Series editors' preface - Wood Tools

Figure 15.4
Reverse side of a
music stand,
English, c.1810,
before treatment.
Parafilm has been
used to protect the
varnished and
decorated paper
surface adjacent to
the metal
between the metal fitting and adjacent wood
(Figure 15.4).
Electrochemical and electrolytic
reduction
Electrochemical reduction of corrosion
products, described by Plenderleith and
Werner (1971), was often used in the past. It
relies on the corrosion of an anodic metal to
supply electrons to the cathodic metal, which
reduces the corrosion products (see section
8.4). Copper objects, for example, were
immersed in zinc, in the form of pellets,
powder or granules, and sodium hydroxide or
sulphuric acid added and heated. A similar
technique utilized strips of aluminium foil for
the treatment of silver. Such treatments may
be problematic because observation of the
progression of the reduction treatment may be
difficult and corrosion products were
sometimes redeposited on the surface. Such
products were often not originally present on
the surface and were difficult to remove.
Electrolytic reduction, which utilizes an
electric current and an electrolyte to reduce
corrosion products, has become more sophisticated
and is particularly suitable for the treatment
of lead. Electrons are given up by the
metal in the process of forming corrosion
products. Electrolytic reduction ‘reverses’ this
process by supplying electrons from a direct
current source. In electrolytic reduction, the
object is wired as a cathode in an electrolytic
solution and corrosion products are converted
back to free metal or to a lower oxidation state
(a)
(b)
(c)
Conserving other materials I 681
Figure 15.5 Electrolytic reduction
(a) The inner lock cover of a seventeenth-century
strongbox before treatment. Corrosion and previous
applications of oil and wax coatings have darkened
formerly bright surfaces. (b) Tank and treatment set up
for electrolytic cleaning of the lock cover. Corrosion on
the lock cover was reduced and removed using direct
current in an electrolytic solution of sodium carbonate
(c) Lock cover after treatment. Coatings were removed
with sodium hydroxide, corrosion removed by
electrolytic reduction and mechanical polishing