User:Curtius/Ancient Technology of Coinage

The production of coins in the ancient world required a number of technologies be in place. These are discussed below.

Metals used and their sources

Gold

Gold is found in veins in quartz rock, pyrites, and arseno-pyrites. The weathering of these materials can lead to the gold being washed away by streams, usually being deposited in alluvial gravels in these rivers (placer deposits). Placer gold can be easily extracted via panning or the use of greasy sheepskins placed in the river or later is sluices; this is the probable origin of the legend of Jason and the Golden Fleece.

The most famous source of alluvial gold in the ancient world was Sardis which had placer deposits in the rivers Pactolus and Hermus (the modern Gediz River) nearby and also in the regions of Magnesia and Nymphaea, within a day's journey. These were the source of King Croesus's wealth. Mainland Greece had small amounts of gold in Macedon/Thrace. Production was very significantly increased when Philip II of Macedon took control of a number sites, especially Potidaea near Mt. Pangeaum, which he renamed Philippi. Diodorus wrote that the revenue from this source alone was 1000 talents per year.

Direct mining of veins of gold is also attested; at Dolaucothi, North Wales extensive mining is seen from Roman times with some evidence of prehistoric mining as well. Diodorus also described mining of gold in veins of quartz by prisoners in Egypt.

Electrum

Pliny knew that silver appears in gold ores naturally and Herodotus used the term "white gold" to refer to the metal produced by smelting such ores to distinguish between it and refined ("cooked") gold. When the concentration of gold and silver are manipulated to some standard, the mixture can be called electrum.

Silver

In addition to the silver found in gold ores, silver is also found in argentiferous lead ores. The famous Athenian-controlled mines at Laurion are examples of this. Silver was also found in Spain, Macedonia/Thrace, Siphnos, Stageira, Melos, Lesbos and Sardinia in classical times. It has proven possible to identify the site of the ore production of much archaic greek silver coinage by looking at the lead isotopes found in the trace amount of lead remaining in these coins and by examining the gold, bismuth and tin content. This showed that most archaic coins were produced from the Laurion and Siphnos mines with some additional coinage coming from a third, as yet unidentified site. This type of analysis is no longer possible for later coinages as they are often produced by re-melting of earlier coinages.

The silver mining of Spain was greatly increased by the Carthaginians under Hamilcar Barca. Further increases in output were made by the Romans at New Carthage, Tuditania, Ilipa, Castulo and Rio Tinto.

Bronze

Bronze is an alloy of copper and tin. Copper was mined by 8th millennium B.C. Malachite and azurite are strikingly coloured ores (green and blue respectively) and this, along with the plant species that grow abundantly in copper enriched soils may have been an aid in prehistoric "prospecting". Bronze is harder than copper and tin lowers the melting point, acting as a degassing agent so that castings tend to be more successful. A crucible containing tin from the Göltepe site in Anatolia has been dated to the late fifth to early third millennium B.C. After about 2000 BC, lead was sometimes also added; this increased the fluidity of the alloy and made casting easier.

Copper was mined at Chalkis in Greece, Macedonia and Cyprus. In Roman times, copper mining in Spain was greatly expanded from very low earlier levels. Tin was mined in Brittany and the "Casserides" (tin islands), probably Cornwall and other sites from ca 500 B.C. Lead was mined at Laurion and on Sardinia and Ceos by the Greeks. The Romans also mined lead in Spain at Baetica (the Salutariensian and Antonian mines in this region were rented out for 255,000 denarii per year), Cantabria, New Carthage and especially Linares, and in Sicily at Iglesias. Under the Romans, lead production was very large, evidence of lead pollution from Roman industrial activities has been observed in the ice of Greenland's glaciers.

Orichalcum (brass)

Brass is an alloy of copper and zinc. It, like bronze is harder than copper but has a colour more similar to gold. Brass was first produced in Assyria in the late second millennium B.C. Brass coinage with 20% zinc first appeared in Bythinia and Phrygia during the first century B.C. Zinc was mined in Laurion. The emperor Augustus introduced orichalcum coinage in 23 B.C.

Mining & Metallurgy

Mining

The use of shaft mining, horizontal galleries with supported roofs and ventilation techniques dates to the bronze age. Mining proceeded using iron hammers, primarily by slaves - Xenophon describes how individuals owned a thousand slaves in the mines and leased them out for a fixed daily rate. The life of a miner was harsh - "Indeed on account of the magnitude of suffering, death to them is preferable to life." They often did not have long to wait, even with the ventilation shafts, the use of extension chimneys on shafts or air heating within shafts, and the use of linen cloth fans to circulate the air, miners often died from fumes. Others died from roof collapse or rock falls even though roofs were supported by wooden beams or arches. Sometimes the losses of slaves were so large as to make an entire mine uneconomic.

