Technical Glossary of Ironworking Terms.

From 'Early metal working in Sub-Saharan Africa: A review of
recent research'.
By Duncan E.Miller and Nikolaas J.Van der Merwe.
From Journal of African History, 35 (1994) pp.1-36

The veracity of a measurement. In radiocarbon dating the degree of
correspondence between the true (unknown) age and the physically determined

Adit A horizontal mining tunnel.

Agglomeration The formation of a lump by the coalescence of smaller

Archaeometallurgy The study of archaeological metal processing waste and
intentional metal products in order to reconstruct the processes used, to infer the
technological skill of the manufacturers, and to derive a record of the human
choices, decisions, and influences involved in metals production and use.

Azurite Hydrated copper carbonate (2CuCO3. CU(OH)2).

Bag bellows. Bellows, often made from a whole goat's skin and operated by
hand to force air into a furnace pipe or tuyere.

Blast furnace A conical stack operating at high temperature under forced
draught, usually using coke as fuel, and in iron smelting producing liquid cast

Bloom The product of a bloomery furnace - a fused mass consisting of metallic
iron, charcoal, unreduced ore nodules, and frequently pieces of ceramic furnace

Bloomery process A variety of iron smelting processes in which ore is
reduced to metal predominantly in the solid state at relatively low temperatures.

Bowl bellows Bellows constructed by attaching a leather diaphragm to the top
of a ceramic or wooden bowl and operated by hand or with a stick attached to the
centre of the diaphragm so as to drive air through an integral exit pipe into a

Bowl furnace A furnace consisting of an open or covered bowl-shaped
depression in the ground, which may or may not be lined with ceramic or a layer
of refractory stones.

Bowl shaft furnace A bowl furnace with a superimposed shaft to provide
greater volume and a better draught.

Brass An alloy of copper with zinc.

Bronze An alloy of copper with tin.

Calcrete A surfical rock consisting mainly of calcium carbonate (CaCO3).

Calibration In radiocarbon dating, the practice of relating the probability
distribution of a dating determination to the range of corresponding calendar
vears. This is necessary to take into account natural fluctuations in the production
of 14C and is done by reference to curves derived from radiocarbon dating
known-age material such as discrete rings of long-lived trees whose age can be
determined by counting the annual rings.

Carbon monoxide A reactive gas (CO).
Carburization A process in which the carbon content of a steel is increased bv
diffusion of carbon into the alloy.

Cassiterite Tin oxide (SnO2).

Cast iron An iron-carbon alloy cooled from a completely liquid state with a
carbon content above 2 per cent, and with a minimum melting temperature of 1
143 °C at the 4-3 per cent carbon level.

Casting The process of shaping an artefact by pouring molten metal into a

Charcoal Incompletely combusted wood providing a highly porous carbon-rich

Crucible A refractory ceramic bowl in which glass or metal can be melted.

Crucible furnace A smelting furnace incorporating a ceramic bowl in which
the molten product is caught or retained.

Decarburization The process of carbon loss by diffusion of dissolved carbon to
the surface of heated steel.

Drum bellows A synonym for bowl bellows, usually implying that the bowl is
made of wood rather than of ceramic.

Equiaxed grains Grains of more or less equal size and equidimensional shape.

Fayalite Iron silicate (2FeO.SiO2).

Ferrite The alpha form of iron containing up to 0-02 per cent dissolved carbon
at 727 c.

Flux An additive, often lime, employed to lower the melting temperature of the
slag minerals and to promote smelting at lower temperatures than would be
possible otherwise.

Forced draught The active provision of air to a furnace by means of bellows.

Forge A hearth, often with air provided by bellows, used for reheating metal
during hot-working to fashion it into the desired shape.

Forging The process of working a piece of metal while hot.

Furnace An oven or containment in which a charge of ore and fuel can be
heated sufficiently to allow smelting to take place.

Galena Lead sulphide (PbS).

Gangue The non-metallic, usually siliceous, component of an ore.

Gossan The leached and oxidized weathered cap frequently present on the
exposed surface of metal-rich geological occurrences.

Haematite Iron oxide (Fe203).

Heat treatment A variety of processes in which the physical properties of a
piece of metal may be altered by controlled heating and cooling.

Ilmenite Iron titanium oxide (FeO.TiO2).

Lamp black Finely comminuted carbon deposited as soot.

Laterite A leached soil, typical of tropical weathering, in which residual iron
oxide and silica are the major components.

Lime Informally denotes calcium oxide (CaO) or calcium carbonate (CaC03),
usually derived from shells or the surface rock calcrete, and used as a flux.

Magnetite Iron oxide (Fe304).

Malachite Hydrated copper carbonate (Cu2(0H)2CO3.Cu(OH)2).

