Vacuum Freeze Drying This process calls for sophisticated equipment and is especially suitable for large numbers of wet books and records as well as for water-soluble inks and for coated paper. Frozen books and records are placed in a vacuum chamber. The vacuum is pulled, a source of heat introduced, and the collections, dried at temperatures below 32 degrees F, remain frozen. This means that there is no additional wetting, swelling, or distortion beyond that incurred before the frozen materials were placed in the chamber. If materials have been stabilized quickly after becoming wet, very little extra shelf or storage space will be required when they are dry.
Many coated papers can be difficult to dry without adhering once they are wet.
They may then be vacuum freeze dried with a high potential for success. Rare and unique materials can be dried successfully by vacuum freeze drying, but leathers and vellums may not survive. If only a few books are dried, vacuum freeze drying can be expensive. However, companies that offer this service are often willing to dry one client's small group of books with another client's larger group, reducing the per-book cost and making the process affordable. Vacuum Thermal Drying Books and records that are slightly to extensively wet may be dried in a vacuum thermal drying chamber into which they are placed either wet or frozen.