3.          Minting Methods of Early Coinage

 

Early metal coinage began independently with three of the four Old World River Valley Civilizations concurrently about 2500 years ago. These four cultures were the Egyptians along the Nile River, the Mesopotamians along the Tigris and Euphrates Rivers, the Indus Valley peoples along the Indus and Ganges Rivers, and the Chou Dynasty Chinese along the Yangzi  (Yellow) River. The Egyptians did not have a known coinage during the ages of the Pharaohs, possibly because they were a civilization whose people were acknowledged slaves to the Pharaohs when coinage had its beginnings. Taxes paid to the Pharaoh were in goods and trade with foreigners was by goods bartering. The other three developed a coinage as they were more so a merchant peoples and needed an exchange system past one-to-one barter of goods. The three each had a major difference in their early money methods of manufacture.

A.         Mesopotamia

 

C.         Early Yangzi (Chou Dynasty China)

In Mesopotamia, the 5th century BC city-state of Lydia (in present day western Turkey) was the recognized first place to invent the idea of coins as a medium of exchange. The idea quickly spread throughout the known region among the city-states. These ancient cities had standards or emblems by which they were known. These standards were stamped or hammered into the coins so their origins could be recognized. Lydia had a lion facing a bull Aegina a turtle, Ephesus a bee and Corinthia used Pegasus for its emblem to name just a few.

Coins were small and portable. Coin producers used weight standards for different denominations. These coins were more convenient for trade than the bulky system of barter where the actual goods where carried about and exchanged. Now a merchant could sell his goods, go elsewhere and there buy what he choose with this currency exchange system. Silver, electrum (naturally occurring gold mixed with silver), gold, copper and bronze were used for coins.

Their first coins showed tong or pincer marks on their reverses where the small hot glob of metal was picked up, this tool also being the punch that was hammered. The metal to be used was placed on a carved out die, which had the obverse image carved into it; the cooling metal was hammered once to take on the image on the die. Later they refined this method and had engraved images on this punch tool as well thus producing coinage with two engraved images for an obverse and a reverse. Their skill quickly became so refined, the smallest of coins 1/4 inch across (0.6 cm) could have a detailed image of an animal or person. The earliest of portraits are preserved on their coins, even showing us today their dress and hairstyles. Greek coins with the head of Athena (goddess for Athens) on the front and an owl on the back, “Owl coins”, was such an example.

For Mesopotamia, the coins were produced individually and this was the primary method employed.

The exception and the oddest one from the ancient Greek world was from Olbia, it was in the shape of a dolphin, which was cast in a “money-tree” (note: they never had a tail).

B.         Indus Valley

In the Indus valley the people there separately came across the idea of coinage, as well as the far-east early Yangzi peoples, about the same time as the Mesopotamian peoples.

The Indus peoples refined silver and bronze into small flat pancake shapes, roughly 1/8th to 1/4 inch thick (.3 to .6 cm) and several inches round. Upon this they hammered distinctive local symbols of their city or region, which were often images of crop grains to livestock and game they identified with. A city or region may have had as many as 9 identifying symbols they would use from the myriad that the Indus people employed. The sheets were then chiseled into

small finger lengths, or thumbnail size pieces, retaining only a portion of the images on any one sheet. The chiseling was part way and then the portions were snapped apart. Thus the coinage often retained a slight dish-shape because of the extensive hammering to the original large sheet.

The early Yangzi peoples of Chou Dynasty China had yet another approach. They used the casting method, using primarily bronze. They poured the hot metal between two sides of a mold creating a “money tree”, in which the pieces were then broken off this tree, not unlike parts of an unassembled plastic model still on its molding tree as it first comes out of its box. Older cast coins may still show the spurs where they were broken off.

 

Identifying characters of city names, issuing authorities or mints, currency value, emperor reign titles and their reigning year were dominantly used by the Chinese. No figures or images were found on the early coinage though some appeared infrequently later. The early coinage took the representative shapes of early bartering items, imitating the shapes of spade tilling tools, knives, and an earlier exchange form for shell money that led to  round coins.

Shell money was an earlier form of recognized exchange of valuables for the Pacific Ocean peoples. Cowry shell were valued by the early Yangzi culture and influenced their coinage much. They also carved bone, stone and jade, cast bronze and baked clay in the shape of cowry shells. Shell money was almost always strung through a natural or created hole in long strings of hundreds of pieces. This idea of stringing prevailed through the whole history of their cast dynastic coinage, from the earliest of their coinage to the last Emperor. This idea of stringing was also different than the other two early coin producing civilizations because the Chinese used less the idea of the individual coin but rather one hundred tied together for exchange purposes. Early large pieces of spades and knives were likely singly 

handled yet carried on a string; later small spades had no holes and were probably  carried in a sachet. But later round coinage was certainly in strings of one hundred as a standard, with coins of previous, even ancient issuing all to be found in one string so long as the currency size was right. Cash strings bought by Fredrick Schjoth for his hobby would often have ancient pieces in with recent pieces. It made his hobby interesting when he would send a servant to the market to just purchase strings of coins which he would cut loose and sort through to find all ages of coins.

