How and why bi-metallic coins are made is, for most people, a complete mystery. However, from a general numismatic point of view, it’s important to understand how bi-metallic coins are made.
Bi-metallic coins are made by first creating a metal core, and then forming the second metal around that. This can be achieved using a variety of methods, such as drilling or punching, and heat and pressure are both involved to make the process easier.
Often used to fill gaps in currency security and political need, as well as to aid human deviousness, bi-metallic coins are a window into history. The methods of making them have differed, but the basics are the same. Below, we take a closer look at these methods.
How Bi-Metallic Coins Are Made
While there have been many different methods of creating bi-metallic coins, the basics are the same. That process is as follows:
- A metal core is created
- That metal core is allowed to cool and is modified to hold the secondary metal
- The secondary metal is affixed to the base metal core
The last step is accomplished by one of several different methods:
In this method, a core of one metal is coated with another metal. The earliest recordings of this type of coinage are from Ancient Rome. It is often done to hide a debased currency.
For example, with solid silver coins that have been devalued, a copper core might be coated with a silver topping. The value of the coin would reflect the silver topping even though its core was copper.
Debased currency is not always the motivation behind this. In the USA, silver coins were given a metallic clad center and a silver coating to alleviate a perceived shortage of silver in the early 1960s. Another example is the American penny.
American pennies used to be solid copper or copper with a very small amount of zinc to add hardness to the coin. In 1982 and 1983, solid copper coins were phased out. In their place was a zinc core coated with a copper base. The US did this to combat the rising costs of copper.
This method was used by Charles I with the English Rose Farthing. In this method, a secondary piece of metal is “punched” or stamped into the primary coinage metal. With the English farthing, a brass wedge was inserted into a copper core to combat counterfeiting.
In this method, an external ring is manufactured via a multiple die tool that punches a center hole in a blank. The inner metal has special milling on its perimeter, which allows it to penetrate the outer ring metal when struck. The exact method is proprietary to each manufacturer.
This method works because the pressure needed to extract the inner ring would destroy the outer ring. Once the coin is struck it is almost impossible to extract the center.
Another method that has been used is to drill a hole into a base blank and then insert a secondary metal into that hole. The coin is then struck, making the secondary piece mold to the base blank.
Commonalities Between Production Methods
Heat is used to soften the metals to make them malleable, which make it easier to insert the secondary metal. This works whether the characteristic that holds the secondary metal in place is ridged milling or being inserted into a hole or indentation on the base metal disc.
Striking is the term for applying the pressure needed to join the two coins together. The pressure needed for each type of coin is different. All bi-metallic coins have some sort of striking process that uses pressure to meld the two metals together.
Virtually all bi-metallic coins have some sort of edge that helps hold the two metals together. With coins that have a metal center different to that of the outer ring, ridges are put on the edge of the inside piece of the coin. When the coin is struck, the outer edge molds to the ridges, firmly holding the secondary metal in place.
Primary And Secondary Metal
The primary metal tends to be malleable, at least after it has been heated. The secondary metal tends to be stronger and less susceptible to changing form. This helps prevent counterfeiting. It also allows governments to control how much of the secondary metal will be introduced into the currency.
The History Of Bi-Metallic Coins
To fully understand the process of making bi-metallic coins, you must understand the history and the evolution of these coins. The first step in gaining that perspective is to realize three points:
- Bi-metallic coins have been used as currency, as substitutes for currency, as tokens of appreciation, and as collectibles
- Bi-metallic coins have always augmented some need of local, regional and national governments and the political leaders that run them
- Rarely, bi-metallic coins have been used by private individuals as a symbol of commemoration
History Of Bi-Metallic Coins
The use of bi-metallic coins dates back millennia. While early versions of coins with more than one metal were accidental or opportunistic, both ancient Rome and Greece used them as both currency and as awards for various public deeds.
Single Metal Coins
As the term implies, initially, coins were only made of a single, solid metal. They were usually made with a precious metal, like gold or silver, but occasionally were made of more common metals like copper, lead and tin.
