Two Chemical Groups of Dichroic Glass Beads from West Africa

Certain blue glass beads from west African archaeological sites have been found by X-ray fluorescence analysis to fall into two chemical groups. Each group includes beads which exhibit blue/yellow dichroism' and/or cords.z Held in the hand, the dichroic examples appear blue, but against the light they appear greenish-yellow. One group of dichroic and corded beads appears to belong to the glass industry of Ife, and that relationship will be discussed in a forthcoming report. The present article presents the two chemical groups and discusses possible relationships between them. The blue dichroic beads are the subject of a tangled literature dating back at least to I603 (Zecchin I955; I964). It has not been previously recognised that the corded beads belong with the dichroic; in fact, forms intermediate between the two are found. Dichroic beads are considered by modern scholars to fall within the 'akori bead' problem, the main point of which is to define the word 'akori'. Some two dozen accounts spaced over about four hundred years allude to, or partially describe 'akori' beads (spelled variously 'accarey', 'aggrey', 'cori', etc.). Taken together the accounts are contradictory and ambiguous with respect to the name, colour, material, and source of akori. Reconciliation of these accounts by recent authors has yielded some consensus (Fage i962;Jeffreys I96I; Kalous I966; I968; Mauny I958; I96I); however, this has the drawback that historical accounts which may have applied to different things have been blended to form a rather syncretic picture, which consequently may contain anachronisms and other difficulties. The consensus view postulates the existence of both 'true' and 'imitation' akori. The 'true akori' are claimed to be made of an unknown material, while the imitations are of glass. 'True akori' were collected in the area (generally from either the ground, old graves, beside water, or the hinterland) from Dahomey to the Cameroons (Braun I624; de Marees I602; du Casse c. I688; Ruiters I623; Romer 1769; Ryder 1959); and in the sixteenth century, in Manicongo as well (Anon. c. 1540). They were purchased by Europeans and taken to the Gold Coast (Ghana) where they were sold (Anon. c. I540; Braun I624; de Marees I602; du Casse c. i688; Pereira c. I508; Ruiters I623; Ryder I959). By the nineteenth century, they were found in the hinterland of the Gold Coast as well (Bowdich I8I9). There are many other beads found in west Africa that are not claimed to be akori. Although most frequently blue, akori beads occur in many different colours. True akori were said to be worth their weight in gold. They apparently softened