The Structural Conservation of Panel Paintings

As a direct result of concerns about the possible health risks, environmen-

tal impact, and damage to objects posed by toxic gases and other chemical

treatments for controlling insect infestation, a growing number of research

studies have investigated alternative treatments employing low oxygen

environments. The stored products industry has used and published infor-

mation on modified atmospheres to control insect pests in stored grains

and food for several years (Bailey and Banks 1980). These studies, however,

center on insect species that are not directly relevant to museum objects,

and the aim of the studies is to control rather than to eradicate the insect

infestation. More recent studies, which have focused on insect species that

are known to be a problem for the museum community, discuss the effects

of low-oxygen atmospheres on the mortality of several insect species

(Valentin and Preusser 1990; Gilberg 1989, 1991; Rust et al. 1996; Valentin

1990). These investigations have shown the efficacy of low-oxygen envi-

ronments—which use inert gases such as nitrogen, argon, and helium—to

kill all life stages of the insect species studied and have quantified the rela-

tionship of temperature and relative humidity (RH) conditions to the mor-

tality rate. A study sponsored by the Getty Conservation Institute was

performed at the University of California, Riverside, where Rust and

coworkers (1996) evaluated the mortality of all life stages of ten com-

monly found insect species at 55% RH and 25.5 °C in a nitrogen atmos-

phere having less than 0.1% oxygen. The time required for 100% kill

varied from 3 hours f or the adult fire brat (Thermobia domestica) to 192

hours for the eggs of the cigarette beetle (Lasioderma serricorne). Several

independent studies have examined the mortality rates at lowoxygen

concentrations of wood-boring species, including the furniture beetle

(Anobium punctatum), the powderpost beetle (Lyctus brunneum), the western

drywood termite (Incisitermes minor), and the house longhorn beetle

(Hylotrupes bajulus). All of these studies prove the efficacy of low-oxygen

environments in killing the life stages ofthese species.

Based on this research, the Getty Conservation Institute and the

J. Paul Getty Museum have perfected a number of methods for creating

and maintaining a low-oxygen environment for the treatment of insect

infestations. These methods are especially applicable to panel paintings

and can also be used to treat infested picture frames and stretchers of

canvas paintings. This article describes how these methods are applied to

maintain an oxygen concentration of less than 0.1% and the desired RH

for the duration of the treatment.

The two basic requirements for insect eradication using low-oxygen atmos-

pheres are to create a method of encapsulating the object to be treated and

to reduce the oxygen concentration within this enclosure to 0.1% or less.

Encapsulation of the infested object: Bag construction

The simplest method of encapsulating an object is to use plastic sheeting,

which is heat-sealed to form a bag or pouch that encloses the panel to be

treated. However, the oxygen permeability of various plastic sheeting

varies considerably, and it is critical to select a plastic film with the lowest

possible oxygen permeability to maintain the low-oxygen concentration

within the bag for the duration of the treatment (Burke 1992). The

authors selected Aclar (polychlorotrifluoroethylene) composite film with

Practical Application

Theory of Modified

Atmospheres

70 Hanlon and Daniel