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This is very comprehensive, so you may want to scroll down for various headings of interest.

1) Overview

2) THE ISSUING AUTHORITY

3) THE METALS

4) METAL SOURCES

.5) REFINING THE METAL AND PRODUCING THE BLANKS

6) MAKING THE DIES

7) STRIKING THE COINS

8) LIFE OF A COIN AFTER MINTING

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1) Overview

In a coin, especially an ancient coin, form follows function; its function as legal currency controls many elements of both its production and its design. To produce a coin a legitimate authority stamps a disk or lump of metal of a certain purity and weight on one or, more usually, both sides with designs ("types") and sometimes inscriptions ("legends"). The types and legends identify the authority and certify that the piece of metal is legal currency, at least within the area governed by that authority. The requirements then to produce a coin are: an authority to issue and guarantee the coin's worth as money, possession of the bullion or metal from which the coin will be made, the ability to refine the metal to the desired purity or fineness, and the tools and techniques to fabricate the coin from the metal. Almost all early coins were struck by hand, and the striking process changed little from the beginning of coinage until the sixteenth century, when coins began to be machine-milled. Striking coins by hand involved three stages: making a blank (or "flan"), the plain lump or disk of metal which when impressed with the types becomes the coin; making the dies, the stamps used to transfer the types onto the flan; and striking the coin.

2) THE ISSUING AUTHORITY
Ancient and Byzantine coins were almost always issued by the state, either in the name of the state itself or in the name of the ruler or some official designated by the state. In the Greek period, when the city-state was the main political unit, it was the city that issued coins. In Hellenistic times most coins were issued by the rulers of the kingdoms that were created after the death of Alexander the Great. In Roman imperial times most were issued by the empire, by the emperor himself or jointly by the emperor and the Roman Senate, although the Senate's consent was nominal. The Hellenistic kingdoms and Rome sometimes granted individual cities under their power the right to mint their own coins, although only coins of lesser value.

The issuer determined the weight, type, and purity of the metal of the coins and also the types and legends stamped on them. It is likely that for Roman imperial issues the types would have been approved by the emperor himself. The state also would have specified at least a nominal value for the coin. The mints themselves were usually operated directly by the state, employing mostly slave labor. The state also retained the rights to any minerals in its own territories, although the actual mining of the ores may have been contracted or leased out.

3) THE METALS
Ancient coins were made from gold, silver, electrum, and copper and its alloys, bronze or brass. The earliest coins, minted in Asia Minor in the mid- to late seventh century B.C., were of naturally-occurring electrum, an alloy of gold and at least 20 per cent silver. They were consistent in weight, implying that they were intended to have a set value, yet their value as bullion varied greatly, since coins of the same weight possessed different ratios of the more precious gold and the less precious silver. These early electrum coins were minted for only about fifty years, and by the middle of the sixth century they were replaced by coins of silver. Gold coins did not become common until the time of Philip II, the father of Alexander the Great.

Coins of gold and silver are said to be coins of intrinsic value, since their worth usually closely approximated the value of the bullion making up the coin. The weight of individual coins of the same denomination was, therefore, closely monitored. Not all states followed the same weight standard, but each city-state, especially the more important mints such as Athens, adhered quite strictly to its own standard in minting its coins; the standard for the coin was 17.20 g.). As time passed, however, most weight standards were reduced.

The fineness or purity of the metal used for gold and silver coinages was also closely monitored. Throughout Greek and Roman times, gold coins were consistently of very high purity, usually more than 95 per cent pure gold. Silver coins were of an equally high purity until the time of the Roman emperor Nero, who lowered the silver content, but only to about 90 per cent. By late Imperial times, however, some "silver" coins contained very little silver, at times as low as 2.5 per cent.

In most cases, however, coins of precious metal, certainly those of silver, were somewhat overvalued, somewhat lighter than bullion of equal value would have been. Some overvaluation is to be expected simply to cover the cost of the minting, but it is also clear that in some cases the state minted coins for the purpose of making a profit. The overvaluation of the Athenian drachm was about 5 per cent; it may have been higher in other states since cities such as Athens that had their own mineral sources could better afford to keep the overvaluation low.

