Series editors' preface - Wood Tools

Boucher (1995) described a technique that
utilized cold set liquid animal/hide glue to
consolidate marquetry in situ. Thin gauze or a
similar fabric is dampened and placed over the
surface until design elements begin to lift. The
cloth and water are removed and a cold set
animal/hide glue brushed onto the surface and
worked under damaged or lifting veneer. A
thin layer of plastic is placed over this gluey
surface and the whole transferred to a press
that has been pre-heated to 65 °C. The heat is
turned off after five minutes and the marquetry
left under pressure until the glue has dried (up
to a week), after which excess adhesive on the
surface is removed. This technique may be
used for boulle but loose brass should be
reglued with fish glue before treatment
commences.
Fish glue is the traditional adhesive used for
boullework, although it may be difficult to
achieve a strong and lasting bond between
wood and metal. The addition of garlic juice
was reputed to improve adhesive properties
and longevity, though it is not favoured by
most conservators. Nagora et al. (1990)
suggested the use of sturgeon glue with the
addition of 5% glycerine, whilst Triboulot
(1999b) suggested that the addition of 25% v/v
alcohol and 25 g/l dextrin to collagen adhesives
will increase the adhesion between the
substrate wood and brass. Restoration books
often recommend the use of irreversible adhesives
such as epoxy, particularly if animal/hide
or fish glue fails to stick metal down. This
problem is caused by a contaminated surface
rather than the use of a protein adhesive per se.
Epoxies are sensitive to surface contaminants
and though they may initially adhere well the
service life of the adhesive bond may be
greatly reduced if the bonded surfaces are
contaminated by dirt or grease. Many epoxy
hardeners contain amines, which can cause
corrosion of copper alloys. Problems of future
reversibility also weigh against the use of such
adhesives.
The surface of the metal that is to be
adhered must be clean and may be scored or
sanded to provide a key. The metal should be
cleaned immediately before adhesive is applied
and care should be taken not to contaminate
the surface by handling it. Some texts recommend
the use of hot cauls to lay boulle, stating
that if spit bounces straight off the metal of
Principles of conserving and repairing wooden furniture 475
the caul it is too hot but if it sits and sizzles the
temperature is right (Hawkins, 1986). Given
the stress that will be placed on the adhesive
bond as the metal cools and contracts, and the
likelihood of destroying any surface finish on
adjacent areas, such high temperatures are not
recommended for conservation work. More
recent sources have recommended temperatures
in the range of 65–75 °C.
It may be possible to introduce fresh
animal/hide or fish glue under loose areas
before cramping them down. If a natural resin
varnish is present, it may be necessary to
remove excess adhesive by applying pressure
and releasing it several times to prevent any
excess from drying on the surface and damaging
the surface finish. Often the metal surface
is contaminated and it may be difficult to
adhere. It may be necessary to lift a section of
metal and clean the back before relaying it.
Removal of old adhesive, especially from the
ground, may result in differences in the level
of treated and untreated areas. If only a small
area has been treated, it may be necessary to
apply a backing (e.g. a non-laminated paper)
to compensate for the loss of thickness in the
adhesive layer. A traditional treatment for
laying metal in boullework was to place a flake
of shellac underneath the loose end and apply
heat. If metal has been treated in this way in
the past it will require cleaning before it can be
relaid. Repeating treatment with shellac will
probably result in a repeated adhesive failure
in the future.
If decorative elements are lifted, old glue
and other contaminants must be removed
before they are relaid. Turtleshell may become
embrittled with age and it may be necessary to
soften old glue with water or a Laponite gel to
prevent fracturing of the edges of adjacent
turtleshell when the glue is removed. Bubbles
in turtleshell are particularly common in the
thin shell used on nineteenth century pieces.
Fresh glue may be worked under the bubble
and then cramped up. In some cases a combination
of water and methylated spirits (3:1)
may be sufficient to reactivate the original glue
if it is not severely degraded. In some cases the
paper used under the turtleshell has delaminated
and may be consolidated with isinglass.
Creased or buckled metal, that is not workhardened
or embrittled, may be straightened
by careful hammering, or by putting it between