Controlling the relative humidity to the standards required by conservation for the protection of moisture-sensitive objects is difficult for most museums to achieve. It is virtually impossible for museums housed in old buildings, such as Field Museum an expansive central hall stretching the entire length and height of the building with equally large exhibition halls opening off of this main hall.
Faced with several major reinstallation projects, all of which include large quantities of moisture-sensitive objects, Field Museum has chosen a new approach to the relative humidity problem; to control only that space with which we are concerned, that is, the space immediately surrounding the objects.
Two years ago, we took designs for a relative humidity module developed at the Canadian Conservation Institute, modified them and built a machine to control two exhibit cases. We further modified the machine a year ago so that steam rather than evaporation now produces the humidity. This machine provides an efficient, low-cost means of controlling the environment within an enclosed space. One module is able to control more than one case, with a capacity of controlling up to 3500 cubic feet.
The module will be described as well as the means by which cases are connected to the module and linked to each other. The different configurations of linked-up cases now in use at Field Museum will also be described. An evaluation of the module will be discussed on the basis of one machine that has been in use for over 2 years and three machines for over a year.