2 COLLECTION AND TREATMENT HISTORY

In 1897, the British military conducted a campaign against the kingdom of Benin (part of present-day Nigeria) in retaliation for the ambush and murder of the newly appointed colonial commissioner. Following the destruction of Benin City and the exile of the king, the military claimed as war prize a large number of cast copper alloy objects, now commonly known as the Benin “bronzes.” (Most Benin castings are technically brass.) Once in Europe, the castings were distributed among collectors, dealers, and museums.

The object under consideration, a hollow cast male head dating from the late 15th to early 16th century (NMAfA 82-05-002), had once belonged to the British general Augustus H. L. Pitt Rivers, who was a private collector and an early contributor to anthropological theory. The African art historian William Fagg has commented that most of the Benin heads from this period no longer retain a naturally patinated surface “due to the attentions of zealous housemaids” (Bassani 1991, 61). More specifically, Fagg has reported that the Benin objects in the general's care were given a protective coating of neat's-foot oil, a preservative more commonly used on cricket bats. On arrival at the National Museum of African Art (NMAfA) in 1982, the head exhibited an even olive-green coating that was wet in appearance in some areas (fig. 1). While the NMAfA curators found the object's surface aesthetically unacceptable, they were aware that the metal beneath probably had not retained its original patination. They were particularly concerned that the Western coating may have caused areas of uneven corrosion or that the surface had been stripped to bare metal before being coated. In addition, the inner surface of the head exhibited powdery, blue-green corrosion, probably a copper formate (Hopwood 1984).

Fig. 1. Detail during 1984 treatment, male head, Edo peoples, Benin kingdom, Nigeria, late 15th–early 16th century, copper alloy and iron, height 8� in. The partially cleaned surface, left side, shows the olive-green coating. National Museum of African Art, purchased with funds provided by Smithsonian Collections Acquisition Program, 82–05–002. Photograph courtesy of NMAfA Conservation Archives

As a new member of the Smithsonian Institution, the NMAfA remained in a group of 19th-century townhouses on Capitol Hill while awaiting completion of its building on the National Mall; the museum was without a professional conservator of its own. Consequently, in 1984, a consulting conservator was asked to advise on the best treatment approach for the head. In trial tests, the conservator found that a solvent cocktail (toluene, ethanol, ethylene dichloride, Cellosolve, and Cellosolve acetate) applied with swabs easily removed the olive-green coating.1 Beneath, the metal surface appeared to be in good physical condition and aesthetically acceptable to the NMAfA curatorial staff (fig. 1). Cleaning of the entire piece proceeded to complete removal, at least visually. The copper formate corrosion products were removed mechanically. Following this treatment, as a precaution against further corrosion, the Benin head was given two coats of Incralac (methyl methacrylate copolymer with benzotriazole) followed by a final layer of Renaissance wax (microcrystalline-polyethylene wax blend) and returned to the old NMAfA building for exhibition.

In October 1991, the Benin head was lent to the National Gallery of Art, Washington, D.C., for exhibition in Circa 1492: Art in the Age of Exploration. For several years, the curators had noticed an accumulation of lint and dust on the piece and, in some areas, the 1984 wax coating had become clearly visible as a white haze on the metal surface; casting details seemed muted and flattened (fig. 2). On the object's return from the National Gallery, it was decided to take advantage of the interim period before reinstallation in the gallery, when the object would be in storage, to investigate a reversal of this last treatment.

Fig. 2. Male head after 1984 treatment, showing lacquered and waxed surface. Photograph courtesy of NMAfA Conservation Archives

In addition to concerns about the aesthetic problems caused by the coating already noted, it was felt that any protective function the wax might have afforded was no longer required at the new museum building, where exhibition cases are constructed of high-quality materials and where the relative humidity is easily controlled on a general as well as a microenvironmental level. Moreover, Fenn and Foley (1975) reported that industrial research on several types of coatings, including wax, indicates that they do not provide an impervious barrier to water and oxygen, although they may offer protection from contamination during handling. Incomplete or damaged coatings may create electrochemical cells that encourage corrosion to proceed at the points of imperfection. Finally, the Benin head also had been coated with Incralac, which has been shown to age poorly under certain conditions (LaFontaine 1981; Erhardt et al. 1984). These factors, coupled with the aesthetic problems, intensified the desire to remove the lacquer as well as the wax and to leave the surface of this object coating-free, if possible.