Thanks to Martha Battle Jackson, Curator for North Carolina Historic Sites and one of C2C’s “Collections Management Bootcamp” instructors, for providing the following advice on freezing that she learned from a past AAM conference session on Integrated Pest Management.
Freezing is an effective method to kill insect eggs and larvae within an object and also to stall moisture-related deterioration. The key principles to follow when freezing objects are:
- Freeze to -20º C (-5º F).
- Freeze quickly, thaw slowly to prevent insects from developing “freezer resistance.”
- Remove as much frass as possible.
- Bag object in a sealed polyethylene bag.
- Extract as much air as possible to reduce water vapor.
- Store at room temperature before freezing.
- Use a manual defrost, such as a Sears Kenmore (can go to -28º C, has a quick freeze option, and takes four hours to reach -20º C); auto defrost freezers use heat which allows the insects to adjust to changes in temperature.
- Use an electronic data logger to monitor temperature and humidity changes; insert a probe as close to the core of the object as possible.
- Non-porous materials, such as metals, can develop condensation if in contact with organic materials; put a buffer between materials. Cotton batting will reduce freezer effects.
- Keep at -20º C for 48 hours.
- Thaw for 8 hours @ 68º F -70º F.
- Follow with second freezing cycle of 48 hours (“double reduction method”).
- Allow to come to room temperature before opening.
- Continue to monitor objects to make sure there is no further evidence of pests.
Objects that can be frozen include textiles, furs, skins, leather, wood, and books. Do not freeze composite objects, objects with painted or illuminated surfaces, or fragile objects without consulting a conservator first.
Conservators have studied whether freezing has harmful effects on a variety of materials. Dimensional changes in wood and delamination (especially in the cases of veneer and glued joints) are risks. In many cases, however, the risk to the object from pests or mold is far greater and freezing is an appropriate salvage method. Conservator Ellen Carrlee conducted an observational study of the effects of freezing a large and varied collection of ethnographic objects. Among objects that conservators deemed stable enough to try freezing, there were no noticeable negative effects from the treatment.
Posted on April 9, 2013, in collections care, collections management, Connecting to Collections, historic sites, workshops and tagged AAM, Ellen Carrlee, Integrated Pest Management, Martha Battle Jackson, mold, museumpests.net. Bookmark the permalink. Leave a comment.