Conservation Science Then

When the Harvard chemists received the bronzes from Nuzi in 1928 and 1931, they were still experimenting with ways to stabilize or remove chloride salts while attempting to get rid of unwanted mineral encrustations. Electrochemical and electrolytic treatments gained currency because of their expediency. An object could be immersed in an electrolytic solution, which contained ions that allowed the passage of an electric current. In electrolytic treatments, the current was introduced from an outside source; in electrochemical treatments, it was generated through the immersion of the bronze object and another metal. In both instances, the migration of electrons from the bronze caused the extraction of corrosion products such as chlorides; at the same time, hydrogen bubbles that were generated by the reaction helped push off the corrosion products, leaving—so it was thought—the original object intact. Such treatment methods, however, sometimes resulted in pitting, loss of detail, and random redeposition of copper on the surface. In extreme cases, a highly mineralized object put in an electrochemical bath dissolved into a heap of powder.

The Fogg Museum’s chemist, Rutherford John Gettens, treated several of the metal artifacts from Nuzi.1 He also used them to experiment with ways to determine the condition of archaeological bronzes and thus help to select the most appropriate treatment method. As a result of electrolytic treatment experiments, an innovative use of cross-section analysis, and X-radiography, Gettens made several important discoveries. Within the clearly defined multilayered structure of the mineralized crust, he was able to locate and identify the layer responsible for “bronze disease.” And he found that a bronze object’s form and rigidity could be restored through the electrolytic method only when the metallic core was preserved and surrounded with cuprite, a copper oxide.2 These were important additions to the contemporaneous knowledge of bronze conservation.