Document Freeze Drying Process
Firstly, the documents are frozen solid in order to maintain their structural form. Next, they are placed in the freeze drying chamber and a high-pressure vacuum is applied to remove any air. When the correct pressure and temperature are achieved, the moisture is converted to vapour. This collects on a condensing surface outside the chamber (typically colder than 40ºC/-40ºF), and turns it back to ice. Finally, a gradual temperature rise completes the process by driving off more vapours and eliminating bound water from the documents.
Freeze drying can typically restore the following documents:
- Books and manuscripts: coated papers, leather, maps, parchment, pulp paper, vellum, drafting linens, text books, reference books, manuals
- Business records and documents: legal files, patient and medical records, x-rays, engineering and architectural plans and drawings, catalogues, reference materials, certificates, contracts, passports, transcripts
- Historical and collectible items: archival documents, rare documents, maps, stamp collections, money collections
- Keepsakes: photographs, leather and hide items, newspaper articles, recipe books, cards, scrapbooks
- Textiles: embroidery and needlework, silks, tapestries
- Artwork: acrylic paintings, linen drawings, water colours
Freeze drying offers a practical and effective solution for water restoration, but the restoration quality depends on the material being freeze dried. Documents made of a variety of materials with different absorption properties may become deformed as expansion occurs at a non-uniform rate. Water can also cause mould to grow or make inks bleed, in which case, freeze drying may not be an effective method for document restoration.
Cuddon Document Freeze Drying Videos
See document freeze drying in action using Cuddon Document Freeze Dryers:
- NZ National Library Video: Freeze drying to restore documents
Cuddon produces document freeze drying machines for sale worldwide.