Series editors' preface - Wood Tools

718 Conservation of Furniture
adhesive. Gentle cramping pressure may be
applied to bring the edges of the crack into
contact but potential weakness in the structure
of the scagliola should be considered. The
edges and surface of the object should be protected
if cramps are used.
Chips may be readhered using a conservation
grade PVAC. The chipped surfaces should be
clean and pre-sealed with a weak solution of
consolidant as described above. Repair of major
breaks should be referred to a specialist.
Fills
Areas that are to be filled should be cleaned
and coated with an isolating layer. Proprietary
products such as interior Polyfilla may be used.
A more accurate colour match may be produced
by mixing dry pigment powder with the
Polyfilla powder. Water is added once a satisfactory
colour has been achieved. Pigments
used to make scagliola were selected for lightfastness
and compatibility with lime, and as a
result natural earths and mineral colours were
commonly used. Fills may also be made using
whiting and pigment and may include aggregate
material such as ground alabaster powder
and an adhesive such as rabbit skin glue,
PVAC, or other materials discussed in section
12.3.1. Colour matching is most effective when
the fill itself matches the adjacent scagliola but
water colours, pigment in Paraloid etc., may be
used to match a marbled effect. Surface polish
may be simulated by burnishing with a fine
polishing cloth, an agate stone, or by repeat
applications of microcrystalline wax, buffing
between each layer, or a combination of these
methods.
Coatings
A scagliola surface that is clean and has
retained its original polish may be given a thin
coat of microcrystalline wax. The wax should
be buffed to a low sheen using a soft cloth. As
a general rule varnish type coatings are difficult
to remove from porous surfaces such as
scagliola and should not be used.
16.1.3 Piètre dure
The history, materials and techniques used to
create piètre dure surfaces have been
described by Giusti (1992). There are two main
methods of constructing pietre dure decora-
tion. One method is known as intarsia and,
using a technique similar to wood intarsia, the
pre-cut pieces of coloured stone are laid into a
recessed stone ground, usually marble, which
forms part of the design. The other method,
known as mosaic or commesso, similar to marquetry
used for wood, is to assemble the
pieces of the design and adhere them to a
stone support. In both cases the pieces are
adhered in place with cement or a wax–resin
(usually beeswax and colophony) mixture.
Cleaning
The condition of the structure will define the
parameters of the cleaning procedure. If the
structure is in good condition and the decorative
stone is sound and well adhered, then the
materials and techniques described for cleaning
marble may be used. Before cleaning, the
surface should be checked for evidence of
replacements or fills as this may affect the
choices for cleaning. Losses or loose pieces
should be treated before the surface is cleaned
to prevent penetration of cleaning solutions
into the adhesive and substrate.
Loose decorative elements may be reattached
using a variety of materials depending
on the nature and condition of the existing
adhesive. If the element is loose but not separate,
a consolidant such as Paraloid B72 may be
injected underneath to avoid the risk of breakage
when trying to lift and relay pieces. A traditional
method was to run a melted wax–resin
mixture between the pieces. Separated pieces
may be readhered using these materials or a
two part knife grade polyester, which is usually
available in black, white or straw colour. A
two part acrylic, such as Akemi ® , which is
available in both liquid and knife grades, may
also be used.
Fills/losses
Losses may be filled with the materials
described above and these may be tinted with
pigment as required. Some epoxies, such as
HXTAL NYL-1, may provide a higher gloss to
the surface of the fill than the materials
described above but will require the use of an
isolating layer.
Coatings
The principles and materials outlined above for
marble may also be applied to piètre dure.