Glossary of terms used in the study ancient metal-working A

Glossary of terms used in the study of ancient metal-working

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Face-centred cubic, FCC: A material with a face-centred cubic structure has an atomic lattice with an atom at each corner of a cube and an atom at each centre of the cube faces. The structure can also be considered as layers of close packed spheres stacked on top each other in the order ABCABC. This structure is the most compact way of filling space with uniform sized spheres. ** Hence, this structure has been called close packed cubic in the past. Face-centred cubic metals tend to be soft and easily worked, such as silver, aluminium, gold, copper, lead, and platinum. Iron at elevated temperature takes on the FCC structure (austentite).
Fahlerz: A name, meaning grey or 'pale ore' is applied to ores in which the tennantite - tetrahedrite minerals are the principal component. The series copper-rich mineralisation with arsenic (Tennantite) and antimony (Tetrahedrite) end members. The mineral series may also contain additional elements such as silver, nickel, bismuth, cobalt. Thought to be a major ore source for some Bronze Age central European and Irish metallurgical traditions, as well as the alloy used to produce medieval domestic ware in Britain.
Fayalite: The iron silicate Fe₂SiO₄ which has the crystal structure of the mineral class olivines. It is a common constituent of many metal-working slags, particularly bloomery smelting, iron smithing and copper smelting slags. It is often observed as elongate faceted laths. Other olivines such as kirschsteinite CaFeSiO₄, (kneblite?) Mn₂SiO₄may occur in slags.
Fayalitic Slag: A slag in which fayalite is the major component.
FCC See Face CentredCubic
Feeder (casting): Most alloy compositions freeze over a range of temperatures, and most metals contract on solidification from 2 to 7%. Without the provision of a supply of liquid metal to fill the spaces and porosity formed due to this shrinkage the casting may be unsound. This is especially true of larger casting which take longer to freeze. A properly located and designed header and feeder will help to eliminate this problem. The weight of metal in the header-feeder components of the casting may comprise up to 40% of the total weight of the casting, however, this metal would be cut off and recycled. But such a technique was rarely necessary in the thin castings of the Bronze Age.
(related - header, mould)
Feldspar: Two series of alumino-silicate minerals that are important class of rock forming minerals. The two series are the plagioclase feldspars in which form a continuous solid solution series between the sodium (albite) and calcium (anorthite) rich end members, and the alkali feldspars with a full range of solid solutions between the sodium (albite) and potassium (orthoclase) end members. However, there is only a limited range of solid solubility between orthoclase (potassium) and anothite (calcium) members. The last component to freeze in many slags have compositions that are close to the composition of anorthite or more rarely orthoclase/leucite.
Ferrite: The low temperature body centred cubic form of iron, almost devoid of carbon but capable of containing various amounts of other elements such as phosphorus. Below the Curie temperature (*C in pure iron) this form of iron is magnetic.
Ferritic iron: Iron consisting mainly of ferrite, this is with insufficient carbon or phophorus to harden the metal significantly.
Related terms: Phosphoritc iron
Fettling: The verb to fettle means to make ready, or to put in order. It is used in a number of metallurgical contexts. In the case of furnaces, it means the repairing of minor defects in the lining with lute. With castings it is applied to the process of cleaning off the moulding sand and removal of flash and feeders. Similarly, it has been applied to the removal of slag and gromp from the raw bloom prior to forging into a billet.
File: 1)    A tool with ridges or teeth formed by two intersecting sets of ridges, used shape and finish wood and metal.
2)    To file; to use a file to shape wood and metal.
   Related Whetstone, hone stone, touch stone, burnisher
Filing: Removal of metal with a file. Filing is uncommon in ancient metalwork, as the tooth spacing of most early files tended to be rather coarse thus more suitable for woodworking than metal working. It is likely that stone abrasives were the prefered method of final shaping, finishing.
Finery: A hearth in which cast iron was converted into wrought iron by melting and oxidization in an air blast. The process differs from puddling in that the metal and fuel are together in the same hearth. This means that it has to be fuelled using charcoal not coal or coke as the sulphur for these fuels would contaminate the metal and make it hot short
Related terms: Chafery, puddling furnace.
Finery Forge
Fire-setting: Removing rock or ore from a rock face by lighting a fire against it. It was thought that quenching the rock with water was a necessary step. But in most circumstances fact that the natural expansion and contraction of the rock, and the combination of difficulty of getting water water to the site, the time necessary to clear the area of fumes means that water quenching would do little to aid the process.
Flan: An intermediate product (blank) from which coins are struck.
Flapping: Rarely used term for stirring the surface of a bath of molten copper for the removal of impurities by selective oxidation.
Flux: A substance added to a (typically oxide) system to lower the melting point. Fluxes for copper alloy.
For example, the use of silica sand during hammer welding where it combines with iron oxide to form a fayalitic melt. The addition of lime to the iron smelting charge has a slightly different function in that it replaces the iron in the slag. In that although blast furnace slags melt at higher temperatures (c. 1400^oC) than bloomery slags (1050-1150^oC) the amount of iron trapped in a blast furnace slag (2-5%) is far less than a bloomery slag (50-70%) making the process more efficient.
Folding - iron
Forge - hearth
Forge - metal-forming
Forging
Founder -
Foundry
Free-running temperature: Pure metals have sharply defined melting and freezing temperatures; glasses and slags, on the other hand, do not. They soften gradually as the temperature is increased until their viscosity is low enough to permit them to be worked or poured. The temperature at which this may be said to occur is the free-running temperature.
Fuel
Fuel Ash Slag
: A low density slag-like material - often of a light colour externally with a high silica content. Complete pieces may have rounded exteriors with no obvious points of contact with a surface on which it cooled. Although, the exact origin of much Fuel Ash slag is uncertain, they often contain, partialy fused or sintered quartz grains and other rock or soil debris. It is likely that this material is the result of a high temperature process which results in the sintering and partial melting of the non-combustible fragments in the fuel, together with material from the surrounds of the fire. There are a number of processes that could generate this type of material:- metal-working (all forms), pottery making, burning of daub during a building fire, glass-working, salt-making, cremation, or simply the burning of a fuel with a very high silica content such as bracken. References
Related terms Cinder, Clinker
Furnace: A structure in which material can be heated to high temperatures. In general, the term furnace applies to a structure with a refractory superstructure which restricts air access to the charge. Thus, allowing the operator to control the reducing condition of the atmosphere the charge experiences. This is in contrast to a hearth which is open to the air. This is in contrast to a hearth which is open to the air. However, the term hearth is used for parts of furnaces in which air and fuel first first react.
The most important distingishing feature for furnaces is whether the charge is separated from the source of combustion or not. The introduction of the reverberatory and muffle furnaces, in which the fuel is burnt separate from the charge, marked major technological changes as this prevents contamination of metal by elements such as sulphur from the fuel.
Furnace - types
Furnace parts
Furnace - Temperature
Fusion gilding

