Alpha matrix: in a binary alloy (A-B) where A is the major element, the phase where B is in solid solution in A is often called alpha matrix (α).
Annealing (annealed): a process of heat-treatment (100-1200°C) carried out on a metal or alloy to reorganize and relax its crystalline structure while removing accumulated effects that have hardened the metal. The annealed metal is malleable again and can be further deformed. The annealing temperature never reaches the liquid state of the metal. Over-annealing (at excessively high temperature or for an excessively long period) is characterised by large grains of heterogeneous size.
Bainite: a crystalline structure that can form in tempering steels. At 200-350°C austenite can decompose into either martensite (quick cooling) or into bainite (slower cooling) which consists of a mixture of cementite and ferrite. Tempering martensite also produces bainitic structures.
Bean ore: a typical Swiss ore with complicated sedimentation originating in soils similar to laterite, also called siderolithic ore, preferentially existing in the Jura Mountains between Schaffhausen and Lake Geneva GE. It contains high Fe concentrations and equal quantities of alumina and silica. The dominant trace elements are vanadium and chrome.
Bloom: a spongy mass of iron produced in a bloomery furnace in which the Fe is reduced in the solid state and is not molten during reduction. The Fe bloom must be extensively worked at white heat to consolidate the Fe and remove excess slag and charcoal.
Brass: an alloy of Cu and Zn, with Cu as the major alloying element and with up to 40 mass% of Zn. Early brasses were binary alloys containing 90-70 mass% Cu and 10-30 mass% Zn. The colour of brass changes with increasing Zn content from a rich Cu-red through pale yellow to white.
Bronze: used since antiquity, an alloy of Cu and Sn. Usually with up to 14 mass% of Sn, but many examples of ancient bronzes are known to have higher Sn contents. 14 mass% Sn is the limit of solid solution of Sn in well annealed α bronzes. Bronzes can contain large amounts of Zn and Pb.
Carburization / cementation: process of increasing the carbon content of the surface of a metal (often wrought Fe) by heating the metal below its melting point in carbonaceous matter such as charcoal.
Casting: operation of pouring liquid metal into moulds of sand or other materials (clay, stone, metal) and allowing it to solidify.
Casting skin: thin skin of solid metal first formed on the surface of the casting and the mould wall.
Cementite: the hard, brittle component of Fe-C alloys, containing about 6.67 mass% C, corresponding to the phase Fe3C.
Cold working: the plastic deformation of a metal at a temperature low enough to cause permanent strain hardening. The treatment usually consists of rolling, hammering, or drawing at room temperature. The hardness and tensile strength are increased with the amount of cold-work, but the ductility and impact strength are reduced.
Contents: below 1 mass%: low (<100mg/kg), middle (a few hundred mg/kg) and high (>1000mg/kg).
Contextual inclusions: inclusions originating from the smelting process (charcoal, organic materials, angular rock inclusions, feldspars).
Coring: the dendritic segregation of an alloy during solidification. Compositional changes can be measured between the core and the periphery of the dendrites. Common in ancient cast bronzes. Coring is accentuated in alloys with a wide separation between liquidus and solidus curves.
Cross-section: an embedded section including a cut through an object.
Crucible: a vessel made of a refractory substance used for melting, smelting and calcining materials at high temperatures.
Dendritic structure: shaped like the branches of a tree. Dendrites are common in cast alloys and may have the appearance of an intersecting snowflake pattern. Also found in slags.
Ductility: the ability of a metal to be drawn or deformed. Ductile metals are usually face cubic centred (FCC) types.
Eh: soil redox potential or measure of the tendency of a chemical species to acquire or lose electrons, for metals E°.
Equi-axed: of equal dimensions or properties in all directions. Equi-axed grains are hexagonal in form.
Eutectoid: decomposition of a solid solution into two solid phases.
Fayalite: the most common component of ancient slag and slag inclusions. Fayalite is a Fe silicate, 2FeO,SiO2, which melts at about 1205°C, and usually takes the form of broken, elongated grey laths in silicate-based slag inclusions.
Feldspars: KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8, are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth’s crust.
Forged: formed by heating in a hearth and hot beating or hammering into shape.
Furnace: vessel made of a refractory substance that differs from crucible by the size of the reactor (much larger), source of heat (inside the reactor) and the higher yield, sometimes with blowpipes connected to the reactor.
