Freezing objects

Ellen Roblee <robleee [at] nmaicrc__si__edu> writes

>...  Could those of
>you who have seen damage caused by freezing for pest control please
>share your observations? The damage we are concerned about includes
>cracking, crack propagation, delamination, fatty bloom, spew (spue
>for some of us), loss of adhesion, exacerbation of bead disease and
>so forth.

During times of serious museum infestations, I have frozen many
objects from a variety of sources including African, Oceanic and
South American, and have never seen visible damage.  However, I have
always taken quite a few precautions to mitigate possible
condensation/dimensional damage.

I always use plenty of acid-free tissue, unbuffered if in contact
with wool or other proteinaceous materials.  I always double bag and
seal both bags tightly to avoid drying out during freezing.

The wrapped objects are put into the cold freezer without stacking
to make sure of a positive kill.  However, I always TURN OFF the
freezer after the treatment period with objects inside and allow the
slow defrosting of the objects  (objects raised off the bottom, of
course).  This seems to cut down on the condensation formation, and
also prevents damage to objects due to warming shock and also being
handled in a very cold and perhaps brittle state.   It also allows
the freezer to be cleaned out each time to prevent frost build up.

After removal from the freezer, I always let objects equilibrate for
at least 24 hours before unsealing, just in case humidity within the
package had changed.

I admit these steps slow things down a great deal, but I have never
seen any condensation or dimensional damage as a result.  Perhaps I
have just been lucky.  I admit I have never frozen "diseased beads",
and no long-term effects study has been done, so I cannot comment on
this.

Linda Roundhill
Art and Antiquities Conservation
Woodinville, WA
425-481-0720


                                  ***
                  Conservation DistList Instance 14:54
                  Distributed: Friday, April 13, 2001
                       Message Id: cdl-14-54-004
                                  ***