Coins of copper and its alloys, not common until the later fourth century B.C., possessed a value that bore little relation to the value of the metal, and thus, like most modern coins, they are called token or fiduciary coins. These coins were highly overvalued in terms of their metal content and were therefore much more profitable for the state to produce. Consequently, less care was given to the weight of individual copper coins and to the purity of the metal or alloy used.

For the token coinages, the Greeks used mainly bronze, copper alloyed with tin, or simply copper. The Romans used a yellowish alloy of copper and zinc, a type of brass called orichalcum, for the higher token denominations and the redder copper for the two smallest denominations. Both Greeks and Romans sometimes added lead or used lead bronze, probably because lead made the blanks somewhat softer and easier to strike. Numismatists label all copper-alloy coins as bronze (AE).

4) METAL SOURCES
Much more so than today, whether or not a city minted coins depended upon the supply of bullion. Not all cities or states minted coins, and sometimes it was the availability of bullion itself that led a city to issue coins. The supply of bullion could also affect the value of silver or gold coins.

One of the main sources of bullion was mining or collecting surface deposits. The natural electrum used in the earliest coins was found among river gravel deposits in Lydia (western Turkey), the region of the states that issued them. The few later electrum coins, for example those from Carthage, were not natural electrum, but man-made alloys. Of the three Greek cities that first issued silver coins -- Aegina, Corinth, and Athens -- only Athens had a source within its territory, the silver mines of Lavrion. The discovery of an especially rich silver vein there c. 500 B.C. made possible the minting of the famous Athenian "owls". Silver was also mined in northern Greece, in Thrace and Macedonia, and on the Aegean islands of Thasos and, until its mines were flooded in the late sixth century B.C., Siphnos. These sources were used both by local cities and by the many cities with no mines of their own, who purchased the silver. Greeks would also have had access to silver sources in Asia Minor and in Spain, the source of most of the silver used by South Italian and Sicilian cities and by Carthage.

Gold sources existed in all these regions as well, yet they were rarely exploited until the Hellenistic period. In Hellenistic times not only were rich Macedonian sources exploited, but as Alexander expanded his rule eastward, more sources of both gold and silver became available throughout the Middle East and as far away as India and even Siberia. A prospector even accompanied Alexander expressly to look for new sources. Egypt under the Ptolemies was in the unusual position, with the rich gold mines of Nubia (southern Egypt/Sudan) at its disposal, of having more gold than silver, and the Ptolemies based their coinage on gold rather than on both gold and silver, as was most common at the time. The Carthaginians continued to have access to Spanish sources, but they and the Kyrenaicans may have also obtained gold from the "Gold Coast" of sub-Saharan West Africa, either with ships sailing through Gibraltar or by caravan across the Sahara. Many of the Middle Eastern sources were at times closed to the Romans. They obtained much of their gold and silver from the rich sources in Spain, but they also had access to mines in Gaul, Dalmatia, Dacia (in the Carpathian mountains), Britain, the Near East, and Africa.

Of the less precious metals, copper was relatively easily available to both Greeks and Romans from important sources on the Greek mainland, on Cyprus, in Spain, and in Britain. Tin, however, was rare in the eastern Mediterranean area. The main source for the Greeks seems to have been Cornwall in England; some also came from Brittany, Spain, and perhaps from the Middle East. Rome obtained most of its tin from increased exploitation of Spanish mines. Zinc and lead were not difficult to find; various sources were located in Europe, Britain, and Asia Minor.