Gad(d)

An archaic term for a piece of iron or steel - usually a short length of broken rod or strip
Also the name of a type of a small pick used to break rock and ore.

Galena

The mineral lead sulphide, PbS, also was known as lead glance or blue lead. This mineral was the principal ore of both lead and silver, as some argentiferous ores may contain an appreciable amount of silver.

Galvanised Iron

In 1837 H.V. Crauford was granted an English patent for dipping in a bath of molten zinc protected from volatilisation by a layer of sal ammoniac, (ammonium chloride, NH₄Cl). This appears to be derived from the work, in the previous year, of the French chemist Sorel. In the 1840s the process was used to produce agricultural and industrial goods and corrugated iron sheet for building purposes. (Dickinson, 1943-4)
There had been earlier attemps in France, starting around 1740, to use zinc to replace tin to protect iron goods. The last of these early attemps to use zinc plating seems to have been to produce iron hammered saucepans in Rouen, France, which was abandoned shortly before 1786.

Gama-hada

Japanese decorative technique making use of immiscible metals, such as silver or silver-copper alloy droplets on iron.

Gamma iron

Another term for the face centred cubic, non-magnetic alliotrope of iron, austenite.

Gangue

The unwanted part of the ore that has been removed or cannot be removed by mineral dressing. During smelting this combines with any fluxing material that may be added to form slag.

Gassed

Some molten metals will dissolve gases, which are released upon solidification and which give rise to porosity in the casting. The term 'gassed' or 'gassy' describes the result. It can sometimes be avoided by suitable pre-treatment such as adding a small amount of cuprous oxide to a hydrogen-containing (over-poled) copper.

Gate

The narrow channels through which molten metal enters the casting (sometimes referred to as 'jets'). These are situated between the funnel-shaped runner-bush, which receives the metal from the crucible, and the casting itself. The term may combine the gates and the runner-bush all in a 'running and gating' system.

Gehlenite

A mineral, Ca₂[Al₂SiO₇], of the melilite group that may be found in slags.

