Metal Conservation
Elizabeth Kallenbach
Artifact conservation is an important component to lab work; when artifacts are recovered from the field and brought to the lab, they sometimes require careful cleaning and handling, particularly organics such as textiles, leather, shell, and bone tools. In addition, iron, or ferrous metal artifacts, often require cleaning and conservation in order to identify the object, and to stop the corrosion process. The Research Division Archaeology lab uses a method called electrolysis to conserve metal artifacts. Electrolysis is the process of using electricity to convert rust back to iron. Corroded (rusty) artifacts can often be returned to their original condition, or close to their original condition. The artifact is placed in a tub filled with an alkaline electrolyte solution of tap water or de-ionized water and washing soda. The negative charge from a battery charger is attached to the artifact with wire. The positive charge is attached to a piece of scrap metal (this is the iron anode or positive electrode). During the conversion process, eclectically charged ions are released from the artifact, moving through the electrolyte solution to the positively charged pole. During this process, the outer layer of ferric oxide (red rust), is flaked off. A layer of harder, black rust is often underneath. In most cases, this black rust can be converted back to metallic iron through the release of hydrogen. The length of time required to complete the process depends upon the size and condition of the artifact. Larger objects such as iron stove parts and horse shoes can take two to three weeks. Smaller artifacts such as coins, buttons, and nails may take one to three days. After the process is complete, artifacts are washed and treated with tannic acid or sewing machine oil to avoid further rusting. For the Museum's new exhibit, "Oregon, Where Past is Present", a historic military canteen dating to the late 19th Century was treated with the electrolysis bath. The canteen was originally covered with a layer of rust, but the conservation treatment returned the canteen to its original, shiny condition, also preventing further corrosion.
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