Series editors' preface - Wood Tools

146 Conservation of Furniture
layer of paint to another. Sealers may also be
used to improve adhesion between layers
where this would otherwise be weak. Suitable
paint media may be used in thin layers with little
(transparent) pigment to make glaze layers
which permit subtle colour variations to be
achieved.
A wide range of substances and mixtures of
substances is found in historic paint media
used in the ‘polychromy’ or coloured decoration
of furniture. Among these are animal glue
(distemper), egg tempera, casein tempera, wax
emulsions, wax resin mixtures (encaustic) and
various drying oils and oil–resin mixtures.
Water colours are also frequently encountered
in retouches. Watin’s L’Art du Peintre, Doreur,
Vernisseur, first published in 1755, gives an
excellent account of artist’s materials and their
application. The pigments he recommended
include lead and chalk whites, red and yellow
ochres derived from clays, lapis and Prussian
blues and lamp and ivory blacks to name only
a few. He cites binders made of animal glues,
egg white, oils, such as linseed, walnut and
olive, resins such as mastic, copal and sandarac,
and gums. These materials are discussed
in more detail at the end of this chapter. A
French paint system that Watin called Chipolin
(from the Italian for garlic), consisted of parchment
glue to which garlic has been added and
whiting (ground) followed by two coats of a
glue-based paint, and then by two coats of
weak glue size. Finally, three coats of spirit varnish
were applied (Watin, 1728). The garlic
may have served to promote adhesion and
acted as a fungicide.
Fascinating and valuable historical reference
is also provided by the period treatises of
Pacheco (1649) and Stalker and Parker (1688).
Massey (1967) gives over 200 formulas for
making paints, glazes, mediums and varnishes
for a variety of painting techniques including
tempera, oil, acrylic, gouache and encaustic
with instruction on their purpose, manufacture
and use. Knowledge and awareness of traditional
paints has led to the formation of organizations
such as the Traditional Paint Forum in
the United Kingdom which focuses on the
materials and techniques utilized for architectural
paint schemes and associated furniture.
The materials and techniques of medieval
painting are discussed by Thompson (1956)
and by Hulbert (1987). Mayer (1981) provides
the artist with a comprehensive review of all
aspects of the materials and techniques of
painting. A good introduction to paint chemistry
and the principles of paint technology is
provided by Bentley (1998).
4.4.4 Transparent coatings
Transparent coatings used over painted wood
include varnishes and waxes. Oils may be
added to the list of transparent coating materials
used to finish unpainted wood. Varnishes
are transparent or translucent top coatings that
give a gloss (Perry, 1804). They are similar to
glazes but generally unpigmented and are used
to protect the finished work against moisture,
pollutant gases, dust and handling. Transparent
finishes increase the sheen and deepen the
colour of the surface by filling pits and surface
irregularities thus reflecting more light back to
the eye rather than scattering it, that is they
provide optical saturation. Historically varnishes
were based on natural resins but waxes
and oils have also been used in combination
with them in various varnish formulations, as
well as on their own, to enhance both bare
wood and finished surfaces. The twentieth century
has seen a large range of synthetic thermoplastic
and thermosetting polymer materials
added to the list of transparent surface coatings
available for wood. For a review of traditional
and modern coatings commonly found on furniture
see Mills and White (1987). For coatings
commonly used for conservation purposes, see
Horie (1987). The chemistry of these materials
is further discussed by Ash and Ash (1982),
Kolesky (1995) and Bentley (1998).
To form a continuous thin film, coatings, like
adhesives, need to be in liquid form at some
stage in their application. This requirement can
be met in various ways. Thermoplastic finishes
found on furniture are relatively hard at room
temperature but during their application heat
can be used to make them soft or fluid.
Materials such as waxes, wax-resin mixtures
and shellac can be made sufficiently fluid by
the vigorous motion of a hand-held rubbing
tool (friction polishing) or by the motion of a
lathe.
A category of thermoplastic materials,
important to coating and adhesive technology
but of minor use in plastics manufacturing, is
materials that dissolve in solvent and harden