German Silver

Alloys of copper, nickel, and zinc usually comprising about 52-80% copper, 5-35% nickel, and 10-35% zinc. This alloy was formerly used for many decorative purposes as a cheap substitute for silver, since it does not readily tarnish and is of silvery hue.

Gilding

The technique of covering the surface of a cheaper material with thin layer of gold. There are a number of different ways of gilding metal and non-metallic objects (see below)

Cold Mercury Gilding
Depletion Gilding
Electrochemical
Electroless
Fire: Also known as mercury gilding
Foil
Fusion: A process used in ancient South America, especially Ecquador, for the gilding of copper alloys by dipping or fusion of molten gold alloys to the surface, resulting in thick gold alloy coatings. May also be used to create silver alloy coatings over copper.
This is the precious metal version of hot-dip plating which has a wider range of applications.
Leaf
Mercury Gilding
Diffusion bonding
Laquer

Goethite

An iron oxide, alpha-FeOOH. Commonly found as a weathering product of iron bearing minerals, and forms in oxidizing conditions. It is often the main constituent of the so called 'limonitic' and bog ores. The mineral is a yellowish brown to red colour, but has a yellow streak, and dehydrates to haematite, unlike lepidocrocite (the other yellow iron 'oxide') which dehydrates to maghemite.
Related:- Magnetite, Haematite, Maghemite, Lepidocrocite, Limonite, Pyrite, Pyrrhotite

Gold

Element with atomic number 79, symbol Au, atomic weight 196.96, mp 1063 ºC, specific gravity 18.88. Native gold usually contains some copper and silver. Typical gold concentrations are 85% to 95% with the remainder being mostly silver. Gold is bright yellow, but with increasing silver content the color is white, while copper provides red tints to the color. With a platinum content of between 20 and 25% and nickel gold alloys become white.

Gold foil

A thin sheet of gold thick enough to be handled easily and support its own weight. Futher hammering will reduce the thickness still further to produce gold leaf. (Oddy A. 2000, 15)

Gold leaf

Gold leaf is so thin that it has to be handled using special techniques. (Oddy A. 2000, 15)

Gossan

The upper part of a metalliferous deposit (vein) from which the wanted metal has been leached down into the zone of secondary enrichment. This part of the vein is rich in iron, hence Cornish term Iron Hat. In regions subject to glaciation the original gossan may have been removed and not had time to reform

Grain

Most metal artefacts are poly-crystalline, that is they consist of a large number of small regions (crystals) in which the atoms are arranged in regular aligned repeating 3-dimensional arrays of atoms (unit cell). A grain is a volume in which the unit cells are all arranged parallel to each other.

Graduation

Grain boundary

Grain boundary is the interface between two or more grains. The unit cells in two adjacent grains will not be orientiated in the same directions in 3 dimensions. In such regions, the mis-match between the atom lattices mean that there will a lower density of atoms, thus grain boundaries act as paths for rapid diffusion, and sites for the nucleation anf growth of new phases.

Grain boundary segregation

The precipitation of a phase or inclusion at the grain boundaries of a polycrystalline solid.

Grain growth

The mis-match of the atomic lattices across the grain boundary means that the grain boundaries have a higher energy than the bulk of the grain. Thus, there is a tendency for the system to try to reduce this energy by the reduction of the total grain boundary area. When the temperature of the metal is high enough to allow grain boundary migration, the larger grains will tend to grow at the expense of the smaller grains.

Grain Growth - Abnormal

Grain size

Grain size, control of

Granulation

In General: When referring to cast iron, slag and other metals as well as gold, the term means the production of small solid droplets of the material. Usually this was done by pouring a thin stream of the molten material into a water bath.
In gold: This term more usually refers to the process by which small gold grains (produced by granulation or by simply melting small pieces of gold and allowing surface tension to pull the metal into a ball) were soldered (by reaction soldering or diffusion bonding) to the surface of the workpiece. Common in Etruscan goldwork.

Graphite

One of the alliotropes of carbon, in which the carbon atoms form sheets of strongly bonded atoms in a hexagonal arrange, but with relatively weak bonding between the sheets, giving graphite its lubricant properties.

Graphite Crucible

The inclusion of graphite into the body of a crucible helps to protect the melt from oxidization. Graphite was used as part of crucible fabric in Germany/Austria during the Iron Age (check period). Later the use graphite crucibles was reintroduced as both as part of the fabric and as pure graphite crucibles when more extensive graphite deposits became available.

