Stuffed specimen and hygrometry

Gerard Cobut <gerard.cobut [at] naturalsciences__be> writes

>In the Natural Sciences Museum (Brussels) I am currently facing a
>conservation issue. Relative humidity is decreasing steadily in one
>showcase; the conditions in it are now really too dry.
>...
>The showcase has 2 Art Sorb cassettes in its right wall; the holes
>through the wall (between the cassette container and the showcase)
>were made according top the Art Sorb instructions manual.
>...
>... Mean hygrometry is
>steadily decreasing (+/- 45% relative humidity on November 18, less
>than 35% on December 4, 2008).
>
>Has anyone experienced something similar? Is the instrument we use
>known to be reliable? What is the Art Sorb's behavior? Is it
>possible that it would absorb "avidly"? Can the stuffed specimen be
>highly hygroscopic (absorbing humidity from the atmosphere)?

A few things come to mind:

Verify that the ArtSorb is conditioned to the required RH and hasn't
been allowed to dry further than the target RH.  These cassettes
should be unwrapped just before use.

Compare the RH behind the right wall with the RH in the case.  If
the RH behind the wall is correct, there is a slow humidity transfer
and the stuffing in the animal might play a  short term role in the
exchange.

The location you are reading with the Hanwell may not representative
of the case.  This doesn't seem likely since the case temperature is
within range, i.e. its not warmer than elsewhere in the case. Its a
good size case so the animal stuffing could play a short term role
in the immediate environment (if it was desiccated), but I would
think the RH would stabilize after a few weeks.

Confirm the holes sizes in the wall are adequate and also not
covered with anything that could be a moisture barrier. Hope this
helps,

Jeffrey Maish
Associate Conservator of Antiquities
The J. Paul Getty Museum
1200 Getty Center Dr. Suite 1000
Los Angeles CA 90049-1687


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                  Conservation DistList Instance 22:36
                 Distributed: Monday, December 15, 2008
                       Message Id: cdl-22-36-003
                                  ***