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?