Freezing And Drying Of Books, Paper And Photographic Materials

The following definitions in this resource have been compiled from CCAHA Disaster Recovery bulletins: Salvaging Books, Salvaging Art on Paper, and Salvaging Photographs. Please see the individual salvage brochures for instructions and detailed discussions about the pros and cons of the various methods in relation to the particular class of materials. The bulletins are available in PDF format at


Because there is no standardized terminology for drying methods among disaster recovery vendors, beware of semantic confusion. Terms like vacuum thermal-drying, dehumidification-drying, and freezer-drying may be unfamiliar to vendors, or they simply may use another term. Before calling a service provider, be sure you can explain the service you are seeking. This is particularly important with services like freeze-drying; the term could correctly be used to refer either to drying through sublimation or to freeze-thaw-evaporative-drying in a vacuum chamber (listed here as vacuum thermal-drying). While the term freeze-drying can be used to describe both processes, the second option can have very different and potentially negative results on collections materials.

Before contracting with a drying service, there are important preliminary considerations.

  • If you are unfamiliar with the drying service a vendor offers you, ask for a detailed explanation. Take good notes and be sure you understand and are satisfied with the process before you agree to anything.
  • Document the disaster in photographs and in writing. This is important both for insurance claims and to establish the condition of the collection before the contracted service. Document the collection’s condition both immediately after the disaster and before the collection is turned over to a drying contractor. The documentation should include condition, appearance, and presence of mold.
  • Write a letter of agreement to be signed both by you and the contractor that details the services to be provided, stipulates that frozen materials will not be allowed to thaw before drying, and states when the materials are to be returned.

In the PDF below, a summary table with the different materials and related recovery methods is presented, along with their advantages and disadvantages for conservation purposes.

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