
products. A chemical or process applied
by an experienced conservator may be
successful whilst inexperience may cause
irreparable damage. Given the damage that
may be caused by repeated corrosion removal
treatments, consideration must be given to
storage or display conditions so that further
corrosion and future treatment is minimized
(Figure 15.3). RH should be minimized as far
as is practicable within the context of the
object as a whole, and gloves should be worn
when handling metal to protect it from salts
and oils present on skin which, if left on the
surface of metal, will permanently etch it.
Coatings may not be sufficient to protect the
metal from volatile organic acids or residues
left by ungloved handling.
There are three methods of treating accretions
of corrosion products on metal objects –
mechanical removal, electrolytic and electrochemical
reduction, and the use of chemical
reagents to remove corrosion products or
stabilize the metal against further attack. The
first and last are most commonly used in furniture
conservation. All may be used over the