Efficacy of Various Drying Methods
Hilary A. Kaplan and Kathleen A. Ludwig
Document Conservation Laboratory
National Archives and Records Administration
Maintaining intellectual control is a far greater challenge when items leave the repository. Be sure to ask contractors to keep original boxes or labels. Only one of a group of four boxes contained a label fragment from its original box. File trace numbers were written on the outside of the box, but no original label information was preserved. We did not explicitly instruct the vendors to save all label information, but erroneously assumed that they would. Was documentation for these samples not preserved because boxes were understood to be test materials? We did explicitly request that our test records be handled in the same manner as true collection items. No subsequent data for lost descriptive information was forthcoming--we did not learn if it had been misplaced or discarded.
Though each box had been identically packed prior to wetting, the order in some boxes was disrupted when they were returned. Sides of original boxes containing information were inserted into new boxes of dried records. While this ensured that all label information was retained, staff needed to open each new box and copy pertinent information to it. In one instance, a pocket-folder filled with documents was returned with items removed from a pocket and inserted as a single grouping within the folder. Original order was disrupted and lost.
Negotiate box quality if dried records cannot be returned in original boxes. Vendors returned our items in new boxes of unknown chemical quality that had been covered with pressure sensitive tape and mailing labels. These boxes were supplied at an additional charge that had not been specified at the outset of the project. One vendor charged 8 dollars per box, or approximately 7 euros. A less expensive transport box is preferred if records are to be transferred upon return to a permanent quality records storage box.
Comparing Physical Results
Equal numbers of printed forms consisting of 1960's machine-made card stock with pen and pencil entries were set side by side to evaluate the increase in volume and degree of cockling. Vacuum freeze-drying produced the least distortion followed by air-drying. Dehumidification drying performed by a vendor off-site and on-site yielded records with the greatest increase in volume and cockling.
Bound volumes behaved much like unrestrained loose pages when dried. The patented vacuum freeze-dry process produced results most like the control. In general, if volumes are misshapen when packed for freeze-drying, the remain in that shape when dry. The patented vacuum freeze-dry process is specifically designed to press volumes back into shape through a compression system in its drying cycle, and often obviates the need for rebinding. shape. Volumes fit back on the shelves as they once were.
The patented process developers have also introduced a Rare Book Drying method in which a volume's text block is dried without desiccating its leather covers, diminishing the likelihood of broken hinges and need for subsequent repair. This approach is, however, more than four times the cost of traditional vacuum freeze-drying-approximately 250 dollars or 230 euros per cubic foot.
Not all books exhibited the same ability to open flat once dried. Both vacuum freeze-dried samples felt stiff and exhibited a slight resistance to opening flat. This may be the binding structure's response to mechanical stress placed on it and its adhesives during the wetting and drying processes.
Books bound with metal fasteners dried satisfactorily. The air-dried volume exhibited the most pronounced distortion. Because of the absence of a hard cover, the book could not be dried vertically and pages were forced to flex across the fastener in a flat open format used for drying.
All pamphlet-style volumes dried acceptably, though the dehumidification samples show the greatest distortion. The patented vacuum-freeze dried sample is thought to have suffered from the size limitations of the compression plates, or its placement next to smaller volumes and folders within a box.
We surmise that the heat used in the patented vacuum freeze-dry process is sufficient to accelerate the movement of the binder's vinyl plasticizers, causing toner from the adjacent photocopies to fuse to the vinyl. Photocopies inserted into the cover's clear vinyl pocket and in contact with the title page blocked to the vinyl and transferred its text to the binder. Photocopied pages within the binder did not, however, block at all.
Because plastic film retards drying, shrink-wrapping needs to be removed from bound volumes for drying by all methods except vacuum freeze-drying. Mold growth resulted before the volume dried.
Coated paper magazines were dried using the same methods as other materials. In almost all instances, coated paper sheets left in direct contact with one another during the drying process adhered. Only vacuum freeze-dried materials were successfully recovered without interleaving. Once an item is blocked, it is seldom separated without incurring damage. Only coated papers dried by vacuum freeze-drying process did not adhere, even though their pages were in direct contact with one another during the drying process.
Rolled items present special challenges because there is often little space available to unroll long items for drying. While efforts have been made to re-house many rolled materials flat or around rigid wide-diameter cores, many rolled items remain unsupported. Curious to see how well rolled items could dry in their existing format, we subjected them to the same methods as volumes and documents. Depending on the length and thickness of paper, most rolled items in our study successfully dried within their rolled formats.
It is not possible to know if the creases and physical damage seen in the patented freeze-dry process resulted from the process itself, or from the thawing and shipment of the items. Though the equipment used to compress materials into shape by the patented process may be ultimately inappropriate for unique archival holdings of disparate sizes or formats, we believe that the process holds great promise for published uniformly bound structures in circulating collections.
Non-water soluble coatings, such as cellulose nitrate, frequently found on mid to late 20th century architectural linens bubbled and delaminated in areas where water was trapped under the film. Damage was apparent in all test samples but seemed to be exacerbated in vacuum processes freeze-drying processes.
Groupings of polyester-sleeved items were placed within sample boxes for wetting and drying to see if they could be successfully vacuum-dried. Would the vacuum process sublimate water out of openings of the sleeves? Would water be effectively removed from encapsulation where corners were clipped? Would water be removed from an ultrasonic or heat welded item?
Vacuum freeze-dried sleeved and encapsulated records dried successfully within their sleeves. A moisture meter reading was slightly below the "dry" range (5-7%). Large quantities of water damaged collections that are sleeved or encapsulated may therefore be effectively vacuum freeze-dried.
Wet or damp sheets left within the sleeves did not dry at the same rate as the non-sleeved records. All of the records set out to air dry did so within 48 hours. Yet a reading taken of a polyester-sleeved sheet after the same period of time showed moisture content of 14.5%. We note that paper needs to be removed from its sleeve to dry.
Most metal fasteners showed signs of corrosion in the short period of time in which they had been exposed to water. Staples, paper clips, and other metal fasteners all exhibited rust. Items that were air-dried or vacuum freeze-dried displayed the least amount of corrosion.