The Composition of Ife Heads - A Numerical Analysis

Among the most famous of the West African brass sculptures are the eighteen naturalistic portrait heads discovered in Ife Nigeria, in 1938. Recently, an exhibit of these heads together with other brass, terracotta and stone artifacts from Ife, toured selected museums in the UK and USA(I). This exhibit caused many viewers to reconsider their opinion that African art is the work of a primitive people. These remarkable artifacts are equal in workmanship and artistry to sculpture made during the European Renaissance.

Ife tradition claims that brass casting began during the reign of the Oni Obalufon and that his craftsmen made the Obalufon mask(II). Archaeological excavations in Ife have not revealed any evidence of metal casting, not even the most primitive of metal objects. This has led to speculation among the African art historians as to the origin of the Ife heads. A number of theories have been advanced:

• Leo Frobenius, during an expedition to Nigeria from 1910-12, was shown the brass Olokun head, the Obalufon mask and various terracotta heads. He was astonished by the quality and artistry of the objects and questioned their African origin. He wondered whether he had found evidence of an African Atlantis(III).
• Frank Willett proposed that the Ife heads were used as funeral effigies for various deceased Onis of Ife, and were the product of different sculptors working over several centuries. This hypothesis is still accepted by many African art historians(IV).
• Kenneth Murray, suggested that “only one artist, working for a couple of years, made the majority of the heads.” His reason for this conclusion was based on the heads’ stylistic similarities(V).
• William Fagg pointed out that all the Ife heads had a couple of features in common; the mouth was displaced by about 6 millimeters from the midline of the face and the corners of each mouth ended in a depression or dimple. He considered that these “two artistic peculiarities are a mannerism of the artist rather than fidelity in portraiture.” Portraits painted by some Renaissance artists have the same artistic peculiarities(VI).
• Stefan Eisenhofer is of the opinion that the Ife heads can only be dated to some period before 1700 AD(VII). Thermoluminescent analysis of core samples taken from the interior of two of the heads gave the following approximate dates: 1440 +/-65 A.D and 1490 +/-85 A. D. possibly dating the Ife heads to the latter part of the 15th century(VIII).

The Ife heads fall into two groups; six were cast from almost pure copper (data not given), the remaining twelve from brass. Chemical analysis of the brass is presented in Table I(IX). The sample numbers are assigned by Underwood(X).

The Europeans used the cementation process to manufacture brass until metallic zinc was isolated in the 18th century. During the Roman era, cementation involved smelting copper with a mixture of zinc ore (calamine/zinc carbonate) and charcoal. The charcoal reduces zinc ions to vaporized zinc. The molten copper absorbs the vapor. This process produced a brass containing less than 10% zinc. In the 15th century, the calamine was first roasted in a wood fire to zinc oxide. Crucibles, packed with layers of ground zinc oxide mixed with powdered charcoal and copper granules were heated in a furnace to a temperature of 1000 °C +/-100 °C(XIII)(XIV)(XV)(XVI). This temperature is sufficient to reduce the zinc ions to zinc vapor, but not high enough to melt the copper (melting point 1083 °C). The vaporized zinc permeates the surface of the copper granule. The color of the fumes emitted from the crucibles were used as a guide for controlling the temperature of the furnace. Finally, the temperature was raised sufficiently to melt the copper, and the brass was poured into molds. A brass containing 28% by weight in zinc is the highest concentration of zinc this method can produce(XVII).

One drawback to making brass using the cementation process was that the uptake in zinc could not be easily determined(XVIII). However, the 15th century metallurgists had observed that during the initial heating of the copper granules with charcoal and zinc oxide, they gained weight, reflecting the uptake in zinc. The composition of the brass may be calculated by weighing the copper granules before and after heating. Therefore brasses of lower zinc to copper ratios may be produced by the addition of an appropriate weight of copper to the molten alloy whose uptake in zinc had previously been determined. This would require using a crucible with a lid and covering the molten alloy with melted glass to prevent loss of zinc. Whether this was actually done is not known.