Grain: in crystalline metals, the grain is an area or zone of crystal growth in a uniform and homogeneous form.
Grain boundary: interface between a succession of grains.
Grinding: finishing process used to improve surface finish with an abrasive material that rubs against the metal part and removes tiny pieces of material.
Hammerscale: an oxide skin that forms on heated metal and flakes off when it is hammered.
Homogenised: exposed to high temperature to ensure uniform diffusion of components.
Hot-working: deformation of the metal or alloy under high temperature.
HV1: hardness on the Vickers or Diamond Pyramid Number (DPN) scale, tested with a load of 1kp or 9.8Newton (1kilopond: force exerted by one kilogram of mass in a 9.80665m/s2 gravitational field).
Hypereutectoid: containing a greater amount of C (often of carbon steels) than that required to form a completely eutectoid structure. In steels this would require more than 0.83 mass% C, the amount needed to create a completely pearlitic structure.
Hypoeutectoid: containing a lesser amount of C (often of carbon steels) than that required to form the eutectoid structure of 0.83 mass% C. Most ancient steels are hypoeutectoid.
Ingot: metal shaped in a particular form to facilitate trade. For iron there are Spitzbarren, Schwertbarren, currency bars and (from Roman times) bars with rectangular sections of different sizes. Concerning copper alloys, the first bars have a plano-convex form or are oxhide ingots. Deposits of neck-rings and axes are also understood to be trade commodities. In later times bars of various sizes were used.
Intermetallic: solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents.
Ledeburite: eutectic of the Fe-C system, the constituents being cementite and austenite at high temperatures; cooling decomposes the austenite to ferrite and cementite.
Martensite: refers to the hard, needle like phase of quenched steel. The most common martensite appears in ancient low-carbon steels.
Mean: value obtained by adding all values and dividing the sum by the number of values.
Median: middle value in a statistical serie.
Metallic bond: electrons form a shared cloud between atoms.
Neumann bands: parallel lines in grains that are specific for P-rich Fe alloys. In Feα Neumann bands are said to develop by cold work and shock deformation.
Pearlite: the fine mixture of ferrite (Feα) and cementite (Fe3C) found in steels. At 0.83 mass% C (eutectoid composition) only pearlite is found. In most ancient steels, a mixture of ferrite and pearlite is common.
Phase diagram: a diagram with axes of temperature and composition, describing the different phases that occur in an alloy at equilibrium with changing composition or temperature.
Piling: hammering several strips of metal together.
Porosity: gas porosity is the formation of bubbles within the casting that are trapped during cooling. This occurs because most liquid materials can hold a large amount of dissolved gas, but the solid form of the same material cannot, so the gas forms bubbles within the material as it cools down.
Quaternary alloy: an alloy containing four principal elements apart from accidental impurities.
Quenching: the act of quickly cooling a metal or alloy by plunging it into cold water or oil.
Quenched structures: usually nonequilibrium structures or phases that have been made metastable in an alloy by quenching in water or oil. The most common phase indicating quenching is martensite in steels.
Recrystallised grains: new set of grains that nucleate and grow until the original grains (deformed by cold working) have been entirely consumed.
Refining process: purifying an impure metal. The final material is usually identical chemically to the original one, but is purer.
Relative standard deviation: absolute value of the coefficient of variation. It is often expressed as a percentage. A similar term that is sometimes used is the relative variance which is the square of the coefficient of variation.
Rolling: process in which a piece of metal is passed through a pair of rollers, consequently thinning out and becoming elongated.
Scrap metal: metal that has been abandoned and now serves as stock metal. Unlike waste, scrap has significant monetary value, as the metal can be reused.
Slag inclusions: a glassy phase or mixture of phases (often wüstite-FeO dendrites and fayalite (Fe2SiO4) in a glassy matrix) usually found in ancient or historic wrought iron or steel. They may be incorporated in Fe-alloys as a result of oxidised metal during hot forging (secondary smithing) or while refining the bloom (primary smithing), when no complete expulsion of slag can be achieved.
Secondary element: a minor element of an alloy with a concentration between 10 and 1 mass%.
Secondary re-deposited copper: during long term corrosion electrochemical processes can deplete an Sn-bronze and dissolve and re-deposit Cu.
Smelt: is a form of extractive metallurgy. Its main use is to produce a metal from its ore. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements such as gases or slag and leaving just the metal behind. The reducing agent is commonly a source of carbon such as coke, or (in earlier times) charcoal. The C (or carbon monoxide derived from it) removes oxygen from the ore, leaving behind elemental metal.
