When Preservation Suffers
There can be such enthusiasm in the moment of discovery that it is possible to forget the responsibility to preserve the artifacts that evoke such excitement. For persons working in archeology this may translate into site reports, technical drawings, photography, and many other methods to record the data acquired through excavation. It is also important to preserve the physical integrity of the artifacts once they have been recovered. Many material types degrade rapidly following their removal from the excavation environment where they found the equilibrium that allowed them to survive for so long. Wood loses moisture causing cells to collapse resulting in cracking and shrinkage. Wet organic materials are susceptible to mold and bacterial growth that can be hazardous to both the artifact and the people handling the artifacts. Glass forms caustic pockets along the surface turning it opaque or iridescent. Leather collagen crosslinks becoming hard and brittle. Metals exposed to oxygen begin new corrosion cycles.
In 2003, a cannon was recovered from Fells Point in Baltimore’s harbor (Figure 1). Not considering the need for conservation, the iron was allowed to dry, which caused soluble salts to crystalize and corrosion to occur below the object’s surface. As a result, large plates of iron spall detached from the body of the cannon which removed much of the object’s original surface including markings which may have recorded foundry identification, year of manufacture, weight, etc. (Figures 2-5). These are all unique diagnostic elements, which have been lost due to uninformed decisions made upon excavation.
Figure 1. Mostly intact cannon shortly after excavation.
Figure 2. Spall forming prior to conservation.
Figure 3. Cannon after conservation showing surface loss.
The chemistry taking place as these sensitive archeological materials degrade is complex and varied, and the damage that can occur if the appropriate measures are not taken is irreversible. Archeological conservators are trained to identify the causes of deterioration and determine the best course for preservation. Conservators can provide training to excavators in the safest ways to lift, pack, and store artifacts to prevent damage and optimize the future potential for research and preservation.
When embarking upon the excavation of historic materials it is important to assess both the need for the demolition of a site and one’s ability to responsibly care for the materials recovered. Will the excavation do more or less to preserve the information and materials of the site? Are there resources in place, financial and professional, to manage their conservation? If the answers are yes and conservation advice is needed, contact your State Historic Preservation Office or the American Institute for Conservation, www.culturalheritage.org, to provide contact information for qualified professionals in your region.
Figure 4. Damage to cannon markings.
Figure 5. Repaired fragment of iron spall including cannon markings.