Efficacy of Various Drying Methods
Hilary A. Kaplan and Kathleen A. Ludwig
Document Conservation Laboratory
National Archives and Records Administration
Vacuum freeze-drying is the drying method of choice for large quantities of wet materials. It results in the least amount of distortion, precluding the need to re-house or re-label most materials. Freezing immobilizes water to minimize corrosion from metal fasteners. Soluble media will not move once the document is frozen or during subsequent drying, and coated papers do not stick. Even items enclosed in plastic need not be removed from their original housings or enclosures, minimizing disruption of original order or potential loss. Existing labels are preserved.
While advantages generally outweigh disadvantages, vacuum freeze-drying also has downsides. No access to materials during the frozen state or drying process is available. Your materials may be included with other records in the drying chamber. While the cost for freeze-drying appears comparable to other processes, materials must be kept frozen, and the logistics of keeping materials frozen during transport is an additional cost factor. This may make freeze-drying small quantities of materials expensive. Increase delamination in cellulose nitrate coated architectural drawings was noted.
Being an informed consumer about the recovery services purchased will help make the best value of limited resources and ultimately yield the most satisfying results from a water-related incident. As a result of our experiences, we have learned how important it is to be as precise as possible at the outset of a project about expectations for a final product. Proprietary processes may offer outstanding final products, but caution is best exercised to ensure that your needs and specifications for what are acceptable and unacceptable methods and materials are assiduously followed. Regardless of technique used, many of the issues raised will be useful in the decision-making process so critical in determining the most appropriate action for a particular group of materials. While the information we accumulated in our review of drying processes has repeatedly proved fruitful, we wish to emphasize that there is no substitute for a building-wide risk assessment and preparedness plan.
The commercial drying industry continues to be responsive to the preservation community, tailoring, improving, and expanding their products and services. We are grateful for their steadfast cooperation in working to minimize loss to cultural property from water-related disasters.
We would like to express our appreciation to Doris Hamburg, Director, Preservation Programs, and Mary Lynn Ritzenthaler, Chief, Document Conservation Laboratory for the mentoring and support as we embarked on the activities associated with this study. We are also indebted to the assistance and encouragement we received from Supervisory Conservator, Catherine Nicholson, and our colleagues in the Document Conservation Laboratory and in Research and Testing. Special thanks to National Archives Staff who donated testing materials, and assisted with this project.
Technical data for polyester films is available at http://www.dupontteijinfilms.com.
Such materials are slowly permeable to moisture over time. Their rates of water
vapor transmission are dependent on film thickness and the environmental conditions
to which they are exposed. After 24 hours of immersion, we witnessed moisture
inside both shrink-wrap and polyester film. This effect is less likely the result
of moisture permeability than a disruption in the integrity of the seal, or
a flaw in the film, such as a small hole. A PowerPoint version of this paper
is available online at the National Archives Website at
List of Suppliers
Hygrolog with LC Display available from Rotronic Instrument Corp., 160 E. Main Street, Huntington, NY 11743, U.S.A., 631-427-3898
Delmhorst P-2000 Paper Moisture Meter with 12 inch blade electrode available from Delmhorst Instrument Company, 51 Indian Lane East P.O. Box 68 Towaco, NJ 07082 USA Phone: 800-222-0638.
Hilary A. Kaplan is a Senior Conservator at the United States National Archives and Records Administration in College Park, Maryland. From 1989 - 2002 she was Conservator and Preservation Services Manager at the Georgia Department of Archives and History. In 1990, she became a Professional Associate of the American Institute for Conservation (AIC), and has served as Secretary of the AIC Board, and advisor for the AIC Archives Project since 2000. Hilary holds degrees in music from Hunter College, and The University of Chicago and received her M.S. and Certificate in Library and Archives Conservation from Columbia University School of Library Service Conservation Education Program. She has taught several workshops on emergency preparedness, response, and recovery on local, regional, and national levels.
Kathleen A. Ludwig is a Senior Conservator at the United States National Archives and Records Administration in College Park, Maryland. From 1984 - 1997 she was an Archives Conservator at the Minnesota Historical Society. She is Professional Associate of the American Institute for Conservation (AIC), and received her M.S. and Certificate in Library and Archives Conservation from Columbia University School of Library Service Conservation Education Program.