Metal from freshly mined ore was not the only source of bullion, even for those states possessing their own mines. Booty taken in war, payments made to governments by other states, accumulated wealth stored in a state's treasury, and existing coinage, usually that of foreign states, were other sources. The war-time need for such secondary sources is well documented at Athens, where emergency issues were minted from treasure stored on the Acropolis. In 407/6 B.C., near the end of the Peloponnesian War, Athens' enemy Sparta occupied Attica, rendering the Lavrion silver sources inaccessible. To meet its military expenses, Athens melted down seven gold statues of Nike to mint 84,000 staters (1 gold stater = 6 silver tetradrachms). One hundred years later, gold from the shield of the chryselephantine statue of Athena in the Parthenon was used for coinage to pay foreign mercenaries. Part of the gold for the coinages of Alexander and his successors came from the vast wealth of defeated Persian rulers. Roman emperors seized much booty during their military exploits; Trajan's defeat of the Dacians flooded Rome with their gold. Often, conquered states were forced to pay duty or fines to the victors. Whether in the form of coin or uncoined metal, these payments could be melted down and reminted, or sometimes the coins, if of appropriate weight, would simply be restruck, the new types impressed over the old. Foreign coins came into the states' treasuries in the normal course of trade. Some of these would be kept as "foreign reserves," but many could be used to mint new coins.

.5) REFINING THE METAL AND PRODUCING THE BLANKS
Once bullion had been obtained, the next step was to smelt and refine the metal to the desired purity or fineness, and then to make blanks of appropriate weight. The Greeks had been working metal long before the first coins were struck, and at least by the end of the sixth century they were able to extract metals from ores by smelting, to determine the purity of the refined product, and to make alloys or separate alloys into their constituent parts. Extensive remains of ore washeries and furnaces have been found in the Lavrion mining area, and ancient literary sources describe the processes. We know from the precious coins themselves that both Greeks and Romans were able to obtain a high degree of fineness of metal and to adjust the fineness to the desired level. When debasement began to occur, in some regions in the first century B.C., it was well controlled. Ancient craftsmen were also skilled in producing the various alloys used in the token coinages and knew the advantages of adding components such as lead.

To produce blanks of appropriate weight, molten metal was poured into open or two-part closed clay moulds. Experimentation has shown that, with practice, pouring into open moulds or even simply onto a flat surface can be controlled accurately enough to produce blanks within acceptable weight tolerances. Some scholars, however, disagree that such methods would have been used to produce flans for gold or silver coins, and it has been suggested that metal beads or granules of the correct weight were placed in a mould, which was then put into a furnace to melt the granules.

Flans of early coins tended to be spherical or lentoid in shape, and the coins made from them were often quite irregular, preserving the shape of the lentoid flan, flattened by the striking. In all periods the weight of the coin mattered more than its shape or size. In fifth-century B.C. Sicily, evidence for the use of two-part spherical moulds is preserved on the coins themselves. The flan made from this type of mould would have looked a bit like an unshelled walnut, with a ridge running around its middle produced by metal flowing into the joint where the two halves of the mould joined. When a coin was struck from such a flan, remains of the ridge appear as two small projections on opposite sides of the edge of the coin. In Hellenistic times flatter, disk-shaped flans were cast, and this continued to be the normal shape, at least for gold and silver coins. The result was thinner coins of a slightly larger diameter.

It is most probable that silver and gold blanks were normally cast in individual moulds. Yet often the blanks for bronze coins, and sometimes those for silver, were cast en chapelet, that is, using open or closed moulds in which a number of mould hollows were connected by channels. Clear evidence for this method exists; the runners that connected the flans were not always completely removed.

Another method used to produce bronze blanks was to pour out a specific weight of bronze in a solid rod or sheet and then to divide it up into a certain number of blanks, either by sawing or chiselling a segment off the rod, or by cutting a section from the sheet. Unstruck blanks cut from a rod were found in the Athenian Agora, from a building probably used as the mint for early Roman bronze coins. And some later Roman sestertii and some Byzantine coins are slightly square in shape, as if they were squares cut from a sheet and then hammered into a more circular shape.

One further step often required before the flan could be struck would be to remove any impurities that may have risen to the top of the flan owing to oxidation during open casting. The flan could have been washed in some form of organic acid or pickle; in some cases the impurities seem to have been scraped off.

6) MAKING THE DIES
Metal dies were used to stamp the types into the flans. Relatively few ancient dies have been found, and many of these were probably forgeries, since official dies were often destroyed so that they could not be used illicitly when they became too worn or when a change in types demanded that new dies be cut. Yet enough evidence exists from ancient and medieval dies, from the coins themselves, and from modern experiments, to allow us to describe dies with some confidence.

