Series editors' preface - Wood Tools

620 Conservation of Furniture
are soluble in alcohols, ketones and esters
include the organo-metallic Orosol dyes
(Ciba–Geigy). The best of these dyes exhibit
exceptional lightfastness, with 500 hours
exposure to carbon arc lighting before a
discernible change in colour, but some have
poor lightfastness, with change occurring after
a mere 10 hours exposure. Brown 2RL, for
example, is rated at 250 hours, equivalent to
blue wool light fastness 5–6 (Horie, 1992).
Orosol and similar dyes are a single pure
colour rather than a blend. This means that as
they age they may fade in intensity but will
not drift in hue. A proprietary product range
containing these dyes is available from J.W.
Bollom (USA).
Spirit soluble stains may be very useful in
colour matching. Some conservators simply
add a very small amount of powder directly
to the binder on a retouching palette, dissolving
and mixing it thereon. Spirit stains may
also be pre-mixed in a strongly coloured
5–10% w/v solution in pure solvent. This may
be added to the retouch binder to provide
control over the colour and intensity of a
transparent coloured wash. Pre-mixed stain
may also be added drop by drop to a French
polishing rubber when it is charged. The stain
is then carried through slowly and will subtly
adjust the colour of the finish. Applying the
stain directly to the face of the pad will
produce a streaky result.
Oil and naptha stains were traditionally
derived from bituminous sources. Oil and
naptha stains penetrate wood evenly and well
and produce rich colours, especially in the
brown shades, but can be slow to dry. The
basic material was tinted with oil soluble dyes
to produce different coloured stains, but these
all tended to fade back to the reddish brown
colour of the bitumen. With the exception of
some yellows and browns, many modern oil
stains share this poor lightfastness. Organometallic
complexes are utilized by some
manufacturers for white spirit soluble stains
and these may exhibit improved lightfastness.
Non-grain raising (NGR) stains are often
produced using a water-soluble acid dye in a
glycol ether solvent, which does not raise the
grain of the wood and promotes rapid drying.
These materials were developed for industrial
use so it is not surprising that the best results
are achieved by spray application.
Considerable skill is needed to achieve a
translucent even colour using hand application
methods such as a rag or brush. NGR stains
that contain glycol ethers require the use of
health and safety precautions. Mixed solvent
stains may also be known as NGR stains. They
are formulated from lightfast dyestuffs in
alcohol and naptha. They are fast-drying but
their wide solubility parameters mean they
may be disturbed by, or bleed into, subsequent
coats of sealer or varnish.
13.5.4 Grain fillers
Grain fillers are used to produce a full grain
finish on open grain timbers and to speed the
finishing process (Figure 13.6). Grain filling is
generally undertaken after any initial staining
process that may have been used, as the
binder in the filler could otherwise prevent
even take up of the stain. The binder for the
filler usually has different solubility to both
any stain applied before filling and the coating
to be applied afterwards. Hayward (1988),
Bennett (1990) and Flexner (1994) discuss
filling materials and techniques.
Sheraton refers to the use of brick dust and
oil for the finishing of ‘plain cabinet work’.
Other materials have been used as fillers, with
varying success. Pigmented wax may be used
as a filler for small repairs, although it may
interfere with the adhesion of subsequent
coatings. Fillers generally consist of three main
ingredients – powder, binder and solvent
carrier. Other ingredients were added as
necessary, such as driers to home made
linseed oil pastes. The fine abrasive effect of
some powders also smoothed the surface
wood fibres. Powders have included pumice,
pigments, plaster of Paris and chalk. The
binder was often oil or oil-based, including
boiled linseed oil, but could also be gold size,
hide or rabbit skin glue. The solvent carrier
was dependent on the binder – turpentine for
oil-based fillers, water for glue size. The grain
of furniture made or veneered in light
coloured woods was often filled by brush
coating and abrading varnish or in the bodying
up stage of applying a French polish. With the
passing of time, some of these materials have
proved more successful than others. Plaster of
Paris, for example, is often responsible for the
unsightly white deposit found in the grain of