fibers. As with a damaged gluing surface, decisions must be reached as to
how vigorously the conservator is to intrude in order to make the artifact
whole. These decisions must, by nature, be ad hoc, but there are some
general guidelines for treatment strategies.
The existence of substrate voids, either in the fracture region as
a whole or at the glue line in particular, may contribute to the overall
structural instability of the object. (Whether or not the voids contribute
to further deterioration depends on numerous construction, usage, and
environmental factors outside the scope of this article.) The degree of
instability, along with the anticipated future circumstances of the artifact,
usually determines whether the voids are to be filled or left empty.
In the case ofpanel paintings, the fill must be made to fit the void
exactly. This can be accomplished by either cutting a wood piece to fit the
void precisely, casting flexible thermoset material into the void, filling the
void with an inflexible thermoset material, or using a combination of
these methods. Unless the fill is a tight wood-to-wood system, the gluing
surface should be isolated from the fill with an easily reversible barrier
film, such as animal glue or synthetic resin solution. The author has found
the use of hide glue to be the most convenient and utilitarian material for
this purpose.Treating degraded or failed adhesives
Reactivation of adhesives
Although it is the least intrusive intervention, reactivation unfortunately is
usually among the least successful. Because it involves the use of solvents
or heat, reactivation is limited to cradles or other backing supports of
panel paintings and is not suitable for the panels themselves. By definition
this technique can be applied only to adhesive materials that are thermo-
plastic and not so degraded as to prev ent any useful re-formation of an
adhering film. Even when successful, this approach rarely yields a strong
bond, and the object may be incapable of fulfilling its normal use.
Reactivation is most commonly applied to aged hide glue, but it
can also be applied to synthetic solvent-based adhesives, which, as men-
tioned above, are frequently present in artifacts as part of a previous
attempt to rectify damage. Reactivation is usually done when other meth-
ods are not possible, but the resulting bond may not be strong enough to
allow normal use of the object. With respect to panel paintings, there is
also the very real possibility of damaging the decorative surface of the
object; solvents that dissolve polymeric adhesives will also act as paint
removers for many coatings.Introduction of a new adhesive
Amore intrusive repair method, but one with a greater chance of success
than reactivation, involves adding new adhesive to the glue line to aug-
ment failing adhesives. The usual objective is to fill any voids completely,
thereby providing the necessary degree of strength and the greatest pos-
sible stability and durability. The primary constraint on this technique is
that the newly introduced adhesive must be compatible with and bond to
the existing adhesive.
In general, this method of stabilizing the structure is used only for
adhesives that are readily soluble in the same solvent and thus can meld
together to form a cohesive bond. Hide glue is most commonly used for84 Williams