Series editors' preface - Wood Tools

16
Conserving other materials II
This chapter introduces the principles and
techniques for the conservation of diverse
materials often associated with wooden furniture.
Each of these materials is a specialist subject
in its own right. It is essential that
conservators undertake further research, consult
references and seek specialist advice rather
than undertaking treatments on an unfamiliar
material. The conservator should be as well
informed as possible about these materials and
be alert for potential problems in order to
avoid causing irreversible damage.
16.1 Stone and related materials
Stone is a porous material. Porosity varies
according to the type of stone and the type of
finish. A highly polished marble surface, for
example, is usually less porous than an eroded
surface. Surface coatings that may have been
applied, such as wax, will also affect the porosity
of the surface. Porosity will affect the way
dirt collects on the surface and the behaviour
of liquids applied to clean it. Capillary action
will draw liquids into the body of the stone
and there is a risk that dirt in solution may be
carried with them. Polishable stones, such as
marble, become more porous if the polished
surface becomes degraded. A furniture conservator
may undertake cleaning of a surface that
is in good condition. Problematic surfaces,
such as those that are degraded, should be
treated by a specialist.
A range of stone and stone-like materials
have been incorporated into furniture. The first
step in treatment is to identify the material/s
that are present. It may be helpful to examine
an unpolished surface, such as the underside
of a table top. Compare the top and bottom
surface but keep in mind that plaster may have
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been used as an adhesive layer. Specialist
advice should be sought if identification is difficult.
Materials such as slate, coadestone and
alabaster may be encountered, and conservation
treatment will vary accordingly. Alabaster,
for example, is readily soluble in water so irreversible
damage may occur if aqueous cleaning
solutions are used.
Much of the literature available about cleaning
and repair of stone is geared towards the
conservation of historic buildings, e.g. Ashurst
and Dimes (1990) and Winckler (1973). There
is a difference in approach between major
structural buildings conservation and that
required for stone found as a component of
furniture. Whilst much useful information may
be gained from general texts, this difference
should be borne in mind when considering
adopting the approaches or techniques outlined
in them.
Although stone is a durable material it is vulnerable
to damage from abrasive cleaning.
Proprietary metal polishes such as Autosol,
abrasive powders such as pumice, or abrasive
materials such as 0000 wire wool are not
appropriate for stone surfaces.
16.1.1 Marble
Whilst fine white marble has been prized as a
stone for statuary, marble used in furniture
tends to be highly figured, coloured and
veined. Veins may be a point of structural
weakness or more easily eroded in use.
Cleaning
The types of unwanted surface accretions
encountered on marble table tops may be
broadly characterized as a general build up of
dirt, grease or finger marks, paint marks, food
and drink stains, copper or iron stains and