Various metals and alloys are used in minting coins and medallions, offering a wide variety of color, texture, luster and hardness. The raw material cost of metals varies significantly, and certain precious metals are struck as bullion of rated purity and traded for investment purposes. After the content metal is chosen, the end result will still vary depending on how the coin is finished, for example, whether it is antiqued, plated in whole or selectively, or is enameled in one or more colors. Each metal below links to a page providing a more full description of its characteristics along with sample images of the coins from that metal.
Brass, as an alloy of copper and zinc, is used in custom coinage in several forms and is a popular choice. Zinc content within brass alloys can vary and that variance can change the color (as well as hardness) of the resulting alloy. The color can range from somewhat reddish, a yellow gold color, to a silvery color or even a shade of green. MerlinGold®, a proprietary brass alloy with a mirror finish developed by Northwest Territorial Mint, has a gold-like surface resulting in a very detailed and proof like coin. Such a coin can have satin lustered surfaces to contrast to a highly reflective background. Brass alloys also respond well to antiquing, a process of applying an antique-like finish to the coin surface and selectively buffing the highlighted areas. Such a finish is often termed bronze, though this is not actually a bronze alloy. Enameling a portion of the coin is another finishing option that can add distinction. Almost any color or combination of colors can be done, with red, white and blue being especially popular. Some enamels can provide a gradation in tone along the enamel edges. The enamel process itself is done after the coin is minted, and is applied by hand by an artist with precision instruments under high magnification. Brass alloys are generally harder metals than silver or gold and will have better wear properties. In order to selectively plate brass alloys with gold, the coin must first be plated with nickel in order to avoid metal migration, and then it can be completely or selectively gold plated. The brass metal, as a raw material used by the mint, comes in a variety of forms. Often used from rolled metal, ready for straightening and blanking. It is also available in strips and plates. 230 brass and 260 brass are two common alloys available in which the alloyed zinc differs.
Copper is a soft reddish metal known since ancient times. Metallurgy began with the simple beating of malleable copper into the shape desired. It has a wide variety of applications in industry, most often found in electrical wiring, plumbing and automotive uses. It is a metal found frequently alloyed with others – with tin for bronze, or zinc for brass. Although used as a coating on the U.S. penny, copper’s softness leaves it with wear properties that are less than ideal for use in general circulation coins. For some kinds of custom minted coins, however, copper can be a fine choice, and indeed is a popular choice in regions where copper mining is done. Such coins, when minted in a proof like finish, will exhibit copper’s distinctive red color, with good detail. Copper responds well to antiquing and can also be greened, offering good flexibility with coin finishes. Copper has been recently selected as the metal to be used in the minting of a coin honoring the USS Abraham Lincoln minted for the U.S. Navy. Copper is also a frequent choice as the underlying metal in the minting of large plated coins. The appearance of such a coin takes on the characteristics of the plating, not the copper, but the use of copper can be a less expensive option than a coin made entirely of the plated metal.
Another popular alloy used in the minting of custom coins is a nickel colored alloy of copper and nickel. Called cuper nickel as used by Northwest Territorial Mint for coins, it is a hard wearing alloy of 75% copper, 15% nickel and 5% zinc as the three primary metals. It can be struck into a proof-like coin with a mirror finish. Cuper nickel can also have an antique finish applied for an elegant aged look. This process can add more contrast to intricate coin designs, with raised portions of the coin having a lighter tone and somewhat higher luster. Cuper nickel can provide a striking surface for an enameled finish, with some reds and blues contrasting well with the nickel color of the base metal. Cuper nickel can also be selectively plated with gold for a large variety of appearances, allowing the gold color to contrast nicely with the chrome of the base metal. Cuper nickel is much harder than most other popular coinage metals. Because of its wear characteristics it has also been used in general circulation coins and is in the present day British 20p coin and some coins of Russia. Cuper nickel is somewhat more expensive than brass.
