Hi Marielle;
The process we follow is to clean and bag the item (sometimes wrapped
in A/F tissue, sometimes not), freeze it down to -28 C (about -14 F, I
think) for AT LEAST 48 hours--that's 48 hours AT -28 C, not 48 hours
from the time the piece goes in the freezer until the time it comes out
(I usually allow an extra day for the piece to cool down to -28). We
don't unwrap and clean the piece when it comes out of the freezer--we
leave it sealed, let it come to room temp for 48 hours, then back in the
freezer to be at -28 C for another 48 hours. This second freezing is
essential, as some bugs can adequately prepare themselves to withstand
even that temperature, but can't thaw themselves and then quickly
prepare themselves for another freezing. The amount of time at room
temp. is the most important one--I've left things in the freezer for
longer than needed (just as my schedule works out), but if the piece is
at room temp. too short a time, any bugs that got through the first
freezing may still be in deep-cold hibernation; if left out too long,
they may have had enough time to recover from the initial cold shock to
prepare themselves to withstand the second cold shock as well.
We looked into renting a freezer truck to do some over-sized items that
won't fit in our chest freezer--we found that the trucks don't get cold
enough to do the job. The anoxic treatment seems to be getting more
popular--I had several suggestions for that a month or two back when I
was looking for input on treating large artefacts. Strikes me as a
safer option for your collections, as you're not putting them through
the radical temp/RH changes that come with freezing for insects.
Cheers
------------------------------------------------------------
Tim McShane, Assistant--Cultural History
Medicine Hat Museum and Art Gallery
1302 Bomford Crescent S.W.
Medicine Hat, AB T1A 5E6
Tel: (403) 502-8587
[log in to unmask]
>>> [log in to unmask] 05/12/05 7:05 AM >>>
Good morning!
I am wondering what everyone's opinion is on freezing treatments for
dermestids. The objects themselves are not the issue today, but what
length
of time to freeze. When I was an intern at a museum we froze infested
items
after a good vacuuming, wrapped in acid free tissue, bagged and sealed,
we
would freeze the items for a two week period. Remove and gradually thaw
to
room temp then clean again, bag and seal for one more two week period.
I've
caught wind of the new idea that 48 hours in -20 F would be all that
was
needed. For me the jury is still out on such a short treatment. Also
are
there better options than freezing? We have also thought of oxygen
deprivation chambers. I welcome everyone's opinion.
To give some history my infestation is of dermestids (pesky brats that
I've
been lucky enough to find live and dead!) They are everywhere but we
are
mostly concerned with our vast uniform collection. What also would be
the
most convenient way in time and money to treat over 200 items.
We will be moving to a new building in about a year and I don't want
the
infestation to follow. But I also don't want the next 5 years of my job
to
be spent freezing, thawing and cleaning this enormous collection. We
have
thought of renting a refrigerated truck, has anyone tried this method?
Thank you all for advice in advance. I really enjoy the discussions on
this
board.
From the Dermestid Queen of the east coast!!!!
Marielle
**********************
Marielle Fortier
Registrar
Norwich University Museum
Northfield, Vermont 05663
**********************
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