General Procedures

General Procedures

The most widely used procedure for the treatment of infested objects is anoxia in barrier-film bags. Quite suitable bags may be purchased from a growing num-

ber of suppliers who have been upgrading the quality of their products and are providing bags based on the latest, most oxygen-impermeable barrier compos- ites available from film fabricators. When these bags are purchased, it is advis- able to obtain a statement of specifications for the film properties, especially for oxygen permeability. Treatment pouches can also be handmade from the same barrier-film composites that are sold in rolls.

Making bags by hand, instead of purchasing them, may seem like a major investment in time, and perhaps too much trouble. But many conservators, once they have learned the procedures and techniques, prefer to buy rolls of film and make their own bags. The procedure is simple and, with time, so is the execu- tion. The first step is to cut a rectangle of film from a roll that is somewhat larger than twice the desired size of the bag. The rectangle will be doubled over to pre- pare a pouch of the required dimensions. Care should be taken to cut straight lines to produce a true rectangle so that the edges line up precisely. The film should be placed on a flat, horizontal surface with the heat-sealable surface, usually a layer of polypropylene or polyethylene film, face up. The sheet is then doubled over, and a pouch is created by heat-sealing the two side edges, leaving

the top edge open. Finally, the objects to be treated, along with some type of oxygen monitor, are placed in the pouch, and the container is thoroughly purged

with a rapid flow of nitrogen gas introduced via a flexible tube inserted into the open end of the bag. Then, packets of oxygen absorber are placed in the pouch, and the remaining open end is heat-sealed closed. An important step is leak- testing the bag after the objects have been sealed inside. As described in chapter

4, this is done by using a hypodermic syringe to inject into the bag a small amount (a few cubic centimeters) of detectable gas such as 1,1,1,3-tetrachloro- propylene. The puncture hole is sealed with tape, and the nozzle of a halogen leak detector is run over the bag's exterior.

If an opaque, metallized film is used to make the bag, it is not possible to see inside to check the performance of the oxygen monitor. The solution to this, when the monitor is a small-diameter indicator tablet, is to install a small win- dow in the opaque film before the open sheet is converted into a bag. The win- dow is prepared from a small piece of clear barrier film; often the plastic wrapper holding the packets of Ageless is used. A 2-3 cm (1 in.) square opening is cut into the metallized film and covered with a 7-8 cm (3 in.) square of clear barrier film with the heat-sealable surfaces in contact. The envelope containing the Ageless-Eye indicator tablet is taped to this window with the envelope's small openings facing away from the wall. The window is then heat-sealed to the opaque film with a small tacking iron, with appropriate pressure. The window is created 5-10 cm from where the final closing seal will be made. This allows