Coining (mint)
Encyclopedia
In minting
, coining is the process of manufacturing coin
s using a kind of stamping
which is now generically known in metalworking
as "coining".
A coin die is one of the two metallic pieces
that are used to strike one side of a coin
. A die contains an inverse version of the image to be struck on the coin.
Modern dies made out of hardened steel
are capable of producing many hundreds of thousands of coins before they are retired and defaced.
in the 3rd century, dies were still used even when they became very worn or even when they cracked. The die that was on the hammer side, usually the reverse (back), tended to wear out first. The flan
s were usually hot prior to striking. On some Roman provincial coins
, some believe the tongs used to move the heated flan left permanent center indentations on the finished coins. Others attribute these marks to surfacing tools used as a part of flan preparation.
The vast majority of medieval coins were cold struck; the planchet
s were not heated. While medieval coin dies were largely made of iron, some dies have been discovered with a small region at the face of the die which is made of steel. As technology and the economy changed over the course of the Middle Ages, so did the techniques used to create coin dies. While most ancient coin dies used engraving very heavily, early medieval coinage was dominated by dies created mostly from punches, which displace the metal of the die instead of removing it. There is evidence of medieval die cutters using engraving tools to lay out designs, and to create detailed punches. However, engraving on the face of the die did not become commonplace until the early Renaissance.
Very detailed records exist for the Venetian mint. In the late Middle Ages, the dies used to create tornesellos lasted as follows: "hammer" die, ~17,000 strikes; "anvil" die, 36,000 strikes. The mint made an average of 20,000 coins per day, so they were making one hammer die a day and one anvil die every other day. The "hammer" dies wore out quicker because they tended to be smaller and were hit directly with a hammer, leading to severe mushrooming on the tops.
model of the coin. The plaster model is then coated with rubber
. The rubber mold is then used to make an epoxy
galvano. All of this takes place on a scale of around eight inches. Next, a Janvier reducing lathe takes several days to reduce the image onto a steel master hub. The master hub is then heat treated to make it hard. The master hub is then used to make only a few master dies via hubbing
, which involves pressing the master hub into a steel blank to impress the image into the die. The master die is then used to form as many working hubs as needed through the same process, and then the working hubs are put through the same process to form the working dies. These working dies are the actual dies which will strike coins. The process of transferring the hub to the die can be repeated as many times as necessary in order to form the number of dies needed to make the amount of coins required. The difference between a hub and a die is that the hub has a raised image and a die has an incuse image, so one forms the other.
When making working dies, the Mint has found that by using a lower amount of pressure in the hubbing press, they can prolong the life of the hubs and dies used. In between each hubbing, however, the die being made must be subjected to an annealing
furnace to soften the steel, making it easier to push the image into the die. As the die is compressed in the hubbing press, the molecular structure of the steel changes. The large amount of pressure exerted on the steel forces the molecules of the steel to be compacted, making this hubbed die much stronger and denser. If, when the die is subjected to another hubbing, it is not lined up exactly with the hub, the result is a secondary image, or doubling. This is called hub doubling, and results in such spectacular coins as the famous 1955 doubled die cent
.
, called reeds. Some older US coins, and many world coins have other designs on the edge of the coin. Sometimes these are simple designs like vines, more complex bar patterns or perhaps a phrase. These kinds of designs are imparted into the coin through a third die called a collar. The collar is the final size of the coin, and the planchet expands to fill the collar when struck. When the collar is missing, it results in a type of error called a broadstrike. A broadstruck coin is generally a bit flatter and quite a bit bigger around than the regular non-error coin of the same denomination.
If there is more than one die used for either the front or the back, then minute differences between each die can be identified. In addition, the relative positioning between the back and the front can also be used to determine which dies were used for the run that produced a particular coin. In the United States, coins are typically minted head to tail; that means the "top" of one side of the coin is on the exact opposite side of the coin as the "bottom" of the other, resulting in the coin's features being presented right side up when the coin is turned on a horizontal axis. This is called a "coin turn" alignment. Correct alignment for a "coin turn" is exactly 180 degrees; however due to realities of machine process, this can vary by a fraction of a degree. In rare cases, this deviation can be up to several degrees, and very easily noticeable. However, even very small deviations can establish the production run in which a coin was minted. When this is done, it is called a die marriage. Die marriage is particularly important with regards to the US half dollar minted at the New Orleans Mint
in 1861, since it establishes if a coin was minted with the mint facility under Union, State of Louisiana, and Confederacy control.
