Freezing botanical specimens

Vicky Purewal <vicky.purewal [at] nmgw__ac__uk> writes

>Dee Stubbs <dstubbs [at] nb__aibn__com> writes
>
>>...
>>Our normal procedure for incoming material is to seal the artifact
>>or specimen in an airtight bag, freeze for one week, defrost in the
>>unopened bag for several days and then refreeze for a second week. ...
>
>The National Museums and Galleries of Wales have been freezing
>specimens for decades and have found no adverse affects. The NMGW
>collection are mounted by gelatine backed linen tape and this is an
>important consideration when freezing as some specimens that have
>been glued can be damaged through repeat procedures and delicate
>flowers have been seen to split and break. If the bags are sealed
>properly before freezing then the RH fluctuations will be greatly
>reduced, but there will still be some stress between the mount
>sheet, the specimen and the method of securing that specimen.

In the freezing process recommended, the moisture content of
specimens in the sealed clear polyethylene bag will increase
slightly due to the reduced temperature and the change in holding
capacity of the air in the sealed bag. This may reduce slightly the
stress of the previous drying of the specimens, not enhance
brittleness. The breakage you observed is most probably due to the
handling of such delicate specimens--as dried flowers. A problem may
occur with specimen sheets  in which an acrylic glue has been used.
The adhesive may became tackier and cause the specimen sheets to
slightly stick together. There is a great range of tackiness of
acrylic adhesives, its a matter of checking with the manufacturer
and obtaining one with low tack and works for you.

Mary-Lou Florian
Conservation Scientist
Research Associate Royal British Columbia Museum.


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                  Conservation DistList Instance 18:38
                Distributed: Thursday, February 10, 2005
                       Message Id: cdl-18-38-004
                                  ***