Aluminium, Tin, Zinc, and their alloys
Although aluminium is the most common metal, it cannot be produced without employing industrial-scale processes. It does not occur naturally in metallic form, and extracting it from its ore demands more energy than can be accomplished by smelting. Ghana is a major source and producer of aluminium, but only since the construction of the Volta Dam made large amounts of electricity available to process it. Many everyday utensils produced commercially from aluminium are used throughout Africa; some forms are made by local metal workers using traditional casting methods, possible since the melting point of aluminium is 659°C. Ref: Historical Atlas of Africa, Cambridge Encyclopaedia of Africa.
Tin is found in large quantities in Nigeria, also to a lesser extent in the Democratic Republic of Congo and South Africa. On the Jos Plateau area of central Nigeria, tin was extracted from cassiterite by smelting, and cast into ‘straws’, used as currency.
Zinc is not produced in great quantities in Africa, only about 5% of world production. It has never been worked indigenously. The source of the zinc in the figures from Cameroon is impossible to establish; the variable amounts in the different figures would suggest that the alloy metals used in casting were scrap pieces, such as printing plates or battery linings or even imported zinc statuary, although the absence of aluminium is difficult to explain. Ref: Conservation of a group of metal figurines from Cameroon.
‘White-metal alloy’ is as generic term covering alloys with varying proportions of metals such as aluminium, zinc, tin, chromium, lead, nickel, mercury, but not excluding darker metals such as copper, and possibly some silver, but excluding iron in any quantity, because of its effect of raising the melting temperature above what is practical. Much of the African caster’s raw material consists of non-ferrous scrap metal from a wide variety of sources, such as old utensils, batteries, bullet cases, car parts. The precise make-up of the alloy is not as important to the caster as the colour and overall appearance of the finished product.