, one of the main metals used in today’s coins, is exceedingly hard and causes wear quickly. Copper
has been used for centuries because of its malleability and the ease with which it makes coins. However, it too wears the dies when they are used for too long. An infamous example is the 1955 "poorman’s double die." This coin is sold as a replacement for the 1955 doubled die, but it is no more than Die Deterioration Doubling, caused by wear on the dies. When a coin is struck, the planchet is not heated. Although the planchet would be softer and more malleable, the extra time and expense would prove too great for the mint. Thus, the metal cold flows into the die under the high pressure.
Mistakes can happen at any stage of this manufacturing process, and these mistakes are something that certain collectors look for. Coin errors that occur on the die are generally more desirable than errors made at the time of the strike. For example, a doubled die, where a date or another device appears twice slightly offset, is often a highly desired error. Strike errors are generally unique, whereas all coins struck with an error die will have the same characteristic. This makes them more easily collectible. The most famous doubled die in the past hundred years is the 1955 doubled die
Lincoln cent. These trade for hundreds of dollars because the error can easily be seen by a casual observer. Many doubled die errors require at least a jeweler's loupe
to be seen. Doubling can occur at the hub stage as well. Some more recent errors are hub doubled. Most famously, there is a 1995 doubled die cent that is hub doubled.
More typically, a terminal die state will result in crack-like structures appearing on the coin. A good example can be observed on an 1839 Liberty Seated Dime. A crack-like feature is clearly seen going through the date, the shield, and the second star. (Source: www.seateddimevarieties.com, Major 100 Varieties, number 12 has the most pronounced features) This crack-like structure appears like material that is overlaid onto the surface of the coin; this is because the crack on the die allowed the planchet materiel to flow into it during stamping, just like a deliberate design feature. Some coins exhibit multiple crack-like features, indicating a die that is very close to the end of its serviceable life. Coins that do exhibit such features can be labeled as “Terminal Die State” examples.
A coin die itself, has been the main motive for many collectors coins and medals. One of the most recent and famous one, is the Austrian 700 Years City of Hall in Tyrol coin, minted on January 29, 2003. The reverse side of the coin shows the Guldiner silver coin. However, the design is negative, representing a coin die, as a reference to Hall’s history as a significant centre for minting coins.
Mint (coin)
A mint is an industrial facility which manufactures coins for currency.The history of mints correlates closely with the history of coins. One difference is that the history of the mint is usually closely tied to the political situation of an era...
, coining is the process of manufacturing coin
Coin
A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....
s using a kind of stamping
Stamping (metalworking)
Stamping includes a variety of sheet-metal forming manufacturing processes, such as punching using a machine press or stamping press, blanking, embossing, bending, flanging, and coining. This could be a single stage operation where every stroke of the press produce the desired form on the sheet...
which is now generically known in metalworking
Metalworking
Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewelry. It therefore includes a correspondingly wide range of skills,...
as "coining".
A coin die is one of the two metallic pieces
Die (manufacturing)
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create...
that are used to strike one side of a coin
Coin
A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....
. A die contains an inverse version of the image to be struck on the coin.
Modern dies made out of hardened steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
are capable of producing many hundreds of thousands of coins before they are retired and defaced.
Ancient coin dies
Prior to the modern era, coin dies were manufactured individually by hand by artisans known as engravers. In demanding times, such as the crisis of the Roman EmpireCrisis of the Third Century
The Crisis of the Third Century was a period in which the Roman Empire nearly collapsed under the combined pressures of invasion, civil war, plague, and economic depression...
in the 3rd century, dies were still used even when they became very worn or even when they cracked. The die that was on the hammer side, usually the reverse (back), tended to wear out first. The flan
Planchet
A planchet is a round metal disk that is ready to be struck as a coin. An older word for planchet is flan. They are also referred to as blanks.-History:The preparation of the flan or planchet has varied over the years...
s were usually hot prior to striking. On some Roman provincial coins
Roman provincial coins
Roman Provincial coins are coins that were minted in the Roman Empire by civic authorities rather than by Imperial authorities. Often these coins were a continuation of the original currency system that existed prior to the arrival or conquest by the Romans....
, some believe the tongs used to move the heated flan left permanent center indentations on the finished coins. Others attribute these marks to surfacing tools used as a part of flan preparation.
