Exhibit cases

Diana Banning <dbanning [at] ci__portland__or__us> writes

>An exhibit case is being designed for our new facility and I am
>searching for an appropriate material to use for the back of the
>case.  This back board, for want of a better term, will be used to
>tack items to as part of the exhibit(s).
>
>A brief description of the case:
> ...
>    Interior climate will echo the stacks (63 deg F, 40% RH) with, I
>    am told, a pretty constant air exchange.

There is likely no need to encourage air exchange between the
interior and the exterior of the display case. Most cases leak just
fine as built--it's sealing them to prevent air leakage that is the
challenge. If the stacks surrounding the case are kept at the
desired conditions for the environment in the interior of the case;
if the case is not "super-sealed"); and if display lighting does not
have an appreciable effect on the temperature of the case, then
there will likely be adequate interior/exterior air exchange to
maintain a microclimate at an appropriate temperature and humidity.
Too much leakage will encourage dust collection.

However, if the build up of off-gassing from case materials or
artefacts is a concern, you might wish to ensure that there is
adequate air exchange to prevent the build up of these pollutants.
To determine how leaky the case should be, I would suggest
consulting "Airborne Pollutants in Museums, Galleries and Archives"
by Jean Tetreault of the Canadian Conservation Institute. The good
news is that in my experience most cases will leak more than enough
(without encouragement) if the case's pollutant load is mitigated by
careful choice of materials (which is Ms Banning's original
concern).

>Are there any materials you could suggest that would a) be
>acceptable in an exhibit case, b) be durable to many year's exhibits
>and wouldn't crumble after having things poked into it repeatedly,
>and c) can be easily be found in sheets large enough for the case?

Ethafoam or some other brand of polyethylene foam (there are many)
might prove adequate. Note that these materials are available in
various densities, and that a heavier density board will be more
rigid and longer lasting. The foam is available in large sheets, and
can be easily cut (These foams used to be produced in 2 x 4 x 10
foot "loaves", and then cut to 4 x 10 foot sheets, I doubt this has
changed). By using a relatively thick sheet of foam, and some long
and slim pins (such as dressmaker's T pins), a sheet of foam should
be adequate for many exhibitions.

Jerry Shiner
Keepsafe Microclimate Systems


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                  Conservation DistList Instance 22:24
                 Distributed: Monday, October 20, 2008
                       Message Id: cdl-22-24-003
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