Jen Jackson 2/9/09
Good morning Mounties- I have a question about case conditioning... My museum is adding a new wing with about 30 new artifact cases. The case company has assured us that we will have desiccant chambers in all of the cases, so that we can use conditioned silica to control our case environments. This seems like a wise strategy in all but a few cases. About three of our cases are so large (17'7" W X 8'H X 3' Deep) that it seems like we would need a snow shovel to fill the desiccant chambers. The company (Meyvaert) has suggested active case conditioning- however I am only familiar with positive pressure case conditioning- which I understand is primarily for dust mitigation. Our Exhibit hall is temperature controlled, but not humidity controlled. Do you guys know what the benefit of active case conditioning would be in these cases? It is vastly more expensive, and I just don’t know if it is worth it. Any info would help.
Thanks guys- JJJ
Dave 2/11/09
Good Morning Jen,
I forwarded your question to one of our conservators, Jeff Maish and
this was his response:
This is a good question since this is a huge case, roughly 360 cubic
feet. A lot depends on
a. how well sealed the case is
b. what the gallery environment is
c. what the RH is in the case. (target RH)
If the case is not really well sealed and the gallery is uncontrolled
passive gels are not going to work and you might have to go with what's
called a micro-climate generator. This is a somewhat standard approach
with large cases, especially since air has to distribute through such a
large volume.
If everything is well sealed, the gallery is stable at 50%, and you're
trying to maintain 40% in the case, a series of ArtSorb or Arten
casettes might work. If I recall correctly one ArtSorb casette can
control 32 cubic feet of air space, so in theory 12 of these could
control the case. I would try more, and also distribute them around the
case. Gallery conditions and case construction would have to excellent
though. Arten and Artsorb also have a higher moisture capacity, so you
don't have to use as much as silica gel. It becomes an issue of air
exchange with the gel in such a large case though.
Hope this helps.
Dave
Jen Jackson 2/12/09
Dave (and Jeff),
Wow! That is incredibly helpful information. I had previously been
referring to an old data sheet that recommended .5 -1kg of Artsorb per
cubic meter of airspace, and then converting from feet to meters. I
also did a little research on micro-climate generators, and was able
to find the company that is selling the machine to the company that is
trying to sell the machine to us. It seems like the micro-climate
generators could really save quite a bit of maintenance over the life
of the Gallery. I really appreciate your help! Thanks so much- JJJ
PS- I read that the standard we should shoot for is 50 percent RH (+/- five percent) and 70 degrees Fahrenheit- these large cases are filled with weapons from the early 19th century, some even the 18th C.- anybody out there have any suggestions for RH given the combination of steel & wood?