The hole in round coinage quickly went from round to square. This was for several reasons. The casting method of the money tree left earlier coins with break-off spurs and rough or very sharp edges. Soon came the idea to clean up the coinage for handling by filing the edges. Many coins would be slid onto a holding peg or pin. But the round holed coins would spin on the holding peg. The idea of a square peg in a square hole stopped a batch of coins from spinning while being filed. Coins then were cast with square holes, but sometimes when the square holding peg was forced through the holes in a stack of these coins to be cleaned the alignment would be off a few and a rosette hole or eight-pointed hole would be created in these ones.

 

4.          Corrosion and UN-refining  (What happens to ancient  metal as it ages?)

Patination process for all bronze and copper coins

1^st layer is cuprous oxide, brown in color.

2^nd layer is copper carbonate, green in color.

3^rd layer is green malachite.

Artifacts such as coins are made from metals that have been altered in two ways. Firstly a pure metal is refined from its ore by heat, and secondly it is alloyed, or combined with other refined metals, again with heat, to create new metals with improved useful properties. Bronze is generally 85% copper and 15% tin melted together.

Metal minerals in nature are generally fairly stable in the form they are found in the ground. Malachite, for instance, is a stable form of copper found in nature. It has naturally combined with things in the environment to create a substance that looks almost nothing like the metal copper, yet it is made of more than 70% copper and can be refined to create metallic copper. The metal copper is not stable, and when it is returned to the ground, it will slowly unrefine and recombine naturally with elements in the soil and atmosphere. The most common causes of corrosion, the chemical deterioration of a metal or metal alloy, are contact with water and oxygen, though other substances in the earth and in the atmosphere can also cause corrosion. The result, within a few hundred years will be a layer of malachite and other related minerals on the surface of the artifact as seen more dramatically in this lower corner of a Chou Dynasty spade coin which is over 2000 years old.

The corrosion of copper generally stops after a thin layer of cuprous oxide, brown in color, forms on the exposed surface of the metal. This is the tarnish we see on our pennies after one year. This layer acts as a barrier to further contact with oxygen. When the layer is a green patina, or film, it is copper carbonate and is called verdigris. It is a green crystallized substance produced by the weathering action of acetic acid on copper (shall we say acid rain). In many instances buildings with copper-clad roofs and trim are deliberately allowed to develop patinas because the color is considered attractive.

Malachite is a secondary mineral of copper. This means it is formed when other chemicals alter copper minerals. It occurs when carbonated water interacts with copper minerals, or when a solution of copper interacts with limestone. It is opaque and always green. Malachite crystals sometimes form as needles that fan out from the rock in which they are embedded. Malachite’s presence in oxidized copper deposits helps serve as a prospecting guide for copper to geologists.

A second important thing happens to aging alloyed metals. Being a combination of two or more metals they may separate slowly into their components. For example adding a little bit of copper to silver, and in silver coins that is about 1.5 to 15% copper, makes the normally soft silver harder, and more resistant to wearing down. But silver and copper don't really mix all that well, and over time (300-500 years or more), at normal temperatures; the copper will sometimes begin again to separate itself from the silver. This happens at the microscopic grain boundaries or edges of the copper with the silver. This is known as crystallization of the metal to coin collectors. More correctly it is really just the crystals of the metal becoming visible as the copper comes out of the alloy and begins to corrode; thus weakening the metal alloy and the coin becomes brittle.

 For bronze pretty much all of the changes that occur over time are the result of interactions of the copper in the alloy with the environment. The tin component in bronze is relatively inert and is stable in alloy with copper, it won't separate like silver and copper. Depending on age, soil conditions and a few other things they are collectively referred to as 'the conditions of preservation' and they are interchangeably referred to as patina, patination, encrustation, or verdigris. True patination on older coins (+500 years) is hard and develops as described in the list at the beginning of this section and is usually very irregular and mottled. Manufactured patinas are usually easily rubbed of or brushed off unless glues such as epoxies have been used, a small scrapping with burn under a flame exposing the use of such glues. Familiarity with true patinas is the start of knowing older coins that have undergone natural patination.

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