The brass Ife heads have an unusually high lead content. Werner and Willett suggested that the ores used to cast these heads came from the Harz region of lower Saxony. They postulated that various leaded zinc ores when cemented with copper, would produce the percentages of copper, zinc and lead given for the brass Ife heads in Table I . However, the presence of 2% lead prevents the absorption of zinc by copper by 4%. Head 8 contains 71.8% copper, 15% zinc and 11.1% lead(XIX). A leaded zinc ore containing 11.1% lead would produce a brass containing about 6% (28 – (4 * 11 / 2)) zinc. This head was therefore made by adding refined lead to the molten brass in the melting pot. The same argument holds for the other brass heads. Figure 2 in Werner and Willett’s paper, gives a plot of the percentages of lead vs zinc given in Table I. This plot shows graphically that the percentages of lead fall into three groups, with mean values of 5.47%, 10.94% and 14.45% respectively. These means are approximately in the ratio of 1:3:4. Some heads received 1 bar, others 2 bars and others 3 bars of lead. Lead isotope analysis showed that the lead in heads 1, 8, 9, 12, 15 and 16 were from the same source and heads 2 and 11 from a different source. The source of the lead would not matter, provided that all the bars weighed the same. If lead bars were available, it is reasonable to assume that copper bars were used to cast the six heads made from almost pure copper.

The only refined source of zinc in the 15th century was brass. I assumed that the zinc in each head came from a brass containing the same amount of zinc as the brass head containing the highest percentage zinc, namely head 8. If the percentages of lead and the minor impurities are ignored, the composition of the brass present in head 8 can be calculated. Head 8 contains 15.0% zinc and 71.6% copper. This head may have been cast from a brass containing 17.3% zinc (100*15.0 / (71.6+15.0). This represents a brass with the lowest concentration of zinc that can be used to cast all the heads. If 17.3% brass is substituted for the zinc in the other heads, then additional copper is required. Table III shows the percentages of 17.3% brass in column C, and copper in column D, required for each head to have the same percentages of copper and zinc as in Table I.

I experimented with brass containing higher concentraions of zinc, but did not obtain the same uniform pattern of results that 17.3% brass produced.

Table III shows the following:

Table IV, makes the assumption that a total of approximately 24 brass and copper bars combined, went into the melting pot to cast each Ife head.

An initial survey of the results obtained from the chemical analysis of the brass Ife heads (Table I) suggested that refined metals were used to cast these heads. The only assumption I made was that the zinc in all the heads was replaced by a brass whose composition is that of the head with the highest percentage of zinc. The other heads required the addition of copper to the brass in order to duplicate the percentages of copper and zinc in Table I. Sufficient quantities of brass, containing the same percentage zinc had to be available to cast all the heads. The cementation process may have been adapted to produce brasses with different percentages of zinc.

It is difficult to believe that the data presented in Tables III and IV is meaningless. It fits together too well and supports some of the hypotheses presented by many African art historians. The results from Tables III show that the copper and zinc percentages in Table I, may be duplicated by using an appropriate combination of brass (17.3% zinc after remelting) and copper bars. The means were obtained by averaging the three clusters of lead in Table I. These means fall approximately into the ratio, 1:2:3, indicating that lead bars of similar weight were added to the pots containing molten brass and copper. Table IV shows that approximately 24 bars of copper and brass, may have been used to cast these heads and that both the copper and brass bars weighed about the same amount. Based on the weight of a single head, the brass and copper bars weighed approximately 312 gms and the lead bars weighed approximately 466 gms.

The Ife heads, with the exception of head 13, all have the same fingerprint of trace metals, indicating that the copper came from the same mine. This supports Kenneth Murray’s hypothesis that the Ife heads were made in the same workshop at about the same time. William Fagg’s observation that all the heads show the same modeling characteristics indicates that the same artist modeled all the heads. Since Nigeria has no copper deposits, the metals would have been mined and refined in Europe then transported to Nigeria. As there is no archeological evidence that Ife had any kilns, the artist who produced these flawless castings using the difficult and exacting lost wax process probably had a workshop elsewhere.