Medieval coin dies
Medieval engravers were guild members who created coins in mints.The vast majority of medieval coins were cold struck; the planchet
Planchet
A planchet is a round metal disk that is ready to be struck as a coin. An older word for planchet is flan. They are also referred to as blanks.-History:The preparation of the flan or planchet has varied over the years...
s were not heated. While medieval coin dies were largely made of iron, some dies have been discovered with a small region at the face of the die which is made of steel. As technology and the economy changed over the course of the Middle Ages, so did the techniques used to create coin dies. While most ancient coin dies used engraving very heavily, early medieval coinage was dominated by dies created mostly from punches, which displace the metal of the die instead of removing it. There is evidence of medieval die cutters using engraving tools to lay out designs, and to create detailed punches. However, engraving on the face of the die did not become commonplace until the early Renaissance.
Very detailed records exist for the Venetian mint. In the late Middle Ages, the dies used to create tornesellos lasted as follows: "hammer" die, ~17,000 strikes; "anvil" die, 36,000 strikes. The mint made an average of 20,000 coins per day, so they were making one hammer die a day and one anvil die every other day. The "hammer" dies wore out quicker because they tended to be smaller and were hit directly with a hammer, leading to severe mushrooming on the tops.
Modern die production
First, an artist creates a large plasterPlaster
Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...
model of the coin. The plaster model is then coated with rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
. The rubber mold is then used to make an epoxy
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....
galvano. All of this takes place on a scale of around eight inches. Next, a Janvier reducing lathe takes several days to reduce the image onto a steel master hub. The master hub is then heat treated to make it hard. The master hub is then used to make only a few master dies via hubbing
Hubbing
Hubbing is a metalworking process that is used to make dies. It is a cold-working process, which means that it occurs well below the melting temperature of the metal being worked.-Process:...
, which involves pressing the master hub into a steel blank to impress the image into the die. The master die is then used to form as many working hubs as needed through the same process, and then the working hubs are put through the same process to form the working dies. These working dies are the actual dies which will strike coins. The process of transferring the hub to the die can be repeated as many times as necessary in order to form the number of dies needed to make the amount of coins required. The difference between a hub and a die is that the hub has a raised image and a die has an incuse image, so one forms the other.
When making working dies, the Mint has found that by using a lower amount of pressure in the hubbing press, they can prolong the life of the hubs and dies used. In between each hubbing, however, the die being made must be subjected to an annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
furnace to soften the steel, making it easier to push the image into the die. As the die is compressed in the hubbing press, the molecular structure of the steel changes. The large amount of pressure exerted on the steel forces the molecules of the steel to be compacted, making this hubbed die much stronger and denser. If, when the die is subjected to another hubbing, it is not lined up exactly with the hub, the result is a secondary image, or doubling. This is called hub doubling, and results in such spectacular coins as the famous 1955 doubled die cent
1955 doubled die cent
The 1955 doubled die cent is a die variety that occurred during production of the one cent coin at the United States Mint in 1955. This variety is often mistakenly referred to as an error...
.
The third side of the coin
On the edge of the US dime, quarter and half dollar, and many world coins there are ridges, similar to knurlingKnurling
Knurling is a manufacturing process, typically conducted on a lathe, whereby a visually attractive diamond-shaped pattern is cut or rolled into metal.- Uses :...
, called reeds. Some older US coins, and many world coins have other designs on the edge of the coin. Sometimes these are simple designs like vines, more complex bar patterns or perhaps a phrase. These kinds of designs are imparted into the coin through a third die called a collar. The collar is the final size of the coin, and the planchet expands to fill the collar when struck. When the collar is missing, it results in a type of error called a broadstrike. A broadstruck coin is generally a bit flatter and quite a bit bigger around than the regular non-error coin of the same denomination.
