BIRD MUMMY CONSERVATION - A DELICATE BALANCE
By Alison Whyte, Conservator at the Oriental Institute Museum
The Oriental Institute Museum
The University of Chicago
(This article originally appeared in The Oriental Institute News and Notes, No. 214, Summer 2012)
CONSERVATION CONCERNS: ORGANIC MATERIALS
The project to CT scan the bird mummies, while of great interest to the Conservation Department, also caused some apprehension. A cross-campus trip to the University of Chicago Medical Center could be damaging for any object in the collection but was of special concern for the bird mummies. Mummified remains, both human and animal, are among the most fragile archaeological objects in our collection. This is because, as organic materials, they were once living things. During their lifetime, their tissues would have contained water, and now, as non-living objects, they are desiccated, fragile, and particularly susceptible to fluctuations in relative humidity (the water content in the air).
When the relative humidity changes, it leads to dimensional changes in objects made from organic materials. If the relative humidity rises, the object absorbs water and the material swells. When the relative humidity drops, the water is released, and shrinkage may occur. This kind of dimensional change will lead to physical damage in a mummy particularly if there are cycling fluctuations where the object is repeatedly shrinking and swelling. Since relative humidity and temperature are linked, the control of both of these environmental conditions becomes of paramount importance. The Oriental Institute Museum's climate-control system makes this control possible; however, a trip outside the building and to the hospital could mean drastic changes in environmental conditions.
Conservation concerns for mummified materials are further complicated by another issue. Mummified remains are often made up of more than one type of material. For example, in addition to the body, there may be linen wrappings and/or a wooden coffin encasing the body. Each of these materials is organic in nature and therefore just as susceptible to fluctuations in relative humidity.
PACKING & TRANSPORT:
When transporting objects outside the museum, one always hopes for weather that approximates the environmental conditions we specify for the objects in the museum so that fluctuations are minimized. For organic materials, this means 65 degrees Fahrenheit (+/- 5 degrees) and 45% relative humidity (+/- 2%). A mild, clear day with no rain would be optimal; however, we also have to be flexible since the first priority for the radiologists and the CT scanner must obviously be their living patients!
In addition to concerns about damage from environmental fluctuations, the potential for damage from simple movement had to be addressed. Since each bird mummy varies in size, condition, and composition (i.e., presence or absence of linen wrappings and/or wooden coffins), a custom packing system was devised for each one. This system was composed of a custom-built box made from acid-free board and twill tape and one or more of the following cushioning materials: acid-free tissue, museum-quality packing foams, and polyester batting lined with washed Tyvek (a high-density polyethylene fabric). Often the packing system required a delicate balance. On the one hand, enough support was required to prevent the bird mummy from moving around too much during transport. On the other hand, if the bird mummy was packed too tightly, the delicate wrappings and/or feathers could be crushed. See figures 2 and 6 for images of the bird mummies in their boxes.
Revised: September 11, 2012