The earliest coins date back to the 7th century BCE. These coins were made of a naturally occurring alloy of gold and silver called electrum. It is these coins that serve as the first recorded occasion that bi-metallic coins were used in an official capacity.
4th Century CE
The first recorded, intentional creation and use of bi-metallic coins dates to the 4th century, CE. The Roman Empire issued coins for special occasions, like showing heroism in battle. These coins were usually gold and quite large. Recipients, particularly barbarians, would drill a hole in them and wear them around their neck.
Eventually, the gold coin was ensconced in a more common metal, both for safe keeping and aesthetics. This was technically one of the first human attempts at creating a bi-metallic coin. The Romans also created bi-metallic coins, using the second metal to fight counterfeit coins. Before them, the ancient Greeks reportedly did the same.
A little later, in 1625, Charles I of England commissioned the English Rose Farthing. This featured a brass wedge inserted into a copper disc. The copper wedge served as an anti-forgery device. In Cologne, Germany, in 1730, a copper plug served as the core of a silver token.
18th, 19th And 20th Centuries
The US Mint created a bi-metallic cent coin to regulate coin size in accordance with the Coinage Act of April 2, 1792. A copper blank was created with a punched small hole in which a silver plug was infused. Once the silver was inserted, the coin was struck by a die. Britain, France and Germany also had semblances of bi-metallic coins, although few were used for currency at this time.
Throughout the 19th and 20th centuries, bi-metallic coins have been introduced by over 100 countries. The initial, widely used bi-metallic coin was the 500 Lira coin in Italy in 1982. Coins minted today use many different combinations of precious metals, including:
- Copper with nickel
- Brass with nickel
- Yellow and white gold
- Gold and silver
- Silver and titanium
- Silver and nickel
- Non-magnetic stainless steel and aluminum bronze
The USA has used bi-metallic coins periodically in three main forms:
- As raw currency
- As token currency
- As a commemorative piece
The USA has had bi-metallic coins in circulation dating back to the Coinage Act of 1792. At various intervals, primarily to offset value or to thwart the production of fake coins, bi-metallic coins have been implemented, usually only for a brief period.
Currently, the only bi-metallic coin in circulation that has a specific purpose of presenting two metals in the open is the $10 Library of Congress commemorative coin. This coin features a platinum center surrounded by a gold ring. These coins are used almost exclusively to secure against counterfeiting.
Bi-metallic coins have been used by municipalities and state governments in the USA for quite some time as a substitute for currency. Some examples include:
- Public transportation tokens on trains, buses and subways
- Toll tokens for bridges and roadways
- Public attraction tokens for places like museums and gardens
Someone using these tokens purchase them using actual currency. Their purpose is to streamline gaining entry or usage of the attraction, road or mode of public transportation in question. Usually, tokens like this are not worth any currency directly, unless sold to a third party (which may or may not be legal).
Both the US government and various states have commissioned bi-metallic coins to commemorate occasions, people, and places.
Two Principal Types Of Bi-Metallic Coins
Bi Metallic coins generally come in two different formats.
Interior Metal Core
This type of bi-metallic coin has a shell of one type of metal and a core of another. In most cases, bi-metallic coins of this type are made for economic reasons. For example, the American government discontinued 100% silver coins during a silver shortage, moving to a bi-metallic version that still exists today.
In another example, the US government migrated copper pennies to copper and zinc in the early 1980s because the price of copper was increasing dramatically, increasing the production costs of the penny to more than one cent.
Visible Bi-Metallic Core
These types of coins have an outer edge of one type of metal and an inner plug of another metal. There are many different reasons these types of coins are produced. Some countries created them to have a distinctive coin. Other countries minted coins with a visible bi-metallic core to commemorate something. Others have used this type of coin to thwart counterfeiting.
Secondary Metal Formats
Almost all bi-metallic coins have an outer shell or ring of one type of metal. The other metal usually comes in one of several formats:
Wedges were first employed by King Charles I of England. The Rose Farthing Token was produced from 1636 through 1644. The minting of this type of coin was terminated due to the English civil war.
