Series editors' preface - Wood Tools

Deoxycholate soap recipe
2 g deoxycholic acid (free acid)
5–6 ml triethanolamine (TEA)
HCl (1M) to adjust pH to 8.5, as
needed
0.1 g Triton XL-80N
2 g hydroxypropyl methyl cellulose
(HPMC)
100 ml distilled or deionized water
The deoxycholic acid is added to the water and
the TEA is stirred in to form triethanolamine
deoxycholate. Hydrochloric acid is used to
reduce the pH to 8.5. The solution is filtered
and the HPMC added to gel the solution. An
additional detergent such as Triton XL-80N can
be added if required.
Resin and bile soaps require a three-stage
rinse procedure. An initial rinse with a buffered
solution of 0.5% to 1% ammonium acetate of
the same pH as the original cleaning solution
has been recommended. The buffer can be
made from a 0.5% to 1% ammonia solution to
which acetic acid has been added to adjust pH
(information on buffers can be found in section
11.5.2). This should be followed by a neutral
aqueous rinse or spit clean, followed by an
aromatic hydrocarbon rinse if Triton X-100 or
XL-80N has been included in the formulation
(Stavroudis and Blank, 1990).
Aqueous cleaning systems can be expected
to swell and possibly leach water-sensitive
materials. Because water is a poor solubilizer
of oil-based paint, aqueous cleaning systems
were originally thought to avoid the swelling
and leaching of oil paint substrates that occur
as a side effect of solvent cleaning. Whilst it is
undoubtedly true that swelling of oil paint
films is virtually eliminated by using aqueous
systems, leaching remains a problem. Research
indicates that the amount of leaching by resin
and bile soaps is roughly equivalent to typical
solvent cleaning formulations, although most
leaching occurred as a result of rinsing procedures
rather than from the soaps themselves
(Ford and Byrne, 1991). Other research has
indicated that abietate gel leached slightly less
than solvents such as hexane, toluene or acetone
(Tsang and Erhardt, 1992). Factors that
can affect the amount of detergent residues
that are deposited during treatment or cleared
in a rinse procedure are discussed in section
11.5.4.
Conserving other materials II 751
Removal of synthetic varnishes
Modern synthetic varnishes may have been
applied to historic pieces, or may represent the
original finish, for example on twentieth and
twenty-first century objects. As with natural
resin varnishes, the solubility parameters of
most synthetic coatings change as they age.
Many materials (both traditional and modern)
applied to furniture have a tendency to
crosslink. They can be difficult to resolubilize
using solvents and may require a different
strategy for removal. Incorporating surfactants
may aid in dispersing such coatings.
Polyurethane, for example, will swell in aromatic
solvents, so an aromatic solvent gel may
be effective (Landrey et al., 1988). Some synthetic
coatings, for example acrylics, don’t necessarily
oxidize, so the traditional approach of
increasing the polarity of a solvent blend is less
likely to be successful for removing them. In
some cases non-polar solvents may be successful
in removing such coatings, particularly
in conjunction with a surfactant. As with all
cleaning or varnish removal, it is helpful to
understand the forces holding the coating
together, and then formulate a strategy based
on that particular polymeric material.
16.6.4 Removal of overpaint
Removal of old overpaint can be problematic,
particularly where the retouch has the same
binding medium as the original surface and
was not isolated from it. In cases where overpaint
is comprised of natural materials such as
oils or resins, the strategy of swelling or dissolving
overpaint follows the principles used
for the solvent removal of varnishes. Standard
solvents and mixtures (e.g. white spirit, xylene,
IMS, acetone) may be successful. Mechanical
methods may be successful in some cases, or
may be required to reduce the amount of overpaint
before other methods are used.
Mechanical methods may also be used in combination
with solvent-based solutions. In some
cases may be possible to cleave an overlying
layer from an underlying layer. It may be possible,
by understanding the chemical nature of
the materials involved, to develop a removal
strategy on the basis of the specific materials
present (Wolbers et al., 1990).
The incorporation of pigments or metal soaps
used as dispersing agents can make overpaint