Graphite, Kisch

Graver

A fine tool for cutting / shaving metal used by an engraver. (Also see burin)

Grey cast iron

A cast iron in which the majority of the carbon present is in the form of flakes of graphite. The presence of the graphite gives the fracture surface a characteristic grey colour - hence the name.
Related terms - White cast iron, Mottled Cast Iron, Cast Iron

Gunmetal

A ternary alloy of copper, zinc, and tin; modern gunmetals usually contain less zinc than tin, but some contain equal proportions together with lead, and have a composition such as 85-5-5-5.

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HV: Hardness on the Vickers or Diamond Pyramid Number (DPN) scale.
Hadfield Manganese Steel: with the development of high manganese, low carbon alloys in France in 1877, which had much higher manganese content than spiegeleisen . In 1887 Hadfield patented his Manganese Steel, which could not be hardened by quenching although it contained 1.2% carbon, but was tough and work-hardened rapidly.
Hammer scale: The scale removed from iron during forging. This consists of metal which has reacted with air and which has thereby been converted mainly into oxides of iron. The oxide may be shed in to the hearth and help form smithing slag, but most is formed and shed around the anvil. There are two major forms -
Hammer Weld: Hammer or fire welding is carried out at full welding heat, at which the metal is white hot, but not molten. The method relies on the ability of two oxide-free metal surfaces to weld to each other when brought together. For this to happen with iron, the iron oxide layer on the surface must be molten and free running so that it can be swept away when the surfaces are forced together by the hammer blow.
Hard Pan iron ores.: These are chemically formed iron ores which occur where a change in Eh/pH conditions cause the iron that was either in solution as ferrous ions, or was in suspension as colloid particles,are deposited as insolluble iron oxides in the soil. They can form relatively rapidly under suitable conditions (in a few decades). They often contain high concentrations of other elements, phosphorus being the most common, but may also accumulate copper and arsenic.
They can form extensive deposits in sandy iron rich soil at the level of the water table - often found in England developing on or adjacent to the Cretaceous Lower and Upper Greensands, the Tertiary sands (East Berkshire; Hengistbury Head, Hampshire), but also in sandy soils on or adjacent to the Jurassic ironstones.
Hard soldering: An alternative term for the use of a brazing alloy or a copper-silver alloy for joining, as opposed to the use of lead-tin alloys (soft solders).
Hardness: The measure of the resistance of a material to plastic defomation when indented. There are a number of different measures of hardness
Hearth
Heat - Colours
Hematite / Haematite: The iron oxide Fe₂O₃ a dense purple-black mineral with a characteristic cherry streak. Often found a dense massive or reniform formations which make it a more difficult ore to smelt by the direct process than bog/hard pan or sideritic ores.
Related - Goethite, Magnetite, Maghemite, Lepidocrocite, Limonite, Pyrite, Pyrrhotite
Hercynite: The iron aluminum spinel FeAl₂O₄, a minor mineral in many metal working slags. Shows as a slightly pink colour when compared with fayalitic under the reflected light microscope, particularly noticable when slightly out of focus due to its different birefringence. The transition elements chromium, vanadium and titanium tend to segregate to this mineral
High bloomery (Stuckofen): A developed shaft furnace capable of producing cast iron as well as a bloom.
Hollowing
Homogenization: A thermal or thermo-mechanical process designed to even out the cast-in inhomogenities in compositon or micro-structure. Usually, a combination of both annealing and mild coldworking is required to remove gross chemical segregation.
Hone: A fined-grained stone (often a siltstone or a metamorphosed siltstone) used to polish and give a final sharpening to a cutting edge.
Hot Blast
Hot-working: Deformation of the metal or alloy above the temperature necessary for the recovery processes to be fast enough to counteract work-hardening during plastic deformation. This temperature is usually about 0.3 of the melting temperature in degrees Kelvin for pure metals and 0.5 of melting temperature for alloys, if not higher for some steels.
Hushing: A method of hydraulic mining in which the barren over burden was removed by directing a stream of water down the hillside. (Expand)
HV: The units of hardness on the Vickers (VPN) or Diamond Pyramid Number (DPN) scale. **
Hydraulic Mining: Mining using water to remove the over-burden, and often to perform the initial ore benefication.
(Related terms - hushing, tin stream-works, tinning)
Hypereutectoid
Hypoeutectoid

Updated 30-Dec-05

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Terms to define - 52
Terms to be checked - 22
Terms checked - 43
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Total terms in section - 117