Vacuum freeze drying is the safest and most successful method for books, although it is also the most expensive. Materials must be frozen when

they are placed in a sublimation chamber. This type of chamber operates under high vacuum and high heat, and turns the ice crystals in and on

the frozen materials to water vapor. The vapor is then collected on a cold panel that has been chilled to at least -200 degrees F, so it

cannot go back on the materials. If they are not frozen when they are put in the chamber, the materials will freeze on the outside and the

water molecules on the inside will be forced through the frozen barrier as the vacuum is pulled. This action can cause the book or document to "explode."

 

Vacuum freeze drying is a last resort drying method for very large numbers of photographs and can not be applied to all processes.

Sticking of emulsions has sometimes been observed with freeze drying.

 

When materials are removed from the vacuum freeze chamber, they will be very dry and should acclimate for at least one month before they are

opened to avoid cracking the spine and/or binding (this is especially true for leather bindings). They may be placed in a high humidity room

to accelerate the acclimation process, but must be monitored closely for signs of mold.

 

Materials so treated will not look like new, but will show signs of swelling and distortion. Stanford University Library staff members

reported they needed an additional twelve percent of shelf space for materials that had been treated in Lockheed's chamber. Photographs will

not be damaged by this treatment, but rubber cement may dissolve and stain the pages to which it has been applied.

 

 

 

Vacuum drying involves the placement of wet materials in a chamber that pulls the moisture out by means of a vacuum. This

method is not recommended as the heat involved is damaging to paper (especially bound paper) and photographic materials.

Microwave ovens should not be used for the same reason.

 

Vacuum thermal drying is not recommended for any type of photographic material as it will cause photographs to stick

together in a solid block.