Soft steel: equivalent to mild steel (contains 0.16–0.29 mass% C).
Solid solution: solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase. This often happens when the two elements involved (generally metals) are close together on the periodic table.
Stainless steel: steel containing Cr (and Ni) which makes it resistant to corrosion.
Steatite: A hard structural constituent of cast iron consisting of the eutectic of Feα and Fe phosphide (Fe3P); composition of the eutectic is 10.2 mass% P and 89.8 mass% Fe.
Strain or slip lines: straight line(s) that appear in grains of FCC metals after cold work.
Telluric iron: iron found in a metallic form in nature. Telluric iron has only one major deposit in the world (located in Greenland). Like meteoric iron, it contains a significant amount of Ni (3 mass% which is too low for meteorites) and Widmanstätten structures.
Tempering: process usually applied to quench-hardened steels in which some of the hardness is removed by heating at moderate temperatures, from 100 to 600°C, depending on the type of tempering required.
Thomas steel: produced by the Thomas process, a refining process for cast iron, used between 1880 and 1970. The Thomas converter was able to remove P in the fining smelting. Typically Thomas steel has a high Mn content and contains nitrides.
Tin bronze: a bronze containing only Sn as major element.
Twins (twinned or twinning): after repeated cold working and annealing of FCC metals straight and often twinned line(s) appear within the grains.
Welding: joining two metal surfaces together by heating until they melt and flow together.
Welding seam: line left by welding progressively, starting at one end. Butt welding, on the other hand, typically welds the entire joint at once.
Widmanstätten structures: in meteorites, fine interleaving of kamacite and taenite (both are Fe-Ni phases) bands or ribbons called lamellæ. Commonly a fine-grained mixture of kamacite and taenite called plessite can be found in gaps between the lamellæ; also a frequently encountered structure in forged steel showing ferritic needles in pearlite.
Wrought iron: Fe that has been forged including slag.
Anaerobic and aerobic conditions: environment without and with dissolved oxygen.
Brochantite: green Cu-sulphate CuSO4,3Cu(OH)2 often found on outdoor copper alloys such as sculptures or roofs.
Chalcopyrite: CuFeS2, a corrosion product formed on Cu alloys buried in anaerobic conditions and in soils containing both sulphato-reducive bacteria and Fe cations; main component of lake sediments patina.
Corrosion crust: all corrosion layers formed on a metal surface.
Covelline: CuS, a corrosion product formed on Cu alloys buried in anaerobic conditions and in soils containing sulphato-reducive bacteria.
Crack: large fissure that forms in a corroded metal artefact within the remaining metal or the corrosion crust.
Cuprite: Cu2O, the first corrosion layer that forms on copper alloys exposed to a clean atmosphere. Often corresponds to the limit of the original surface.
Dehydration: loss of water.
Dirt: mixture of stones, sand, clays particles and humus.
Fissures: a long narrow opening.
Ghost structure: remains of the original metal structure in corrosion products.
Interdendritic corrosion: preferential corrosion of the metal immediately surrounding dendrites in unworked or slightly worked alloys caused by composition gradients.
Intergranular corrosion: corrosion along the grain boundaries.
Limit of the original surface: on excavated ancient metals, the original surface (OS) is the surface of the metal when abandoned. It has an external limit: the limit of the OS. The limit of the OS on historic metals would correspond to their surface after the last conservation intervention.
Localised corrosion: corrosion in which there is intense attack at localized sites on the surface of a component whilst the rest of the surface corrodes at a much lower rate.
Malachite: CuCO3,Cu(OH)2, a corrosion product formed on Cu alloys buried in aerobic conditions; main component of terrestrial corrosion crust.
Markers of the limit of the OS: species characteristic of the strata above the limit of the OS (superior markers), below the limit of the OS (inferior markers) or indicating the limit of the OS (corresponding markers).
Patina: subjective term for a uniform, protective corrosion crust that preserves the general shape of a metal artefact. The limit of the original surface is usually preserved within a patina.
Pitting: is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving force for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion.
Stratigraphy: assemblage of strata that describes a corrosion form.
Tenorite: CuO, a corrosion product formed on Cu alloys exposed to high temperatures.
Transgranular corrosion: corrosion through the grains.