Preservation

Efficacy of Various Drying Methods

Hilary A. Kaplan and Kathleen A. Ludwig
Document Conservation Laboratory
National Archives and Records Administration

In-House Drying

Air Drying has been the method of choice for small water-related incidents at the National Archives. In this study, we departed from our customary response so that all boxes would be handled in a similar manner--materials to be air-dried were frozen just like those materials to be sent off-site for commercial processes. Freezing might be a necessary step following a large-scale disaster. Since air-drying can require vast surface areas not readily available, materials may be frozen and thawed in manageable amounts as drying space becomes available. A frozen water-saturated records storage box (.0339 cubic meters) can take up to 24 or more hours to completely thaw at room temperature.

Archives staff have had a great deal of experience air-drying records. Air-drying offers us the security and privacy controls that are often required for our holdings. It allows us to isolate materials that may need special handling, such as coated papers, parchment, or photographic materials, and provides direct monitoring of original order, allowing us to maintain intellectual control.

Air-drying pre-supposes that ample space and trained personnel are available for carrying out this labor-intensive activity. Other drying methods may be preferable when the quantity of damaged materials is great and there is a lack of available space or personnel.

After the records in our study completely thawed, items were set onto tables lined with absorbent blotting paper. Bound materials that could not be safely supported upright were laid flat on blotting paper for drying. Pages were turned periodically during the two days of air-drying. Stacks of cards or groupings of papers were turned to expose wet surfaces throughout the process.

During the air-drying process, attention was focussed on maintaining original order of the folders and their contents. When possible, it is very helpful to have the same individual unpack wet and reassemble the same dried materials to maintain close control over original order. Items with coated paper were individually interleaved with sheets of a polyester non-woven fabric, Holytex™ or Remay™, to prevent blocking of the pages upon drying.

Dupont Clysar™ EHC shrink-wrap (a stable industrial plastic film adapted for preservation packaging and transport) and Mylar™D, and Melinex™ 516 polyester films (used in protective L-sleeves and encapsulations) are typically found in records at the National Archives. For effective air-drying, completely remove plastic films from water- damaged sheets and volumes.

The ambient conditions within the air-drying area were monitored with a Rotronic Data Logger and air-drying was successfully completed in two days. Temperature readings were just above 21° Celsius (70°F). The relative humidity fluctuated between 20-30%.

Dehumidification-drying is often cited in the literature for its excellent results in drying damp collections. It allows access to the materials during the drying process, if desired or required. Dehumidification can be performed on-site with equipment rented from a vendor. Drying procedures can be carried out in-house by institutional staff or by professionals from the drying service. Items may also be sent directly to the vendor's location for the same services. Drying is completed within several days, depending on the initial degree of wetness of materials.

Dehumidification in an on-site drying chamber is an attractive option when dealing with large quantities of content sensitive materials. As a chamber was already up and running at a NARA facility, we included dehumidification as a drying method to be examined. The results of drying conducted by our staff were then compared to those carried out by a vendor off-site using the same method. To confine requisite dry air, a chamber had been constructed in a loading dock bays. Dehumidification equipment was rented and installed by the contractor and drying procedures were carried out by Archives staff.

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