by Paul Storch
In this article I can only give a brief introduction to the conservation of artifact materials from freshwater archaeological sites. I say “freshwater” rather than “underwater,” because there are significant differences between conservation of objects from a marine, or salt water, environment, and conservation of objects from a freshwater environment, such as Lake Superior and most Minnesota rivers. Treatments developed for marine sites may be unnecessary and uneconomical at best, and do irreversible damage at worst.
The field of archaeological conservation is evolving rapidly from its roots in classical restoration and chemistry into a specialized applied science; we need further development of methods specifically suited to freshwater sites and information exchange at conferences such as the shipwrecks conference.
Under the Water
The major types of materials found on most Great Lakes shipwrecks from the 19th through the late 20th centuries include inorganic (e.g. iron and brass) and organic materials. Most organic objects are made of wood, but often other organics, such as leather, and textile fibers, such as wool and cotton, are preserved.
The key concept to remember with archaeological materials, whether they are buried in the ground, submerged in the water, or buried in submerged sediments, is that these objects have equilibrated with their burial conditions. That is, deterioration has progressed to a certain point and then stopped, or the rate has drastically slowed down.
Well pulley from Fort Snelling, ca 1820-30s; wrought iron is in direct contact with wood. The iron is heavily corroded and the wood is swelled. It is not possible to dismantle objects such as this to attempt to treat the components differently without destroying the object and its integrit
If the equilibrium conditions are maintained in the burial environment, then the materials will remain in a state of preservation. If something happens to disturb the equilibrium— such as archaeological excavation or a natural change, like a drastic drop in waterlevel—the materials will begin to reach equilibrium with the new conditions. This results in renewed deterioration, which in the case of metals can mean the formation of additional oxides, and for wood the loss of water and resultant shrinkage and cracking.
The logical extension of this concept in practical terms is that one must be prepared—with the proper methods and supplies—to re-create as closely as possible the equilibrium after excavation and removal from the burial environment. Failure to do this is the antithesis of ethical conservation practice, and inevitably leads to the loss of information at the least, and total loss of the object at the most.
Chemical considerations will have to wait for another post...
by Paul Storch