Silver and gold are the oldest of coinage metals, with the earliest coins minted in electrum, a naturally occuring alloy of gold and silver. Its beauty and malleability have contributed to coin use. Silver is a somewhat rare and expensive coinage metal, although neither as rare nor expensive as gold. Unlike gold, it has a brilliant white luster. Silver is very ductile and malleable, only slightly less so than gold, and a little harder and less dense. Silver is resistant to tarnishing in pure air and water, but exposure to ozone, sulphur, hydrogen sulphide and other compounds will cause tarnishing. In chemist terms, the tarnish is an accumulation of silver sulphide. Silver has a wide variety of industrial applications. Among other things, silver compounds form the basis of conventional photography and x-ray technologies. As a coinage metal, silver can exhibit a wondrous satiny luster and hold the tiniest of coin details. Proof coins made from silver are a true delight to the eye, though such coins can be difficult to photograph. Silver coins can be finished in a number of ways. Because it is such a beautiful coinage metal, a proof coin of silver is often held up as among the finest example of the minter’s art, with backgrounds holding a highly mirrored finish and raised sections often appearing as a lustrous white satin.
Another beautiful option is to “gold select”. In this technique, a selected portion of the coin receives gold plating, resulting in a two tone effect, with gold contrasting with the silver. An antique finish can also be applied, resulting in a distinctive aged appearance to the coin. Enameling can also be done. As a precious metal, silver is traded in bullion form, and bullion coins are a trading commodity subject to the market price of silver. As a raw material, it comes to the mint in a variety of forms: as bars and rounds of silver bullion, as silver ingots, or as billets. Bullion or ingots must be melted down and formed into billets, a cylindrical form of silver of slightly over 400 Troy ounces. Care is required when melting silver because of a tendency of the metal to absorb oxygen when molten, a significant problem if the material is destined to be unblemished coins. Silver can also arrive at the mint as billets already formed. The billets are then extruded into a strip that is ready for blanking.
Gold and silver are the oldest of coinage metals, with the earliest coins minted in electrum, a naturally occuring alloy of gold and silver. Gold has long been a highly valued and rare metal, civilization’s ultimate measure of wealth and universally accepted medium of exchange. Historically, gold was used for storing value when ordinary currency was losing value. When paper currencies fail, investors purchase gold and silver to preserve accumulated wealth. This precious metal is sufficiently rare that a single 20 yard cube could hold all of the gold ever mined. Gold is among the most ductile of all the coinage metals, and able to be made into sheets of extremely thin metal of as little as .00001 inch. This last characteristic, along with gold’s inherent beauty and lustrous detail, make it a highly sought choice for selective plating on coins of another metal. Gold is also sometimes minted directly into valuable coins. Valuable collector’s items, such coins are timeless in their retention of detail and finish. Gold coins are most often finished as a proof coin. Such a coin would be held up as among the finest example example of the minter’s art, with backgrounds holding a highly mirrored finish and raised sections often appearing as a lustrous gold satin. Because of gold’s beauty, it is a popular choice to use in selectively plating a coin of another metal, like silver. This option is termed to “gold select”. In this technique, an electrolytic process allows a selected portion of the coin to receive gold plating, resulting in a two tone effect, with gold contrasting with the silver. As a precious metal, gold is traded in bullion form, and bullion coins are a trading commodity subject to the market price of gold. Gold most commonly arrives at the mint in the form of bars or ingots. The bars can be rolled directly into a metal that can be blanked. It can also be melted, formed into billets and then rolled. The metal price will drive the price of coins that are pure gold and makes them quite valuable in addition to beautiful.
Palladium and platinum are precious metals of the platinum group with a wide number of industrial applications in addition to bullion and coin usages. Palladium is a steel-white metal, does not tarnish in air, and is the least dense and lowest melting of the platinum group of metals. However, its melting point is still above that of the more commonly used coinage metals. Palladium is highly lustrous, and can exhibit a bit of bluishness, especially noticeable in its industrial application in halogen lights. When palladium is annealed, it is soft and ductile, and cold working greatly increases its strength and hardness. Like gold and silver, this rare precious metal is minted into bullion for investment purposes, and can also be used as the basis for custom coins. This metal comes from refiner Johnson Matthey in strip form ready for blanking by Northwest Territorial Mint. For more information about palladium metal, please visit this palladium web site. Platinum, the most common metal of the platinum group, has similar characteristics as palladium, and is also traded in bullion form. Its demand in industrial applications has soared in the last couple decades for use in catalytic converters and other emissions control purposes. Since the early 1990s, platinum remains the preferred metal among various celebrities. It is regarded as the symbol of beauty and timelessness, the ultimate in elegance. Coins minted from this metal have a white-silver appearance. Other metals can be used for coinage as well, but their use is more rare. Northwest Territorial Mint has minted coins in niobium and in zirconium in which the customer, the Wah Chang Company, supplied the difficult to obtain source metal.