- THE MAGAZINE
The freeze-drying method was first tested and used in 1890 in Leipzig, Germany. The U.S. government used it as a means to store human plasma during World War II. By the 1950s, the process of freeze-drying was routinely used in the food and drug industries. And by the 70s, restorers began using it as a way to recover water-damaged books and documents.
The process removes water from documents, keepsakes and other items after they are frozen, allowing them to maintain their shape and biological structure. Objects are first frozen solid in order to lock the structural form firmly into place (objects will maintain their pre-frozen shape throughout the entire process).
Next, objects are placed in the freeze-drying chamber and a vacuum is established, which ensures that the chamber is devoid of air and operating at a very low absolute pressure. When the inside of the drying chamber reaches the proper pressure and temperature, the moisture in the frozen objects is converted to vapor.
Thirdly, a condensing surface outside the chamber, typically colder than 40ºC (-40ºF), attracts the vapor coming off the frozen object and turns the vapor back to ice. This also protects the high-grade vacuum pump from water, oils, and fats that might be part of the composition of the object being dried. Finally, a controlled gradual temperature rise completes the process by driving off more vapors and promoting the release of bound water from the product. It is interesting to note that 90% of the drying is done at temperatures below freezing.
Freeze-drying is sometimes confused with vacuum drying. While both techniques can remove water and both involve the use of a vacuum, freeze-drying creates a much higher vacuum pressure. Freeze-drying offers several advantages. For example, freezing the water-damaged item immediately stabilizes it and allows it to be stored indefinitely before it is dried. The water in the object remains frozen while the freeze-drying process converts it to a gaseous state. The water does not remain frozen in an object that is vacuum-dried, however. Vacuum drying changes a liquid to a vapor and can result in a much greater risk of expansion, distortion, sticking, and staining. Vacuum drying can allow an item to acquire additional damage because the drying process can take several weeks. During this drying process the water in the item remains in a liquid state until it evaporates. It is because the water in the item stays in a liquid state until it evaporates, that the vacuum drying process allows inks and other substances to move around.
As Alan Anger puts it, “However, there’s another enemy of water-soaked items that is often over looked. This villain is time. The problems associated with water damage – absorption and swelling, mold infection, migration of inks and dyes – all grow worse with the passage of time. The more time that passes, the more complicated, expensive and time consuming it is to salvage an item.”
Anger went on to explain, “Stabilizing an item by freezing it as soon as possible after it’s been damaged dramatically increases the odds that it will be able to be salvaged satisfactorily. Simply placing a water-damaged item in a freezer is an important first step in the freeze-drying process.”
During the Luther Hospital incident, Metro Restoration and Thunder Restoration, two normally competing companies, worked together. Robert A. Laurent of Metro Restoration explained, “We initially got the call that the building (hospital) had been flooded. They had cleaned up a lot of it – the mud, etc., but the adjuster told them that there might be hidden moisture there. When we got there the first day, we found that there was water in the walls and I told the person in the X-ray department that we should get the X-rays frozen as soon as possible. Even if we eventually found that there had not been serious damage to the X-rays, if we froze it right away, that would immediately stop whatever processes it was going through.”
Laurent says he knew almost upon arrival that he was going to need an extra helping hand on this job, “We were initially told that the job would involve us working with about 15,000 sq. ft., but when we arrived that first day, we found that the affected area was more like 80,000 sq. ft. That’s when I called Jason [Jason Hagen of Thunder Restoration]. I knew I would need about 10-16 guys, which ended up taking both of our companies to cover all of the labor and the equipment.”
Laurent and Hagen had worked together previously, and so as Hagen puts it, “Metro (Restoration) had been given the hospital job by an adjuster and then Metro called me to help them out because it was a fairly large job. We were drying the structure of the hospital when they told us that the X-rays were molding. About 11/2 months before, I had purchased two freeze dryers. I bought four more freeze dryers and took all the X-rays and put them in. Because the hospital needed access to the X-rays 24-hours-a-day, we labeled the files so that doctors could just come in and find what they needed at any time. It took us three days, but we re-filed everything back to its original place.”
The job took approximately three months to complete. According to Laurent, they used commercial freezers, about 20 cubic ft., to freeze the X-rays and a large Reefer freezer semi-truck trailer, and then about six freeze dryers from Freeze Dry Specialties Inc. to freeze-dry the X-rays. “It’s a really big job. It is really a matter of trial and error. You do the first batch and you figure out how long it will take to dry. It might take a while, but you shouldn’t take it out too soon. Nothing will happen to the documents — the materials, if you leave it in too long, but it won’t work if you take it out too early,” said Hagen.
When asked what advice he would give restorers who were looking to get started in freeze-drying, Hagen responded, “I would recommend researching the costs, how much you can handle — can you afford not begin paid until you are done with the job? For example, one job we did took three months and we didn’t get paid until we were done. When I first bought a machine, I started freeze-drying right away and was working for six months straight with two machines that featured six chambers each. Then, I didn’t have a job for two weeks. It can be rough.”
Laurent offered this advice: “I would say that you need to find out if you will be getting a steady flow of jobs because once you make that commitment, it can be fairly expensive, and you need to know if you can make a profit soon after starting or have an avenue for getting those kinds of jobs.”
Anger and Terry Smith, V.P. of Water Removal Technologies Inc. (a newly formed division of Freeze Dry Specialties Inc.) have several patents pending for water restoration applications. One of their patent applications was created for deodorizing water or smoke-damaged items during the freeze-drying process. “This type of deodorizing is very new to our industry. Any porous item, such as paper, clothing, or tapestry can absorb odors. Using a freeze-drying vacuum chamber, we create a perfect vacuum and remove all of the air from the item. We then add deodorized air back into the chamber for the pores in the item to absorb. After only an hour in the chamber, the item is completely deodorized at a cellular level,” explained Smith.
Freeze-drying offers restorers a practical and effective solution for water restoration. Not only have the benefits been proven, but new discoveries have expanded its uses. From water restoration to deodorization and preservation, the uses of freeze-drying are more varied than ever. If the idiom whatever we possess becomes of double value when we have the opportunity of sharing it with others is true, then Laurent and Hagen have added double value to the work they did at the Luther Hospital.
Books and Manuscripts: Coated papers; drafting linens; leather; maps; parchment; pulp paper; and vellum.
Business Records/Documents: Attorney client files; company files; confidential records; doctors’ office patient records; plans or blueprints; product catalogs; reference materials; trade secret records; appraisals; birth certificates; contracts; death certificates; household records; loan agreements; passports; school transcripts; securities; maps; and tax records.
Historical and Collectible Items: Badges; baseball cards; certificates; porous board stock boxes; rare documents; and stamp collections paper money collections.
Keepsakes: Baby books; baskets; family collections; leather and rawhide items; newspaper articles; recipe books and cards; and scrapbooks.
Textiles: Embroidery; flags; needlework; silks; and tapestries.
Paintings and Drawings: Acrylics; drafting cloth; linen drawings; and water colors.
Photographs: Albumen prints; aperture cards; chromogenic prints; gelatin dry plate glass plates; matte and glossy collodion prints; photomechanical prints; and prints.