Various types of wedges have been employed sporadically since then. They have been struck in Australia, England, the USA, Germany, and many other countries. Variations of the initial wedge are generally used now.
The first plug was used by Charles II of England as part of a major currency reformation, or at least that is what he told himself. The price of tin had cratered in the early 1680s and Charles II had significant holdings in tin mines and land interests in Cornwall. To prop up the price, the currency change was commissioned.
To do that, all halfpennies and farthings were struck in tin. They featured a copper plug inserted into the middle of the blanks before they were struck. The coins of copper and tin were struck from 1684 through 1692.
The US produced a cent piece with a silver plug in 1792. 75% of the cent’s worth was the silver plug. It was necessary to stabilize the weight in value of currency as the US Mint struggled to produce coins of equal value within the tolerance thresholds for specific metal content in coins.
When a coin was too heavy, the US government lost money. When a coin was too light, merchants lost value in their currency. The plug equaled the value against the disparity of weight in a copper coin. Interestingly, many coins of that era have adjustment marks as the mint perfected plug size.
Bimetallic patterns have also often been used, primarily to thwart counterfeiting. During the reign of Charles II, private and public coins with bi-metallic patterns were incorporated into base metal coinage. The metals used were usually copper with an inner brass ring (or this combination in reverse), or tin with a brass or copper ring in the middle.
Cladding is the process of inserting a secondary metal into a coin disk of another metal. This approach produces at least three layers of metal in a coin:
- Two outer layers
- At least one inner layer of a secondary metal
The best example of this type of bi-metallic coin are US quarters and pennies. Both have interior base metals that are surrounded by an outer metal (usually nickel and copper respectively). There are several reasons cladding is used.
The cost of the external metal exceeds the value of the coin, thus tempting individuals to melt the coins for their metallic value. An example of this is when copper in the late 2000s skyrocketed because of the recession and pennies were worth more in terms of their copper content than in their fiscal value.
Another example happened with gold in the 1930s. In this case, gold was confiscated from individuals and gold coins stopped being minted. While no clad gold coin was designed, several were mentioned as an alternative to outright confiscation of gold from the citizenry.
This is along the same lines as the reason above, but is directly linked to the cost of producing the coin. If a silver coin, for example, is worth 1 cent but the metal value is a full cent and the production value is a half cent, the government would lose money producing every coin. To combat this, a metal of a lesser value is used at the core of the coin.
As happened in the USA in the 1960s when silver was in short supply, the US began using a cladding process for previously pure silver coins.
With this type of bi-metallic coin, a ring of one metal surrounds a core of another metal. There are several examples of this type of bi-metallic coin:
- Australian 5 dollar coin (1996, Bradman, aluminum-bronze center with a stainless-steel ring)
- New Zealand 50 cent coin (1994, aluminum-bronze center with a nickel ring)
- Austria 500 schilling (1995, Austrian membership to the European Union (EU,) silver center in a gold ring)
- Italy 500 lira coin (1982-1995, bronze center in a stainless-steel ring)
Center With Outer Ring
This type of bi-metallic coin has a large central clad core made up of three different metals. This clad core is surrounded by a ring of another metal. Technically, this is not bi-metallic, but the appearance makes them look like one. They are also accepted by most collectors and dealers as bi-metallic.
Examples of these include:
- EU 2 Euro (2002, nickel-brass clad nickel center in a cupro-nickel ring
- EU 1 Euro (2002, cupro-nickel clad nickel in a nickel-brass ring
- 10 Franc (1988-2000, steel center and aluminum bronze ring)
- 100 Escudos (1988, Portugal, copper, nickel aluminum, bronze)
- 5 and 10 Rubles (Russia, 1991)
- 10, 20, 30 dinars (Algeria)
- Various bi-metallic coins by Botswana, Brazil, Canada, Hungary, Lithuania, Morocco, Poland and Turkey
Bi-metallic coins are made using a variety of methods, such as drilling, punching and coating. Heat and pressure are used to make the metals involved more malleable, and bi-metallic coins can be made from a variety of both precious and non-precious metals.