Recovering the Brilliance of a Benin Bronze
Ellen G. Howe, Conservator Emerita, Department of Objects Conservation
In traditional lost wax casting, also known as cire-perdue, a model, sometimes with a clay core, is created out of wax and then coated with a fine layer of clay known as "investment." More layers of courser clay are applied on top to create the mother mold. When the mold is heated, the wax is melted out, leaving a cavity into which the molten metal is poured. To retrieve the cast metal object, the mold is broken away and the surface is cleaned.
In 1897, English soldiers seized the Horn Player and other cast brass sculptures from the royal court of Benin City, located in modern-day Edo State, Nigeria, in the Punitive Expedition. Once they were shipped to Britain, the royal sculptures were acquired by English and European collectors who praised their artistic and technical brilliance, especially noting the Benin skill in lost-wax casting, long associated with Renaissance sculpture. "These Benin works stand among the highest heights of European casting," wrote Felix von Luschan, a curator at the Ethnological Museum of Berlin. "Benvenuto Cellini could not have a made a better cast himself, not anyone before or after him, even to the present day." 
Horn Player, 1550–1680. Nigeria, Court of Benin, Edo peoples. Brass, H. 24 3/4 x W. 11 1/2 x D. 6 3/4 in. (62.9 x 29.2 x 17.2 cm). The Metropolitan Museum of Art, New York, The Michael C. Rockefeller Memorial Collection, Gift of Nelson A. Rockefeller, 1972 (1978.412.310)
While in England, the sculptures were coated with a layer of oil varnish and pigmented wax in a manner typical of practices used for caretaking and exhibiting Western sculpture at that time. In 1980, conservators at The Met began to remove these dark, colonial-period coatings in order to reveal the material nature of the surfaces below. Using careful solvent cleaning under high magnification, their work has revised our understanding of these works' original appearance, suggesting that brass production in Benin City fundamentally differed from methods prevalent in late nineteenth-century Europe.
In the Edo language, the phrase "to commemorate" (sa-e-y-ama) means literally to cast a form in brass, an alloy of copper and zinc whose color can vary from a reddish to a golden yellow. Figures such as the Horn Player, placed on court altars in memory of kings and historical events over a period of centuries, were reportedly kept bright and "very clean" (i.e. polished), both the metal and its brilliant color having ritual and royal connotations in Edo tradition. In modern-day Benin City, contemporary cast-brass casters continue to produce brass that is kept shiny and lustrous. The Horn Player, although originally meant to be seen with a polished surface, has long since acquired a greenish-brown corrosion layer resulting from years of exposure to the atmosphere.
Another feature of the Horn Player's current surface is the reddish-brown particulate matter visible in many of the figure's crevices. On other Benin sculptures, this opaque reddish coating is even more abundant, and can be seen in both deep and shallow recesses of the cast decoration.
What is this red-brown material, and why is it still present on Benin sculpture? Many believe that the red patina is merely wind-blown soil, the "red dirt of Benin" as described by British soldiers who collected the sculptures from palace storerooms. However, conservation treatment has shown us that rather than a friable layer of dust it is a very hard and compact material, difficult to separate or remove from the metal surface. Modern analysis has identified the red material as a fine iron-rich clay identical to the clay used for the casting core, and that it exhibits some mineralogical characteristics of a material subjected to high heat. This suggests that the material is actually the remains of the original fired investment layer, the initial clay coating that was applied to the surface of the wax model but never completely removed from the cast metal after firing.
In Western casting traditions, all traces of the investment are usually removed from the cast sculpture to reveal a smooth, metallic surface that can then be patinated. On Benin sculptures, varying (and sometimes quite substantial) amounts of what appears to be investment may have intentionally been left in place as an intrinsic part of the sculpture.
It is currently difficult to know the exact purpose of this residual clay layer and how it originally affected the appearance of the freshly cast and brightly colored brass. Perhaps its reddish color acted as a form of pigmentation, enhancing the metal's ritual power and prestige, while at the same time serving to highlight the decorative details of the cast metal surface. Perhaps by its very presence, the red soil of Benin—a likely remnant of the casting process—refers to the ritual importance of brass production and the origins of Benin's royal sculpture
 Kathryn Wysocki Gunsch, "Art and/or Ethnographica?: The Reception of Benin Works from 1897–1935,” African Arts, vol. 46, no. 4, 2013, p. 31.
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