Although iron is harder than bronze, hardened bronze is hard enough to strike even bronze coins, and evidence indicates that bronze containing a relatively high percentage of tin was the preferred material for dies. Iron dies were sometimes used, however; marks on some Syracusan coins indicate that they were struck with rusty dies, and a sixth-century A.D. iron die is preserved.

Since with rare exceptions the images on ancient coins are in relief, the images on the dies are inset and reversed, the negative and mirror images of what is depicted on the coins. As difficult as this may seem to do by hand with little or no magnification, the Greeks had a long history of cutting stone seals, which required very similar technique and artistry. The tools used to engrave the dies included iron or perhaps even steel burins and small chisels to remove metal from the face of the die, punches to impress an image into the face of the die, and perhaps simple bow drills, tipped with corundum or other abrasive, to drill into the die face.

At times great artistry went into the die-cutting; in some instances dies were even signed by their artists, as was the case with the remarkable coins of Classical Sicily. Dies with simple types in low relief could be cut in less than an hour, yet the job could be quite time-consuming; it took a nineteenth-century counterfeiter 18 hours to copy the die for a coin from Akragas.

In striking a coin two dies, an obverse and a reverse, were usually employed. The obverse or lower die would have been set into an anvil, often a block of wood. The upper, reverse die was loose, and could take a variety of different forms. The type could be cut directly into the end of a short rod, cylinder, or pyramidal piece of metal, but most often the die proper was simply a short segment or disk of bronze inserted into a punch or collar made of iron. The whole punch, with the reverse die attached, was probably only about two to three inches long.

In ancient coins the lower or obverse die was almost always used to stamp the principal face of the coin, usually depicting the head of a deity or ruler. It was preferable to carve the deeper and more intricate image into the lower die, since it was placed within an anvil and was therefore better protected, wore down less quickly, and suffered less damage than the upper die, which received direct hammer blows during the striking. It should be noted that in general use, the term "obverse" usually designates the principal side of the coin, our "heads," regardless of whether it was made with the lower die.

The number of coins that could be struck from a die before it had to be replaced varied considerably, owing to a number of factors: metal composiiton, size of coin, and depth of relief. Smaller dies and dies with shallower relief lasted longer. Modern experiments suggest that an obverse die could strike about 15,000 acceptable coins, a reverse die only about half as many. Often, however, more than two reverses were used with an obverse die, since dies were often replaced before they wore out. Ancient dies were also often partially recut or altered, both to repair small flaws or cracks that might develop in the die face and to change or add inscriptions. Sometimes damaged dies continued in use.

The lifespan of dies was dependent on the number of coins struck. Dies at smaller mints were often used for three to five years. In the busy mint of Hellenistic Athens, an obverse lasted for three to five months. Andduring some peak periods of minting in Roman times, a die might have lasted only 12 hours.

On the earliest coins an unadorned punch was used to press the flan into the image of the obverse die. The punch, much smaller than the blank, left a square or rectangular impression in the reverse of the coin. Soon the punch was decorated with a simple symbol, and by the end of the sixth century B.C. a true reverse die was usually attached to the punch. Yet it was often still smaller than the blank, so that the relief design on the reverse was set within a depression the shape of the reverse die; these are called incuse reverses. In time the reverse die grew in diameter to approximate the size of the flan and obverse die, and although the reverses of most ancient coins are always slightly concave, by Hellenistic and Roman times the concavity is hardly noticeable, and the form of the reverse appears almost identical to that of the obverse.

In many cases one person could manage the whole striking process alone, first placing the flan on the lower die and then, holding the upper die in place with one hand, wielding the hammer with the other. In this way a modern experimenter was able to strike 100 coins an hour, including casting the blanks. Yet more often, especially in large mints, three or four people were involved. Using tongs, one person would bring the flan from the furnace, another person or possibly two would hold the punch in place by hand or with tongs, a third would wield the hammer, and a fourth would remove the struck coin. Evidence for this comes both from coins and from Latin inscriptions that list the workers in the Roman mint. Some Roman coins were misstruck in ways that indicate not only that three or more people were involved but also that in some instances the rate of production was very rapid, perhaps as much as one coin every three seconds. And for some of the Roman bronze issues of many thousands of coins, not only would three or four people be working at an anvil, but more than one anvil would have been active at the same time.

