Treatment in Small Pouches

Lesley Bone, conservator at the Fine Arts Museums of San Francisco, California, has been using the dynamic approach to nitrogen anoxia as her standard treatment. Bone became aware of its potential for treating infestation problems from her association in the early 1990s with Mark Gilberg, who was then working in the San Francisco area. Anoxic treatments at the Fine Arts Museums began in 1995 using reclosable zipper bags based on Aclar. The 1.2 m 2 bags were sup- plied by Conservation Support Systems. In a typical setup operation at the museum, prepurified nitrogen is first passed through a bubbler system to bring the gas to 50% RH. It then passes into the treatment bag via tubing attached by an O-ring Swagelok fitting. The bag also contains a low-range Teledyne oxygen sensor. The fitting is attached to an area of the film surface that has been strengthened with overlays of a stout transparent tape. After the infested object is placed in the bag, the zipper is only partially closed, to allow a rapid nitrogen inflow that brings the oxygen concentration down to 1000 ppm. The zipper is then sealed as tightly as possible, and the nitrogen flow is slowed to maintain the oxygen level below 1000 ppm. Runs of 2 weeks have been sufficient to kill species endemic to the museum's collection, namely powderpost beetles and webbing clothes moths. Incoming wooden ethnographic materials—for example, African carvings—may contain termites and are routinely treated in

the same manner. Bone has made bags by hand from Marvelseal film. But she finds this to be more work than using zippered bags, which can be reused about three or four times.

David Casebolt, museum specialist in conservation with the San Francisco Mari- time National Park, has used a variety of procedures to keep the park's archival

collection free of insects. These include anoxia in refitted and gasketed alumi- num containers from navy surplus, as well as oxygen deprivation with Ageless alone when treating small objects in handmade pouches. His facility is heavily involved with archival material that is most frequently infested with silverfish.

The powderpost beetle, beetles in the Dermestidae family, and termites are other species often encountered. Casebolt uses nitrogen anoxia in the dynamic

mode for more sizable objects, which go into larger bags. A major area of acqui- sition for the maritime complex is archival collections, which are often received

in a damp condition. A bubbler system, which would normally be used in the dynamic mode, is usually not employed with these collections. In this way, the anoxia treatment is also used to dry the collection.

Christoph Reichmuth has used the dynamic method, which he calls "nitrogen flow fumigation," for projects ranging from studies of the effect of temperature on kill time to treatments of wooden sculpture and other objects. The mortality

rate studies were directed at webbing clothes moths, subterranean termites, and

a variety of beetles that are common museum pests (Reichmuth et al. 1993;

Unger, Linger, and Reichmuth 1992). For these studies, infested objects as well as control insect specimens were placed in polyethylene bags that were purged one to three times with nitrogen. The pouches were inflated and kept at a 1% oxygen level with a slow nitrogen inflow at 5-10 Pa. The RH was held at 55- 60% with aqueous solutions of glucose or calcium nitrate. The minimum kill times recorded by Reichmuth were substantially longer than those found by Valentín or Rust and Kennedy. However, he had used a higher oxygen level and lower temperatures than the other investigators. For example, Reichmuth deter- mined a kill time of over 500 hours for the powderpost beetle at 25 °C and 1% oxygen, while Rust and Kennedy indicated that only 120 hours are needed at 0.1% oxygen at the same temperature. For the furniture beetle, Valentín found that 168 hours were needed to eliminate all life stages at 30 °C with 0.1% oxygen. Reichmuth required 500 hours at 35 °C and 1% oxygen; dropping the temperature from 35 to 16 °C led to an increase in treatment time of 2 weeks, for a total treatment time of 836 hours. Quite clearly, higher oxygen concentrations are responsible for extremely long treatment times. Additionally, as has now been thoroughly established, lower temperatures extend the treatment period even further.

Reichmuth describes several other successful treatments achieved with nitrogen flow fumigation, albeit with excessively long exposure times at the high oxygen level he uses. Two sculptures and a painting—all large, wooden pieces infested with furniture beetles—were rid of pests by runs conducted at 25 °C for

5 weeks. The painting, by Lucas Cranach the Younger, is a portrayal of the Last Supper on a 2.1 × 2.6 m wooden table. One of the treated sculptures was

a polychrome altar, a shrine to the crowning of Mary. The altar holds three figures, each 1.1m high. The other sculpture was a Pietà, without mounting, made of limewood and measuring 85 × 55 cm. For these treatments, control samples of all life stages of the furniture beetle—some encased in wood to examine the diffusion of nitrogen into this medium—were added to the con- tainer along with the infested object. The control insects served as monitors of the treatment's effectiveness. Reichmuth noted that the disadvantages of nitrogen fumigation were the long treatment time at 1% oxygen and the lack of a

residual protective effect.

Treatment in Small Pouches