Natural draught The passive provision of air to a fumace by exploiting the
chimney effect of hot gasses rising up the furnace to draw in air through
numerous tuyeres at the bottom.

Non slag-tapping furnace A furnace in which the molten slag collects near
the bottom of the furnace and is retained until the end of the smelt.

Nucleation The initiation of crystallization at discrete sites in a molten mass.

Ochre Hydrated iron oxides used as pigments.

Old wood problem Radiocarbon dating dates the event of the tree la! laying
down the particular wood material dated. The use of a large tree laying down
relatively old wood, or the use of old dead wood for fuel can result in an error of
hundreds (and possibly even thousands) of years to radiocarbon dates run on
charcoal assumed to be Contemporaneous with the event Or structure being

Oxidation 'I'he chemical combination of oxygen with an element or
compound to form an oxide.

Oxidizing atmosphere A gas atmosphere which promotes oxidation by the
predominance of carbon dioxide over carbon monoxide.

Partial reduction The incomplete reduction of an ore, resulting in some metal
and some roasted or fused ore, or the presence of unreacted gangue materials in
the smelting product.

Pisolitic structure A texture consisting of small (c. I to 5 mm diameter)
spheres, often comprising concentric shells of mixtures of iron oxides and silica,
typical of laterites.

Pot bellows A synonym for bowl bellows.

Precision In radiocarbon dating, a measure of the reproducibility of a date
determination. It is expressed as a plus/minus value after the mean date and is the
standard deviation associated with the determination. Precision is distinct from

Pseudomorph An object displaying an inherited form indicative of the
replacement of the original material by a secondary material.

Pyrolusite Manganese dioxide (MnO2).

Quartz Silica or silicon dioxide (SiO2), the predominant constituent of most

Quenching A heat treatment involving plunging a hot metal object into a
relatively cold liquid to produce a controlled microstructure and thereby alter the
physical properties. In the case of carbon steels this can harden and embrittle the
metal very significantly.

Reducing atmosphere A gas atmosphere which promotes reduction by the
presence of significant quantities of carbon monoxide relative to carbon dioxide.

Reduction The chemical removal of oxygen from a compound.
Roasting Relatively prolonged heating of ore nodules on open fires to induce
drying, cracking, partial break-down of sulphides, and to facilitate subsequent
smelting .

Shaft furnace A smelting oven incorporating a cylindrical or conical chimney,
or shaft.

Slag pool A puddle of molten slag, either trapped in the bottom of a non
slagtapping furnace or drained to the outside from a slag-tapping furnace.

Slag-tapping The practice of opening the base of a furnace during operation to
drain the accumulated slag and allow the smelt to proceed without blocking the
tuyere with slag.

Slag The molten, or solidified, waste product of smelting, consisting of used
components derived from the ore flux, fuel, and furnace lining. Slags can vary
significantly in composition and microstructure and contain chemical and
mineralogical information crucial to the reconstruction of furnace operating

Smelting The process of chemically reducing an oxide ore to a range of
products including workable metal by the application of heat in a furnace.

Smithing The process of chemically reducing an oxide ore to a range of products
including workable metal by the application of heat in a furnace.

Solidus temperature The temperature at which a melt of any particular
composition solidifies by crstallization

Specularite Lustrous platy haematite, iron oxide (Fe2 03)

Spherulitic structure A texture, commonly found in latterites, consisting of
small spheres of iron oxides and silica often displaying a concentric internal
structure. If the spherules are small the structure is described as pisolitic.

Stack The conical or cylindrical shaft of a furnace, usually applied to a blast

Standard deviation A statistical measure of the precision of a measurement,
which in radiocarbon dating is quoted usually as + 1 sigma, implying that the true
measurement value lies between the stated limits with a probability of 68 per

Steel An alloy of carbon in iron in which the carbon content lies between about
0.05 and 2-0 per cent.

Sulphide ore In the context of ancient metallurgy, copper sulphide ores
typically found at some depth below the oxidized and leached surface outcrops
which were the initial target of early mining.

Surface tension The cohesive force associated with the surface of any liquid.

Tempering The heat treatment of a quenched metal at a moderate temperature
of about 500 °C to allow partial recrystallization to take place in order to reduce
the brittleness of the as-quenched material.

Thermoluminescence A dating technique which relies on detecting the energy
accumulated over time of radiation-induced defects in some crystalline materials
which release this energy as light when heated.

Tuyere An air pipe through which air is either pumped or drawn into a furnace.

Valveless bellows Bellows without inlet valves, which rely on a loose fit
between the bellows outlet and the tuyere to allow air to be sucked in through
this gap.

Wire drawing A technique for thinning a metal rod by drawing it through
successively finer perforations in a plate.

Wustite An oxide of iron with the approximate formula of Fe(1-X) O.

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