The actual work was done with heat and acid (fires and vinegar), battering rams weighing up to 150 pounds, iron hammers, and wedges. Water was removed from mine shafts via Archimedean screws and water wheels. In the Rio Tinto mines, at least eight levels of wheels are known, each wheel raising the water 3 to 4 meters.

Mineral Separation

When alluvial deposits were exploited, the separation of the mineral from the burden occurs as part of the panning/sluicing operations; the same process was often applied to the ores mined from other deposits. In this case it's necessary at first to crush and sieve the ore in water. The crushing of ore to a powder was performed first by heavy iron pestles in stone mortars followed by grinding mills with a vertical axis by the Roman times. The Laurion mines used a system in which the powdered ore was spread over a large, plastered, slightly inclined table surrounded by water channels. Water played over this (and recycled!) could be used to partially separate the metal from the ore. In the Roman period, alluvial deposits were excavated using large volumes of water - as much as 34 million litres per day provided by multiple aqueducts at a single site. The water could be delivered as a continuous stream or in waves to help remove unwanted components of the ore.

Refining

The separation of base and precious metals was done by a process called cupellation. The metal to be purified was mixed with lead, heated to 1100C under a blast of air. In those conditions, lead oxidises to PbO (called litharge) and absorbs all the base metals, leaving gold and silver as a separable mass.

Gold and silver could be separated ("parted") by a process called salt cementation. In ancient times cementation required that gold be beaten into thin sheets and placed in a coarse earthenware container with salt (sodium chloride), heated between 600 and 800C for a few days. On heating, the salt evolves chlorine gas and HCl. The latter reacts with water vapour from the wood fire and ferric oxides found in the earthenware container to produce FeCl. The various chlorine compounds react with the silver, particularly along grain boundaries in the metal to produce AgCl which is volatile. The silver in the bulk of the grain diffuses to the boundaries and also reacts, the gold remains. The silver contaminates the container and the furnace from which it can be recovered by cupellation. The parting process is still the standard assay process; when the result of parting is no decrease in the weight of gold, the gold is pure.

Excavations and their analysis have identified a gold refining operation There is much direct evidence including fragments of gold leaf, earthenware shards with traces of gold drops and characteristic dis-coloration due to heating and silver chloride contamination, cupellation sites used in the silver recovery process, litharge from these sites complete with the impression of the resulting button of purified silver.

The parting process was used at least as early as the third millenium BC at Ur to remove silver from the surface layer of gold-silver alloyed objects. This made the object golden on the surface while preserving its weight. The process of separating the two does not seem to have been commonly done before the introduction of gold coinage and it has been shown that there are marked differences in the composition of gold objects made by those who produced a gold coinage and those who did not.

The mercury amalgamation process was also used in ancient times. This come into use after the method of extracting mercury from cinnabar ore mentioned by Theophrastus was developed in Spain around the end of the first century BC.

Assaying

There were three main methods available for assaying precious metals in antiquity.

• The measurement of specific gravity is famously ascribed to Archimedes. This technique is practical for large objects, but surface tension effects make it extremely inaccurate for smaller objects.
• The term "Fire assay" refers to re-refining the material and comparing the refined weight with the original. This technique is accurate (especially if repeated until the weight no longer changes) but destructive.
• Touchstones were stones with uniform, dense, matte surfaces; the gold was rubbed on them and the streak was compared to streaks created from materials of known composition. Mt Tmolus, from which the rivers Pactolus and Hermus ran, was a source of such stones.

Minting

The minting process for ancient coinage was as follows

• A blank was produced of the appropriate weight of the chosen metal.
• This blank was heated and placed between two dies containing the negative of the impression to be created.
• The upper (reverse) die was struck with a hammer and the metal was stamped by it and the lower (obverse) die resting on an anvil.

The operation of the mint thus required three separate products, dies, blanks, and coins.

Die Production

• Die Engraving:
• Magnifying glasses in the Celator...
• gem engraving
• Use of hubs:

Evidence

Minting Errors

• Brockages:

Casting

Some ancient coins were cast rather than minted. In this case

Quality Control

• "Lydian electrum royal coinage has been shown to be of very consistent composition."
• Mint Marks
• Control Marks
• Gouging:
• Serration #249

Gilding, Plating & Fourees

• Pászthory identifies both an electrum plated lead-core and an electrum plated silver core coin.

Modern Evidence

• Lead analysis:
  • Etruscan copper
  • ,
• metallography
• Platinum-group inclusions in Celtic coinages indicate contact with the Mediterranean.
• Celtic Gold Coin Production techniques.
• electrum and inclusions

See also

• Roman Republic
• Roman currency
• Roman provincial coins

References

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