Die Marriage
During a typical production run, or coining process, (particularly when heavy presses are used for large production runs) a die is selected for the front and another die is selected for the back of the coin to be made. In some cases, there is more than one die (front and/or back) from which to select. The mint employee then places each die into the minting press for operation. When the run is complete, the dies are removed from the press. This procedure is repeated for each production run. Coins minted by each mint for each year may have several production runs in order to complete their orders.If there is more than one die used for either the front or the back, then minute differences between each die can be identified. In addition, the relative positioning between the back and the front can also be used to determine which dies were used for the run that produced a particular coin. In the United States, coins are typically minted head to tail; that means the "top" of one side of the coin is on the exact opposite side of the coin as the "bottom" of the other, resulting in the coin's features being presented right side up when the coin is turned on a horizontal axis. This is called a "coin turn" alignment. Correct alignment for a "coin turn" is exactly 180 degrees; however due to realities of machine process, this can vary by a fraction of a degree. In rare cases, this deviation can be up to several degrees, and very easily noticeable. However, even very small deviations can establish the production run in which a coin was minted. When this is done, it is called a die marriage. Die marriage is particularly important with regards to the US half dollar minted at the New Orleans Mint
New Orleans Mint
The New Orleans Mint operated in New Orleans, Louisiana, as a branch mint of the United States Mint from 1838 to 1861 and from 1879 to 1909. During its years of operation, it produced over 427 million gold and silver coins of nearly every American denomination, with a total face value of over...
in 1861, since it establishes if a coin was minted with the mint facility under Union, State of Louisiana, and Confederacy control.
Use
In modern presses, a die strikes approximately 120 coins a minute. This rapid coining causes wear on the dies. NickelNickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, one of the main metals used in today’s coins, is exceedingly hard and causes wear quickly. Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
has been used for centuries because of its malleability and the ease with which it makes coins. However, it too wears the dies when they are used for too long. An infamous example is the 1955 "poorman’s double die." This coin is sold as a replacement for the 1955 doubled die, but it is no more than Die Deterioration Doubling, caused by wear on the dies. When a coin is struck, the planchet is not heated. Although the planchet would be softer and more malleable, the extra time and expense would prove too great for the mint. Thus, the metal cold flows into the die under the high pressure.
Mistakes can happen at any stage of this manufacturing process, and these mistakes are something that certain collectors look for. Coin errors that occur on the die are generally more desirable than errors made at the time of the strike. For example, a doubled die, where a date or another device appears twice slightly offset, is often a highly desired error. Strike errors are generally unique, whereas all coins struck with an error die will have the same characteristic. This makes them more easily collectible. The most famous doubled die in the past hundred years is the 1955 doubled die
1955 doubled die cent
The 1955 doubled die cent is a die variety that occurred during production of the one cent coin at the United States Mint in 1955. This variety is often mistakenly referred to as an error...
Lincoln cent. These trade for hundreds of dollars because the error can easily be seen by a casual observer. Many doubled die errors require at least a jeweler's loupe
Loupe
A loupe is a simple, small magnification device used to see small details more closely. Unlike a magnifying glass, a loupe does not have an attached handle, and its focusing lens are contained in an opaque cylinder or cone. Loupes are also called hand lenses .- Optics :Three basic types of loupes...
to be seen. Doubling can occur at the hub stage as well. Some more recent errors are hub doubled. Most famously, there is a 1995 doubled die cent that is hub doubled.
Terminal Die State
The terminal die state, as the name would seem to indicate, is the last state in which any die is used. This state refers to a die that is starting to develop serious structural failures through cracks. A die in such a state would, if not removed from service, become unserviceable by breaking apart. Like any metallic part, dies are subject to failure from the enormous pressures used to impress the image of the die onto the blank planchet. Some dies were removed when even a microscopic defect is observed, while others were used until they literally broke into pieces. The Bass Foundation has a particularly noteworthy example of an 1806/4 Quarter Eagle ($2.50 gold US coin) in which a piece of the die has broken away, resulting in a heavy rim break over the "LI" in "LIBERTY" on the front. (Source: www.harrybassfoundation.org, HBCC-3014)More typically, a terminal die state will result in crack-like structures appearing on the coin. A good example can be observed on an 1839 Liberty Seated Dime. A crack-like feature is clearly seen going through the date, the shield, and the second star. (Source: www.seateddimevarieties.com, Major 100 Varieties, number 12 has the most pronounced features) This crack-like structure appears like material that is overlaid onto the surface of the coin; this is because the crack on the die allowed the planchet materiel to flow into it during stamping, just like a deliberate design feature. Some coins exhibit multiple crack-like features, indicating a die that is very close to the end of its serviceable life. Coins that do exhibit such features can be labeled as “Terminal Die State” examples.
Coin die represented in other coins
External links
- Designing and minting coins The creation of a die and the minting process
- US Treasury: Preparation of Working Dies