O bjects at the J. Paul Getty M useum

O bjects at the J. Paul Getty M useum

In 1988, when Gordon Hanlon came to the J. Paul Getty Museum in Malibu, California, to work as a conservator in the Decorative Arts Conservation Depart-

ment, he found that problems with insect infestation occurred infrequently. New acquisitions, primarily furniture from Europe, were fumigated and made free of

insects close to their point of origin prior to shipment. When an in-house need for disinfestation arose, objects were treated with methyl bromide at a fumiga- tion facility about thirty miles away. However, a variety of concerns about transportation, security, safety, and cost of this procedure were raised, making it desirable to find a procedure that could be done safely at the museum. These concerns came to a focus in 1991 when a 220-year-old French fire screen made of walnut was found to have a hole penetrating the wood with a small amount of frass beneath the hole. A pile of eggs was also uncovered, evidence of an infestation by furniture beetles. This event occurred at about the time that work- ers at the Getty Conservation Institute were demonstrating the effectiveness of

nitrogen anoxia, and Rust and Kennedy were gathering data on the conditions generally needed to kill all life stages of the most common museum pests.

Hanlon decided to try nitrogen anoxia on the fire screen. He believed that he could maintain the required treatment conditions by building a container around the object and purging the system with humidified nitrogen. An Aclar pouch was

Chapter 6

Figure 6.1

Italian armchair under treatment.

custom-tailored into a tapered, almost triangular, shape to fit the fire screen. The construction, done with a small, hand heat sealer, took only about two hours, although Hanlon believes that a larger bar sealer of the type used in paper conservation would have shortened the construction time. Dynamic nitrogen anoxia, as previously noted, requires humidification. This was done using the split-stream humidifier described in chapter 4 as well as Arten gel as a humidity buffer. The system was first flushed rapidly with nitrogen containing only 5 ppm oxygen until the oxygen level in the container fell to 1000 ppm. The nitrogen

flow was then decreased and adjusted to maintain the oxygen concentration at 1000 ppm, and this was monitored by aTeledyne model 316 trace-oxygen ana- lyzer over a two-week period.

Following the successful elimination of insects from the fire screen, the Aclar bag was reused to treat a small French console table that was infested with wood- boring insects. The third object in this early series of treatments was substantially larger, a 260-year-old Italian armchair that was infested with furniture beetles.

A 1.5 m 3 container, again of Aclar laminate, was constructed to fit around the chair, which was placed on a table holding much of the monitoring equipment

and the three-bottle split-stream humidifier (Fig. 6.1). The temperature and RH were measured with a Vaisala HMP 133Y monitor. The oxygen level was fol-

lowed with two instruments: a GC Industries oxygen monitor, model GS502, with a 33-475 sensor that provides data down to 1000 ppm; and the Teledyne

model 316 analyzer, which can determine oxygen levels to a few parts per mil- lion. Data were collected by a Campbell Scientific 21X data logger and stored.

The careful, continuous recording of oxygen concentrations in this study pro- vided insight into the mechanics of the gas flow needed to achieve and maintain oxygen levels below 1000 ppm during a dynamic run. In a preliminary experi-

ment to determine the rate of oxygen leakage into the system, the bag holding the chair was first purged with nitrogen containing 5 ppm oxygen at 55% RH

at a high input rate of 7 l min - 1 , while temperature, oxygen concentration, and RH were monitored. This lowered the oxygen concentration to 400 ppm in

40 hours. At that point, the inlet and outlet valves were closed, and a slight bulging of the treatment container indicated that the pressure inside was some- what higher than the pressure outside. Leakage began to equalize the pressures over 24 hours. This corresponded to a slow increase in oxygen concentration over this period, followed by a faster increase over the ensuing 72 hours until

Anoxia Treatment in a Dynamic M ode

Figure 6.2

Determination of oxygen leakage rate during treatment of Italian armchair.

Oxygen ppm

Time, hours

the pressures roughly equalized (Fig. 6.2). During this preliminary experiment, the oxygen leak rate was determined to be 490 ppm (735 ml) per day.

During the actual treatment of the chair, the bag was initially purged with nitro- gen at 7 l min -1 for 60 hours, and this brought the oxygen concentration to 800 ppm (Fig. 6.3). The nitrogen flow was then decreased to 0.5 l min -1 , and the exit valve was partly closed. The oxygen concentration remained relatively con- stant, increasing to only 900 ppm after an additional 120 hours. This demon- strated that a low flow rate of 720 l per day into a 1500 l bag can compensate for the leakage of 735 ml of oxygen per day into the bag. It was necessary to change the nitrogen cylinder at this point, and the flow was increased to

2.0 l min -1 , where it was maintained for the rest of the 2-week treatment. This higher rate brought the oxygen down to 400 ppm, a level where anoxia is even

more effective than the recommended 1000 ppm for dispatching insects. Failure to find any sign of insect life after four years posttreatment is proof of the suc-

cessful disinfestation of the fire screen, the wooden table, and the armchair. This led Hanlon to conclude that a continuous nitrogen flow into a large Aclar plastic bag can maintain an oxygen concentration well below 1000 ppm for the dura- tion of treatment and provide a highly effective procedure for pest control.

Figure 6.3

Oxygen concentration in treatment bag during disinfestation procedure.

7.0 liters per minute Oxygen

ppm