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6. Vacuum freeze-drying vs vacuum-drying

Conservators are often asked which of the two is the preferred method of drying wetted documents and books. At the moment there are no set answers based on standards derived from usage. And much depends on the circumstances. However, in general terms, freeze-drying appears to be the preferred method for wet books. Stabilization is immediate, the stresses a bound book would suffer are minimized, books of coated stock do not stick on drying, soluble colors and inks, fillers and adhesives stay in place.

On the other hand, vacuum-drying is a wet process. Pre-freezing is not involved, it is somewhat more economical than freeze-drying, the moisture is removed by evaporation. It is widely used for wetted records. However, the advantages of stabilization are lost where danger of fungal attack exists or soluble elements are present. In this connection, Plink (18) wee faced with the dilemma of drying the rare mid-nineteenth century Kleineschmidt manuscripts which were in a frozen state. Preliminary tests indicated that soluble inks and colors might feather or run with vacuum-drying. So he selected freeze-drying, by-passed the liquid phase during the drying cycle, and ended with successful results.


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