Series editors' preface - Wood Tools

e used cautiously and with suitable health
and safety precautions. A wide range of colour
effects may be achieved, from yellow to a dark
reddish brown depending on the species of
timber, so some experimentation may be
needed to achieve the desired result.
Ammonia (NH 3) is a gas at room temperature
and is soluble in both water and alcohol.
When dissolved in water it forms ammonium
hydroxide (NH 4OH) and it is in this form that
it is usually used. Ammonium hydroxide was
traditionally used to darken woods that
contain tannic acid. Tannic acid may be used
in conjunction with ammonium hydroxide or
with iron salts to form a brown stain that can
be applied to wood. Tannic acid can be
painted onto a surface as a pre-treatment,
although if this step is necessary the stain may
prove to be fugitive. Ammonia is extremely
unpleasant to use, so although brushing a
large surface is possible, it was generally more
practicable to enclose an object and expose it
to ammonia fumes. Fuming had the additional
advantage that it did not raise the grain of the
wood. A test piece may be used to check the
progress of colour change. Exposure to
ammonia fumes will corrode or discolour
many metals and other susceptible materials.
Sodium carbonate (household washing
soda, Na 2CO 3) may be used to produce an
aged effect on some woods. It is one of the
few materials that will effectively colour the
rays of oak.
Solvent borne stains Water stains used in the
past by furniture restorers, such as Vandyke or
walnut crystals, were derived from natural
materials. Most exhibited poor lightfastness
and poor resistance to acids and alkalis. In
addition they are not compatible with many
modern lacquers and these properties lead
most traditional materials to be defined as
‘poor quality’ stains. The term Vandyke brown
may refer to a pigment that is a bituminous
ferruginous earth, Cassel brown treated with
aqueous sodium carbonate or ground and
fermented walnut shells. Modern water stains
may be based on organo-metallic dyes,
complexes of chromium, cobalt or copper
with organic molecules, which vary considerably
in their lightfastness. Some manufacturer’s
water stains are not dyes but are based on
microfine pigments. Other chemical types are
Conserving transparent coatings on wood 619
also used and it may be necessary to contact
the manufacturer or supplier for technical
specifications and information about chemical
stability, lightfastness and compatibility with
coating materials.
Water stains may bead slightly on application
to bare wood. Some manufacturers
recommend the addition of a small amount of
ammonia to reduce surface tension and
increase penetration (20 ml ammonia to a litre
of water stain). The addition of a surfactant
such as Photo-Flo may be useful in promoting
even wetting of the surface. Water stains are
easy to apply and accept all types of traditional
coatings. They may be applied to bare
wood but can also be applied between sealing
coats during retouching using the method
outlined below.
Traditional water stains are prepared by
mixing about 30 g of powder in a litre of
water. Modern water stains should be mixed
according to the manufacturer’s instructions.
Brush, rag or spray application may be used,
and any excess wiped away along the grain
with a rag. A surface coating may be applied
after about 12 hours if the atmosphere in the
workshop is warm and dry. The application of
a water stain to bare wood swells the wood
fibres and raises the grain. This effect can be
minimized by pre-wetting the area to be
stained, allowing it to dry, and then abrading
the uneven surface with 180 grit paper along
the grain. Once the stain has dried, a sealing
coat can be applied and allowed to dry. The
surface can then be lightly abraded to remove
any further raised grain caused by the application
of the water stain. Subsequent coats of
surface coating will need only the usual denibbing
with 240 or 400 grit paper between coats.
As their name implies, spirit stains are
soluble in alcohol and as a result are very
quick-drying. They can be sprayed onto a
large surface but are not generally brushed
onto bare wood because overlapping strokes
produce a streaky effect. They were generally
used for tinting alcohol-soluble varnishes or
for adjusting colour during French polishing.
Spirit stains described in twentieth century
finishing manuals usually consisted of an
aniline dye dissolved in ethyl alcohol or a
similar solvent. They were notorious for their
tendency to fade, particularly the reds, and
were considered ‘fugitive’. Modern stains that