[NHCOLL-L:2508] Re: freezing mounted specimens

[Victoria Book]

Congratulations on your new facilities.

You make several good points, and have good suspicions about freezing.
Freezing is usually *not* the best option for mounted specimens.  Not only
is freezing bad for leather items, but also for bone, ivory, teeth and all
items that are composed of more than one material (e.g. skin and cartilage,
mounts on wood).  As the materials freeze, they often shrink (think mercury
or alcohol in a thermometer) or expand (imagine ice) very slightly.
Different materials freeze and shrink at different rates, and this will
cause the materials to split, stretch, loosen and do other things you don't
want them to do.

Why is carbon dioxide too dangerous?  Unlike fumigants it leaves no residue,
it can be inexpensive, it is not an introduction of anything additional
(hey, we exhale CO2), we drink it beverages...

If you can contain the carbon dioxide in a small tent or bubble, and can
allow sufficient time for it to dissipate into the atmosphere, there should
be no problem.  

I encourage you to continue to explore carbon dioxide and other anoxic
methods before resorting to mass freezing.  There are several resources and
options available to museums.  I can recommend some to you if have
difficulty finding information.

Victoria Book
Conservator
Sam Noble Oklahoma Museum of Natural History
University of Oklahoma
2401 Chautauqua Avenue
Norman, Oklahoma   73072-7029
phone 405.325.5163
fax 405.325.7699
vbook at ou.edu
www.snomnh.ou.edu



On 1/3/05 6:46 PM, "Kathryn Medlock" <kathryn.medlock at tmag.tas.gov.au>
wrote:

> We are currently in the process of moving our entire zoology
> collections to new and better storage and of course wish to ensure
> that pest problems are not just transferred. I might say that we have
> few problems at present and have treated things as the need arises -
> usually be freezing.
> 
> My problem now how to ensure the best way to de bug items prior to
> the move. The collection contains a lot of recent material but also
> includes valuable 19th century mounts of birds (cased and uncased),
> mammals, trophy heads as well as osteological material across a range
> of species. I have been attempting to find out what the best way to
> go will be.
> 
> I am very suspicious of just freezing everything given that it seems
> to be agreed in conservation circles that leather shouldn't be
> frozen. As you would be aware, mounts are made of a wide variety of
> materials - stuffing (straw, wood wool, fibreglass), wire or rode
> metal supports, possibly plaster of paris, glass eyes, wooden base
> that may contain dried vegetation etc etc. What happens to the bills
> of large birds, ivory, teeth, webbed feet etc? Surely these materials
> all react in different ways to the freezing process.
>
> I have been told by some that freezing in OK, by others that teeth
> cannot be frozen. Bromide apparently fades feathers. Carbon dioxide
> is too dangerous and we are not set up for nitrogen.
> 
> Does anyone have any suggestions as to the best way to go. I am in
> favour of treating only if suspicious rather than a blanket treatment
> that may result in damage to the material.
> 
> Sincerely,
> 
> Kathryn Medlock
> Curator
> Vertebrate Zoology, Tasmanian Museum and Art Gallery
>