Vacuum drying books

In response to Michael Rhode's request for suggestions, I would like to
share a experience in vacuum freeze drying, being struck at the time by
the general recommendation of this method of conserving water-damaged
material, and the dearth of technical information in support thereof.

The unit operated by the South African Medical Research Council was
large enough to accommodate a single volume, and while already frozen to
-18 degrees Celcius by refrigeration, the solid block was immersed in
liquid nitrogen, with a temperature of -196 degrees Celcius, to ensure a
solid state and direct sublimation to the vapour state, to avoid the
surface distortion effects of liquid water. The weight of the volume was
used as a control to determine the duration of the cycle, and after 72
hours at -70 degrees Celcius and 100 millitor vacuum pressure, the
decreasing weight was noted to level off.

My personal estimation is that at that point the paper had become
desiccated, a slight cockling was noted and the glued spine was also
slightly concave, compensated by a short period of equilibration in our
ambient subtropical climate. Three years later the volume is still in
circulation, so the operation must be rated a success, but any specific
recommendations on this procedure would be useful.

Dale Peters
Paper Conservator
Campbell Collections of the University of Natal
220 Marriott Road, Durban, 4001
South Africa

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                  Conservation DistList Instance 8:20
               Distributed: Wednesday, September 21, 1994
                        Message Id: cdl-8-20-003
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