Series editors' preface - Wood Tools

acrylic paint may be used if it is diluted to the
consistency of water colours. Nagy (1998) has
considered a range of materials for filling
losses to white marble in an outdoor environment.
Coatings
The application of a coating should be considered
on a case-by-case basis. A thin coating of
microcrystalline wax may be appropriate for
polished and eroded polishable surfaces if the
furniture is in use (Figure 16.2). This will facilitate
future cleaning and act as a barrier to
spills and dirt that result from handling. A thin
layer of wax paste, diluted with solvent to the
consistency of cream, may be applied using a
brush or soft cloth and buffed to a low sheen.
As a general rule varnish type coatings are difficult
to remove from porous stone surfaces
and should not be used.
Figure 16.2 A seventeenth century Italian table top,
slate with scagliola inlay. Detail showing loss of surface
polish from the scagliola and deterioration of the slate
surface. A thin layer of microcrystalline wax can be
used to resaturate the colour
16.1.2 Scagliola
There are comparatively few sources available
on the conservation of scagliola. Zecchini
(1992) described the history and construction
of scagliola. Agnini et al. (1998) described the
restoration treatment of scagliola choir stalls in
Kempten, Germany. Wittenburg (1999) outlines
the results of a two-year research project into
Baroque artificial marble and includes bibliographic
material as well as recommendations
for conservation.
Conserving other materials II 717
Cleaning
Like marble, scagliola is a porous surface and
skilled solvent or aqueous cleaning involves
application of a small amount of liquid, which
solubilizes the dirt and is rapidly removed. If
solvent penetrates the porous surface, it will
carry any solubilized dirt deeper into the body
of the plaster, thus swabs allow controlled
cleaning.
When scagliola is in good condition and its
polished surface is intact, it may be cleaned
using the techniques described for marble,
with the exception that bristle brushes should
not be used. In contrast, broken or worn surfaces
will be very porous. In such cases cleaning
will be more problematic and cleaning
methods used for plaster may be more applicable
(see for example, Haller and Schliessl,
1998). Dry cleaning methods, described in section
11.2.4, may be effective on a stable surface
either on their own or in combination with a
swab slightly dampened with water or solvent.
Preservation pencils produce nebulized water
vapour, the flow and temperature of which can
be adjusted to allow controlled and localized
application of moisture whilst using a swab to
remove surface dirt.
Scagliola may have been treated in the past
by the application of oils or varnish. In some
cases these may be removed using solvent
poultices but such treatments may be problematic
and should be referred to a specialist.
Consolidation
One of the difficulties associated with the consolidation
of a crumbling scagliola surface is
that there is a danger of causing darkening,
tidelines and discoloration when applying a
consolidant. One way of avoiding this is to use
repeated applications of a very weak consolidant
solution, such 0.5% Paraloid B72 in a solvent
with a slow to medium evaporation rate.
Penetration of the consolidant may be assisted
by pre-wetting the surface with a solvent compatible
with the consolidant. Once applied, the
consolidant should be allowed to dry and the
surface checked for discoloration before further
application.
Cracks may be consolidated in a variety of
ways. Two or three applications, by syringe if
necessary, of 0.5% Paraloid B72 solution or a
very dilute conservation grade PVAC may be
followed by a thicker conservation grade PVAC