Greek coins, produced in smaller quantities, also often show some sloppiness in manufacture, even when carefully cut dies were employed. The coin may be struck off-center or may not receive the complete image of the die because the flan was placed off-center. The flan might move slightly between hammer strokes, causing a slight double-strike. The reverse image may be of uneven depth because the punch was not hit straight on.

The relative orientation or alignment of the obverse and reverse images on ancient coins varied considerably. This is easy to understand, since the two dies were not connected to each other and the punch could be rotated freely. In early coins especially, the relative position of the dies seems to have been fairly random. In Hellenistic and Roman times, greater concern was given to die alignment, some mints preferring that both faces be upright, some that one face be inverted, as on modern U.S. coins. Some dies may have had pegs or notches to help guide the minters in orienting the punch, but dies were not hinged until late Roman times, and often the two faces are slightly out of alignment, not perfectly upright or perfectly inverted, even when a certain orientation was clearly preferred.

8) LIFE OF A COIN AFTER MINTING
What happened to a coin after it was issued depended to a great extent on its denomination. Having only fiduciary or token value, bronze coins were unlikely to travel far from where they were minted. These smaller denominations served the everyday purposes of most people, who primarily used them in the market place. Coins of silver or gold, on the other hand, were more likely to have been used in international trade or for various payments to or by the state -- to pay taxes or military expenses.

Silver and bronze but almost never gold coins sometimes had small marks, usually symbols or monograms, punched into them after minting. Called punchmarks or countermarks, these were made both by merchants or private individuals and by states. Countermarking of silver coins, most common in the Hellenistic period, was usually done by a state to show that foreign coins could be used as legal tender in its territory. In some states, such as Hellenistic Pergamon in Asia Minor, all foreign coins had to be countermarked. The state could thus maintain a monopoly on coinage and make a profit from countermarking fees. But countermarks are relatively rare; more often states accepted foreign coinage as legal tender without marking it, especially in the case of well-known and respected issues such as Athenian "owls". Or the state or its merchants kept some foreign coins to use in their commercial or other dealings with the other state.

Unlike silver coins, bronze coins were countermarked by the states that had issued them. A state might demonitize a bronze issue, usually to raise money by issuing new coins, or people holding old coins could get them countermarked for a fee. Countermarking was common in the first century A.D. when, owing to a shortage of bronze coins, even very worn coins as much as forty years old were countermarked with the initials or monogram of the emperor or issuing authority.

Occasionally a Greek silver coin is found with a person's name scratched on it. This might have been written to ensure that the person, having left his coin on deposit for some reason, would receive the same coin back, and not another one that was more worn and thus lighter. Another form of graffiti found on coins is the initial of a deity to whom the coin had been dedicated.

In general, if a coin lost weight through wear to the point that it would not be accepted, the loss had to be borne by the owner of the coin; the state would not replace it. Some states did have laws, however, to help guarantee against forgeries. In fourth-century B.C. Athens, a person could bring suspect coins to official testers on duty in the Agora, the market place, and in Peiraeius, the port. Coins found to be silver-plated forgeries were defaced with deep chisel cuts and dedicated to the Mother of the Gods.

What ultimately happened to a coin also depended to a great deal on its denomination. Most bronze coins extant today probably had been lost by their former owners; they are the coins most frequently found in archaeological excavations or as stray surface finds. Of the 14,000 Athenian coins found in the excavations of the Athenian Agora, more than 99 per cent were bronzes, and of the 100,000 coins of all types found there, the great majority were bronzes. Silver and gold coins were valuable enough that, if lost, their owners would take the time to try to find them. They are more likely to be found in hoards, intentionally buried or perhaps hidden in a cave, deposited by their owners for safe-keeping, either in emergencies or as a normal safe-keeping procedure; there were no ancient banks in our sense of the word. Hoards are usually found by chance and not during archaeological excavations. Most hoards are dispersed and sold before they can be properly studied or recorded; even their find spots may not be known.