The Structural Conservation of Panel Paintings

T

   a brief review of the types of adhe-

sives used for wooden objects; the conservation treatment of

wooden objects whose elements have undergone structural dam-

age; and the selection and use of adhesives during conservation treat-

ments. Whereas some of the adhesives discussed may not be suitable for

panel paintings, it is important for conservators to be familiar with them

because they are likely to be encountered in previous ill-advised conserva-

tion attempts on panels.

When reviewing the properties, selection, and use ofadhesives

for wood conservation, it is first necessary to answer the question What is

the adhesive supposed to do? Equally important is the converse question,

What should the adhesive notdo? Naturally, this inquiry is part of the

strategy of any particular conservation treatment and, in turn, involves

the evaluation of any ethical issues facing the conservator.

Natural protein adhesives

Prior to the development of synthetic resin adhesives in the early twenti-

eth century, the most common adhesive for wood—indeed, the glue domi-

nant almost to the exclusion of all others—was protein glue. There are a

number of glues that fall into this category of proteinaceous animal by-

products, such as casein, albumin, fish glue, and animal-hide glue.

Casein glue, a powder derived from the curds of acidified skim

milk, forms a water-resistant and heat-resistant adhesive when mixed with

water. Exceedingly strong, casein continues to be used for architectural

laminae and was used in the past to butt-join panels during the original

fabrication of panel paintings. Albumin glue, derived from blood proteins,

is a water-resistant glue used since antiquity. For the ancients, the coagu-

lating process, which drove the adhesion, required the use of fresh blood.

However, when the process for making dried-blood glue was discovered

in the early twentieth century, use of this adhesive became more wide-

spread. Its primary utility was as a water-resistant, heat-activated adhesive

for industrially produced plywood used especially in the fabrication of

early wooden airplanes. Because of its prominence as a plywood adhesive,

this thermoset glue is very often present as the binder in early plywood

panels used as substrates for paintings. Fish glue, another traditional

Adhesives and Their

Properties

79

A Survey of Adhesives for Wood Conservation

Donald C. Williams