Conservation will shortly be starting a multi-year project to address salt contamination in its Central and South American Archaeological Ceramics. A condition survey identified those ceramics exhibiting deterioration from soluble salts. Stabilization will be achieved through the removal of the salts.
The Field Museum holds outstanding collections of well documented archaeological ceramics. Those from the Southern Andes for example, are a primary research resource for anthropologists, human biologists, and archaeologists. The 1925 and 1926 collections from Peru by noted anthropologist Alfred Kroeber are some of the most important in the world due to the excellent scientific context and state of preservation. The Kroeber collection from the Lima and Canete Valleys represents important material of the Lima, Wari, and Inca cultures. They shed light on the Lima culture, a little known but important part of Andean prehistory contemporary with the Ancient Nazca, and are a key collection for understanding the relationship between local groups and imperial colonizers during the Wari and Inca periods. Other important southern Andean ceramic collections include the G. A. Dorsey collection from Ancon, scientifically excavated in 1891, documenting late Wari, late Intermediate, and Inca presence on Peru’s central coast.
Contamination with water soluble ground salts, especially chloride salts, is common to archaeological materials. With fluctuations in relative humidity, these salts crystallize and rehydrate near the surface of the ceramic, causing the surface to breakup and powder or flake off. The ceramic is weakened and critical surface detail is lost. Eventually the ceramic can be lost entirely. The preservation of surface detail and ceramic body is critical to their research value, making the stabilization of these ceramics a high conservation priority for the department.
To determine the extent of the problem of salt damage, conservation recently completed a condition survey of all 15,000 ceramics in the Central and South America archaeological collections. The survey identified those ceramics, representing 23% of the collection, that exhibit deterioration from soluble salts.
The least interventive approach to addressing the problem is to store and display objects in an environment with an extremely stable relative humidity to minimize the dehydration and hydration of the salts. For structural and equipment reasons, this is not possible in the collections storeroom available in the Museum. We have successfully used microclimate enclosures for archaeological metal objects and a few large pieces of salt contaminated stucco with iron armatures; however the number and size of the unstable ceramics and the degree of access required of the collection makes microclimate enclosures unfeasible.
Stabilization will instead be achieved through the removal of the salts. Objects will be treated through a series of immersion baths in deionized water until conductivity readings indicate that no more salts are migrating into the soak bath. Severely damaged surfaces will require consolidation prior to wetting and soaking. Those that are friable or lightly flaking will be consolidated in the laboratory with an acrylic polymer resin (Acryloid B-72) applied locally or by immersion, depending on the severity and/or extent of the damage. Some ceramics are flaking so severely that they can not be moved from their storage shelf without significant loss of material. These ceramics will be consolidated in situ with molten cyclododecane wax, then moved to the laboratory for documentation and desalination. Treatment will ensure that these important objects are available to researches in future.