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Subject: Freeze-drying

Freeze-drying

From: David A. Tremain <david_tremain>
Date: Friday, April 4, 2003
Alan M. Farancz <farancz-conservart [at] att__net>

>I am acting as a consultant for the rescue and recovery of some 5000
>plus documents at a site at ground zero, September 11, 2001. The
>records for these documents are no longer available, the documents
>were wet and there was a severe mold infestation as well as diesel
>fuel in the water.  Examination could not be done until the site at
>ground zero was cleared and the structure stabilized. The water line
>is about 4 feet off the floor. The documents are in file cabinets,
>on rolling stacks and some are bundled in plastic. The documents by
>and large are still wet from the 9/11 event until today
>
>I am interested in getting information from book and paper
>conservators who have worked on items that have printed colored inks
>on the pages of the documents and in the books after they have been
>freeze-dried.  After freeze drying was it possible to easily
>separate the pages? Could the pages be separated without lifting the
>ink? Do some inks break down from the freeze-drying process?
>
>The interest here is to preserve the information on the document not
>the documents themselves. I would also like to hear the pros and
>cons of the freeze-drying process

I presume these documents will be vacuum freeze-dried, not vacuum
thermal dried, which can make a difference to the stability of inks
and dyes. During the  liquid phase of vacuum thermal drying if any
of the inks are water-soluble, any contact with water will cause
them to "bleed".  I have not seen printed inks "break down", and I'm
not sure what is meant by this. Flaking or powdering maybe? There
could be some print off-set onto the plastic,  which should be
removed prior to freeze-drying as this will slow down the drying
process. However, if the documents have already been frozen this may
not be possible.  In my experience it should be possible to
separate the pages after drying provided they are not printed on
coated paper which has already stuck together. In which case, if the
paper has been allowed to dry out before salvage, which I suspect
may have been the case at Ground Zero, given the temperatures at the
time and the length of time before the documents could be salvaged
(hence the mold ), it may not be possible to separate them.

Much of the diesel fuel in the water will be extracted during the
freeze-drying process and be part of the ice that forms in the
condenser. I know this from air crash documents we have freeze-dried
at CCI where documents have been soaked in aviation fuel. However,
there may still be some odor.

Since the documents are moldy, freeze-drying them (usually at around
-25 deg. Celsius or colder) is sufficient to "kill" the mold, or at
least render it dormant. The documents can then be cleaned and the
mold brushed off after drying.  They can then be photocopied or
microfilmed.  A photocopier dedicated solely for these documents
should be used, then discarded afterwards.

The main concerns with freeze-drying tend to be cost and whether to
use heat.  If these are corporate records where there is no historic
or cultural value to them, vacuum thermal drying can be used, and
tends to be cheaper than vacuum freeze-drying because heat is used
during the drying process and takes less time.  I know some
companies charge according to how many cubic feet are being dried,
while others may charge in hours. However, the problems associated
with vacuum thermal drying have already been outlined above.  If
they have archival value, then vacuum freeze-drying should be used,
where no heat is involved (the water in the form of ice passes
directly from the solid phase to the gaseous (vapor) phase by a
process of sublimation). Be aware that while some companies claim to
use vacuum freeze-drying, some in fact still use heat, so you need
to be persistent with them, question them in detail, and if
possible, visit their facilities. Check also to see whether they
have treated historic or cultural property before. The likelihood is
yes, given so many floods in libraries and archives, but it is as
well to check. Hope this helps,

David Tremain
Conservator / Restaurateur
Preventive Conservation Services /
Services de conservation preventive
Canadian Conservation Institute / Institut canadien de conservation
613-998-3721
Fax: 613-998-4721


                                  ***
                  Conservation DistList Instance 16:59
                   Distributed: Monday, April 7, 2003
                       Message Id: cdl-16-59-002
                                  ***
Received on Friday, 4 April, 2003

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