4 days needed for this species in the open.

Table 2.5

Environmental conditions used to achieve complete insect mortality in different historic objects exposed to an argon atmosphere (Valentín 1993).

Kill time (days)

A B Infested object size (cm)

Insect species

T (°C) % RH O 2 (% )

Insects in objects Control insects

Books—35 x 25 x 16

30 40 0.02 4 3 Bundled documents—30 x 25 x 15 Drugstore beetle, book beetle

Drugstore beetle, powderpost beetle

30 65 0.02 4 3 Sculpture a —200 x 80 x 52

25 45 0.04 10 4 Sculpture a —130 x 30 x 60

Furniture beetle

25 45 0.03 10 4 Piano a —200 x 100 x 100

Furniture beetle

25 40 0.03 14 4 Panel a —80 x 30 x 15

Furniture beetle

20 50 0.02 7 5 Sculpture a —34 x 25 x 20

Deathwatch beetle

20 50 0.02 10 4 Textiles—135 x 87 x 43

Book beetle, furniture beetle

30 45 0.03 7 2 Panel a —175 x 64 x 35

Black carpet beetle

20 50 0.04 15 14 Frame a —75 x 45 x 15

Old house borer

25 45 0.03 10 10 Plants

Old house borer

40 35 0.03 1 1 a Polychrome

Cigarette beetle

Anoxia as a Conservation Procedure

Anoxia as a Conservation Procedure 16

Chapter 3

An anoxic environment suitable for treatment of infested objects can be achieved in a variety of ways. There are two basic approaches: static and

Methods and dynamic. With the static procedure, the more common approach, objects are

held under high-purity nitrogen or argon in a tightly sealed container with

Materials as little transmission of gas as possible. The oxygen concentration is brought

down to anoxic levels by one of three methods. The container is purged with many exchanges of high-purity nitrogen; the oxygen is removed using large quantities of an oxygen absorber; or a combination of purging and absorption is used. With the alternate dynamic approach, an inert gas is continuously passed through the system during the treatment. Oxygen-free nitrogen or argon is used to flush all of the air out of the container by initially using a high purge rate; then, when an oxygen concentration of less than 1000 ppm is reached, the flow is reduced to that needed to maintain the low oxygen level for the duration of treatment.

The use of an oxygen absorber, by itself, to bring the system to anoxic conditions may be the simplest static procedure. The need for cylinders of nitrogen and humidification systems is avoided. The availability of premade treatment bags with good oxygen-barrier properties and simple clamps that provide gas- tight seals should make disinfestation of cultural property by anoxia available at low cost to almost any institution. This method is best suited for treating limited quantities of small objects. More complex is treatment by nitrogen purging fol- lowed by sealing, with or without the additional use of an oxygen scavenger.

This is the most widely used static method and applies to containments of all shapes and sizes, from small pouches to very large plastic tents as well as rigid metal or plastic chambers, large and small. Humidification is generally used, but not always. The dynamic method has found limited use in special situations, par-

ticularly when the object is too large or too awkwardly located to be enclosed in

a standard container. In this situation, containment is provided by shaping a barrier film around the object. Because unusual or uneven surfaces, such as floor sections, often become part of the containment, it is generally difficult to obtain the required airtightness. However, gas leakage can usually be brought to a level

low enough so that a slow, continuous flow of oxygen-free gas through the system can be maintained effectively and economically. Humidification must be

used with this dynamic approach. What is sometimes considered to be a third procedure, called the static-dynamic method, is an intermediate approach where the purging gas is allowed to pass through the system very slowly.

A number of early workers in the field recognized the possibilities of these treatment methods and described and compared various approaches and systems in research papers. Getty workers (Hanlon et al. 1992; Daniel, Hanlon, and Maekawa 1993) described the characteristics of each method and first proposed the terms static, static-dynamic, and dynamic. Koestler (1992) used a dynamic system to treat a sixteenth-century Andrea del Sarto panel painting that was infested with drywood termites. The panel, resting on a flat table, was covered with a large sheet of barrier film taped to the surface of the table. This containment system was then flushed with humidified gas introduced through a port at one end and allowed to escape through another port at the far end. The treatment was successful but used forty cylinders of gas over twenty days. In the same article, Koestler described three static-dynamic treatments. These used a containment chamber fabricated from a utility storage cart made of heavy-

gauge polyethylene; a Rentokil minifumigation bubble; and handmade pouches of a barrier film made with an ethylene-vinyl acetate copolymer. Treatments with the pouches combined the use of a nitrogen purge and oxygen scavengers.

Valentín (1993) also evaluated the efficacy of the static-dynamic method in three different containment systems: plastic bags of low oxygen permeability; a

tiny (80 cm 3 ), rigid vacuum chamber; and a 6.2 m 3 fumigation bubble made of

tems could provide satisfactory treatment.

Each variation in approach has its own advantages, disadvantages, and special requirements, but there are also critical needs in common. Each requires barrier films with low oxygen permeability; oxygen scavengers with high capacity and good absorption potential; inexpensive nitrogen supplies with a very low oxygen content; and effective methods of containment closure. These will be discussed in detail in the sections that follow.

4 days needed for this species in the open.