The most effective method of achieving maximum penetration is
to use vacuum impregnation, which can be a practical method, except in
the case of very large objects (Schaffer1974). The easiest method is to
draw a vacuum while the object is submerged in consolidant solution
within the vacuum chamber; the vacuum is continued until most of the
air has been drawn from the porous wood structure. The vacuum is then
released, causing atmospheric pressure to push the consolidant solution
into the wood. For maximum results, the vacuum should be drawn first
and the consolidant solution subsequently introduced to cover the object
while under vacuum, so that the solution does not impede the removal of
air from within the wood. However, this approach would require elaborate
equipment, which would probably not be justified in most cases. Some
parts ofthe fire engine previously mentioned were treated by vacuum
impregnation, using a solution of20% Butvar B90 in ethanol. The rela-
tively high concentration was chosen to maximize loading, and the vac-
uum impregnation method was relied upon to achieve sufficient
penetration (Barclay 1981).
While most of the examples given above are of consolidation
treatments with soluble resins, the methods of application described can
be executed with any type of liquid used for consolidation. For panel
paintings it is difficult to visualize much other than brush treatments from
the back. A possible exception would be soaking the panel face up in a
shallowpan containing a small amount of consolidant. In any case, care
must be taken that the consolidant does not reach either the ground or
thepaint layers—or at least, if it should reach the ground, that it does not
change the ground’s characteristics.
When solvents are used to introduce consolidants into deterio-
rated wood, there is potential concern that during solvent removal, evapo-
ration from the surface will result in reverse migration of consolidant from
the interior toward the object’s surface (Payton 1984). When solvents are
used solely to improve penetration of thermosetting resins, reverse migra-
tion can be reduced or eliminated by the prevention of solvent evaporation
until the resin has been cured and fixed within the object (Selwitz 1992).
Migration ofwater-soluble wood extractives to the wood surface can be
observed in the course of normal lumber drying (Anderson et al. 1960).
Reverse migration of soluble resins during solvent removal in stone consoli-
dation can be mitigated by reduction of the rate of drying (Domaslowski
1988). Terziev and coworkers found that water-soluble sugars present in
the sap of freshly cut wood would undergo significant redistribution
during drying and that much more sugar migrates toward the surface
during fast, as compared to slow, drying schedules (Terziev, Boutelje,
and Söderström 1993). Samples of deteriorated Douglas-fir treated with
Acryloid B72, Butvar B98, or Butvar B90 had lower bending strengths
when dried very slowly, as compared to samples dried more rapidly in the
open air (Wang and Schniewind 1985). The samples of B98 and B72 dried
in the open air were examined by scanning electron microscopy to deter-
mine consolidant distribution. The results showed that the consolidant
was more heavily concentrated near the surface than in the core. Since the
samples had originally been completely saturated with consolidant solu-
tion, this was definite evidence of reverse migration (Schniewind and
Eastman 1994). While the slowly dried samples were not examined for
consolidant distribution, the observation of lower bending strength is
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