The Structural Conservation of Panel Paintings

3. No internal stresses should be imparted to the object by
   shrinkage of the consolidant upon solidification. In extreme
   cases, such stresses could cause internal ruptures and distor-
   tions of the object.


4. The consolidant should be compatible with other materials,
   such as paint, that are either already present or might be added
   later during additional treatments.


5. The treatment should be reversible. Grattan felt that reversibil-
   ity was necessary at least in the short term, if for no other rea-
   son than to allow correction of any mishaps that might occur
   during treatment (Grattan 1980).


6. The consolidant should be an effective strengthener.


7. The treatment should be capable of good penetration and
   result in ample deposition of consolidant.

The order of this list is somewhat arbitrary, because priorities

vary with each case. For panel paintings, compatibility with other materials

is of major importance because any interference with the ground or the

paint layers will not be tolerated. It should also be noted that even though

some of the first five items are couched in positive terms, they all refer to

characteristics that consolidants should not have. They should not deterio-

rate, change appearance, cause stresses, interfere with associated materials,

or be permanentlyfixed. Only the last two refer to positive effects, and in a

sense, the sixth item implies the seventh. Thus, this review of the require-

ments of consolidants stresses the importance ofmaking sure that a con-

solidation treatment will not harm the object.

Types of consolidants may be divided into two categories: natural and syn-

thetic materials. Comprehensive and detailed overviews of various types of

consolidants for deteriorated wood are given in the literature (Unger and

Unger 1987; Unger 1988).

Natural materials

Natural materials include hide glues, waxes, resins, and cellulose deriva-

tives. Except for cellulose derivatives, which did not become available until

the end of the nineteenth century, natural materials are also the tradition-

ally used materials.

Hide glues have several significant disadvantages as consolidants:

they do not penetrate well into the wood structure; they will shrink and

swell in response to humidity fluctuations; they are not moisture resistant;

and they will become brittle over time.

Waxes, specifically beeswax and paraffin, have been used as consoli-

dants in the past either alone or as wax-resin mixtures. Using wax is a disad-

vantage because treated objects look greasy, attract dust, and darken with

age. Furthermore, the strengthening that can be achieved is minimal. Unger

refers to several examples of wooden panels treated with wax or wax-resin

mixtures. Once applied, the wax is nearly impossible to remove entirely;

therefore, residues may interfere with later treatments (Unger 1988).

Natural resins such as damar, shellac, and rosin have been used

extensively in the past. However, these resins produce only moderate

Types ofConsolidants

90 Schniewind