I just finished treatment on and helped install the Egyptian copper alloy statue of Wadjet. This object, along with many other Egyptian artifacts, are to be on display at the Brooklyn Museum in the Pharaoh’s Queens and Goddesses exhibition opening March 23rd. Conserving this object has been quite an interesting experience for me.
The primary concern with the statue was that it had some severe areas of bronze disease, pictured at right. Bronze disease is a destructive corrosion process that occurs from the reaction of chlorides on copper in the presence of moisture and oxygen. This type of degradation process produces bright green powdery spots of corrosion while simultaneously eating away at the metal. Once begun, this reaction is very difficult to stop unless one or more of the reacting compounds (chloride, water, oxygen) are removed.
Unfortunately, bronze disease occurs in many archaeological copper-alloy objects given that they often accumulate chlorides during burial. Once the objects are excavated, the moisture and oxygen present in the atmosphere can catalyze the destructive corrosion process. Preventive methods such as elimination of moisture in the form of environmental regulation can sometimes prevent the outbreak of bronze disease, however very often the object will need to be physically treated by a conservator. This was the case with the Wadjet statue.
For treating the statue for bronze disease I first mechanically removed the bright green copper corrosion products, primarily on the bottom of the statue, with small hand tools. Following this, the areas affected by corrosion were chemically treated with a corrosion inhibitor. The inhibitor reacts with the metal to form a stable surface. Preventive methods including reducing the relative humidity (moisture) have been introduced into the exhibition area to ensure that the bronze disease is abated. Pre-treatment and post treatment images of the bottom of the statue are pictured below. I know that Lisa is currently working on copper alloy coins on the dig, which may have the same type of corrosion problems. If so she will treat these coins in a similar manner.
During treatment of the statue, a modern plaster fill on the base of the figure’s throne was removed. This action was taken because the plaster was exacerbating the bronze disease by holding moisture at the metal surface. Upon removal of the plaster fill an exciting find was unearthed – an animal skeleton. See image below. After discussion with colleagues and some research, it was discovered that these bones might possibly be ichneumon or Egyptian mongoose bones. Some literature indicates that seated, bronze Wadjet figures, such as the one being discussed, were often used as coffins for ichneumon. The ichneumon, revered for its ability to kill snakes and crush crocodile eggs, became a sacred animal of the goddess Wadjet in the Late Period.Jakki Godfrey