Reprinted with permission from the Northeast Document Conservation Center
There are currently five ways to dry wet books and records. All have undergone at least minimal testing under emergency conditions; several have been used extensively. These are described to assit you in making the est choice given your circumstances: cause of damage, level of damage numbers involved, rarity/scarcity, personnel available, budget available, drying service available. Advice from a conservator or preservation administrator experienced in disaster recovery can be helpful before making the final selection(s) Successful recovery operations have proven that it is less expensive to dry original collections than to replace them, even if they are replaceable.
It is important to understand that no drying method restores materials. They will never be in better condition than they are when drying begins. If time must be taken to make critical decisions, books and records should be frozen to reduce physical distortion and biological contamination while decisions are made.
Air Drying. Air drying is the oldest and most common method of dealing with wet books and records. It can be employed for one item or many, but is more suitable for small numbers of damp or slightly wet books and documents. Because it requires no special equipment, it is often seen as an inexpensive method of drying. But it is extremely labor-intensive, can occupy a great deal of space, and can result in badly distorted bindings and textblocks. It is seldom successful for drying bound, coated paper. Book and paper conservators should always be consulted for the drying of rare or unique materials. they may choose to air dry items or may suggest one of the other alternatives.
Dehumidification. This is the newest method to gain credibility in the library and archival world although it has been used for many years to dry out buildings and the holds of ships. Large, commercial dehumidifiers are brought into the facility with all collections, equipment, and furnishing left in place. Temperature and humidity can be carefully controlled to specifications. Additional testing is being undertaken but the technique is certainly successful for damp or moderately wet books, even those with coated paper, as long as the processis initiated before swelling and adhesive have taken place. The number of items is limited only by the amount of equipment available and the expertise of the equipment operators. This method has the advantage of leaving the materials in place on the shelves and in storage boxes, eliminating the costly step of removal to a freezer or vacuum chamber.
Freezer Drying. Books and records that are only damp or moderately wet may be dried successfully in a self-defrosting blast freezer if left there long enough. Materials should be placed in the freezer as soon as possible after water damage. Books will dry best if their bindings are supported firmly to inhibit initial swelling. The equipment should have the capacity to freeze very quickly and temperatures must be below -10 F to reduce distortion and to facilitate drying. Documents may be placed in the freezer in stacks or may be spread out for faster drying. Expect this method to take from several weeks to several months, depending upon the temperature of the freezer and the extent of the water damage. However, caution is advised: with this method leaves of coated paper may adhere to one another.
Vacuum Thermal Drying. Books and records may be dried in a vacuum thermal drying chamber into which they are placed either wet or frozen. The vacuum is drawn, heat is introduced, and the materials are dried above 32 F. This means that the materials stay wet while they dry. It is a very acceptable manner of drying wet records, but often produces extreme distortions in books, and almost always causes blocking (adhesion) of coated paper. For large quantities of materials it is easier than air drying, and almost always more cost-effective. However, extensive rebinding or recasing of books should be expected. This method is a solution for materials that have suffered extensive water damage.
Vacuum Freeze Drying. This process calls for very sophisticated equipment and is especially suitable for large numbers of very wet books and records as well as for coated paper. Books and records are placed in a vacuum chamber frozen. The vacuum is pulled, a source of heat introduced, and the collections, dried at temperatures below 32 F, remain frozen. The physical process known as sublimation takes place i.e., ice crystals vaporize without melting. This means that there is no additional swelling or distortion beyond that incurred before the materials were placed in the chamber.
Coated paper will dry well if it has been frozen or placed in the chamber within six hours after getting wet. Otherwise it may well be lost. Rare and unique materials can be dried successfully this way, but leathers and vellums may not survive. Photographs should be vacuum freeze-dried unless no other possibility exists. Consult a photographic conservator. Although this method may initially appear to be more expensive due to the equipment required, the results are often so satisfactory that additional funds for rebinding are not necessary, and mud, dirt and/or soot is lifted to the surface, making cleaning less time consuming. If only a few books are dried, vacuum freeze drying can indeed be expensive. However, companies that offer this service are often willing to dry one client’s small group of books with another clients larger group, thus reducing the per-book cost and making hte process affordable when only a few books need to be dried.
How to Air Dry Wet Records
Wet records may be air dried if care is taken to follow guidelines suggested by preservation experts. The technique is most suitable for small numbers of records that are damp or water-damaged only around the edges. If there are hundreds of single pages, or if the water damage is severe, other methods of drying will be more satisfactory
and cost-effective. Stacks of documents on coated, or shiny, paper must be separated immediately to prevent adhesion, or they must be frozen to await a later drying decision. Care must be taken with water-soluble inks as well. Records with running or blurred inks should be frozen immediately to preserve the written record. After drying, conservators can be contacted for advice and assistance.
If records must be air dried, the following steps will help achieve satisfactory results. Wet paper is extremely fragile and easily torn or damaged, so care must be exercised. Once wet, records will never look the same, and at least some cockling or distortion should be expected.
1. Secure a clean, dry environment where the temperature and humidity are as low as possible. The temperature must be below 70 F and the humidity below 50%, or mold will probably develop and distortion will be extreme.
2. Keep the air moving at all times using fans in the drying area. This will accelerate the drying process and discourage the growth of mold. If materials are dried outside, remember that prolonged exposure to direct sunlight may fade inks and accelerate the aging of paper. Be aware that breezes can blow away single records. Train fans into the air and away from the drying records.
3. Single leaves can be laid out on tables, floors, and other flat surfaces protected if necessary by paper towels or clean, unprinted newsprint. Or clotheslines may be strung close together and records laid across them for drying.
4. If records are printed on coated paper, they must be separated from one another to prevent them from sticking together. This is a tedious process, which requires skill and patience. Practice ahead of time will prove useful. Place a piece of polyester film on the stack of records. Rub it gently down on the top document then slowly lift the film while at the same time peeling off the top sheet. Hang the polyester film up to dry on the clothesline using clothes-pins. As the record tries, it will separate from the surface of the film. Before it falls, remove it and allow it to finish drying on a flat surface.
5. Once dry, records may be rehoused in clean folders and boxes. Or they may be photocopied or reformatted on microfilm or fiche. Dried records will always occupy more space than ones that have not been water-damaged.