Coin Metals and Purity

The metal a coin is made from affects its appearance, weight, value, and how it ages. This guide covers the metals used in coins and bullion, how purity is measured, and the difference between solid, clad, and plated construction.

Precious metals

Precious metals are rare, naturally occurring metals valued for their scarcity and resistance to corrosion. They form the basis of bullion investing and have been used in coinage for thousands of years.

Gold (Au)

The most traditional precious metal for coinage. Gold doesn't tarnish, corrode, or react with air or water, which is why ancient gold coins can look almost new after 2,000 years. Pure gold is soft, so most gold coins are alloyed with small amounts of copper or silver for durability.

Common gold coins include the American Gold Eagle (.9167 fine, 22kt), the Canadian Gold Maple Leaf (.9999 fine), the South African Krugerrand (.9167 fine, 22kt), and the Austrian Vienna Philharmonic (.9999 fine).

Silver (Ag)

More abundant and more affordable than gold, silver has been the most widely used precious metal in coinage throughout history. Silver tarnishes over time, developing a surface patina that ranges from light yellow to deep black. Many collectors consider natural toning attractive.

Common silver coins include the American Silver Eagle (.999 fine), the Austrian Vienna Philharmonic (.999 fine), and historically, most circulating coins before the mid-20th century contained silver. The US removed silver from dimes and quarters in 1965.

Platinum (Pt)

Denser and rarer than gold, platinum is used for premium bullion coins. It's extremely resistant to corrosion and doesn't tarnish. Platinum coins are produced in smaller quantities than gold or silver and carry higher premiums over spot price.

Examples include the American Platinum Eagle, the Canadian Platinum Maple Leaf, and the Austrian Platinum Philharmonic.

Palladium (Pd)

The newest precious metal to appear in bullion coinage. Lighter than platinum but with similar properties. The American Palladium Eagle, introduced in 2017, is the most prominent palladium coin. Palladium prices can be volatile compared to gold and silver.

Base metals

Base metals are common, inexpensive metals used in everyday circulating coins. They're chosen for durability, low cost, and distinctive appearance.

Copper (Cu)

One of the oldest metals used in coinage. Copper is soft, easy to strike, and has a distinctive reddish colour that gradually turns brown through oxidation. Used on its own for small denominations (pennies, centimes) and as a major component in many alloys. Pure copper coins develop a brown or green patina over time.

Nickel (Ni)

A hard, silvery-white metal resistant to corrosion. Used in many modern circulating coins, either pure (the US 5-cent "nickel" is actually 75% copper and 25% nickel) or as part of cupronickel alloy. Nickel gives coins a bright, silvery appearance.

Zinc (Zn)

A bluish-white metal used primarily as a core metal with copper plating. Modern US pennies (since 1982) are 97.5% zinc with a thin copper coating. Zinc is cheap but corrodes easily if the plating is breached.

Aluminium (Al)

Extremely light and resistant to corrosion. Used in small-denomination coins in many countries, particularly in Asia and the former Soviet bloc. Aluminium coins feel distinctly lightweight in the hand.

Steel

Iron-based metal sometimes used for wartime coinage when other metals were needed for the military effort. US 1943 pennies were zinc-coated steel. Modern steel coins are typically plated with copper, nickel, or brass to prevent rusting.

Common coin alloys

Most coins are not made from a single pure metal but from alloys — mixtures of two or more metals combined to achieve the right balance of appearance, durability, and cost.

Purity and fineness

Purity describes what proportion of a coin or bar is made of the primary precious metal. It's expressed in two ways: millesimal fineness and karat (for gold only).

Millesimal fineness

Fineness is expressed as parts per thousand of pure metal. A coin that is .999 fine contains 999 parts per thousand of the precious metal — or 99.9% pure. This is the standard system used worldwide for bullion products.

The karat system (gold only)

Karat (abbreviated kt or K) is an older system used exclusively for gold, measuring purity in 24ths. Pure gold is 24 karat. The karat system is common in jewellery but less common in numismatics, where fineness is preferred. Still, you'll encounter it frequently.

The practical difference between 22K and 24K gold coins: 22K coins are harder and more resistant to scratching because the copper alloy adds strength, but 24K coins contain more actual gold per ounce. A 1 oz American Gold Eagle (22K) weighs 33.93 grams total but contains exactly 1 troy ounce (31.1g) of pure gold — the extra weight is copper and silver alloy. A 1 oz Canadian Maple Leaf (24K) weighs 31.1 grams and is essentially all gold.

Coin construction methods

Beyond the choice of metal, how a coin is physically assembled affects its properties, appearance, and collectability.

Solid (single metal)

The coin is made entirely from one metal or alloy throughout. Most historical coins and all bullion coins are solid construction. A silver dollar is solid .900 silver. A gold Sovereign is solid .9167 gold. You can verify by checking that the edge shows the same metal as the surfaces.

Clad

Multiple layers of different metals bonded together mechanically before striking. The US dime and quarter are clad: a pure copper core sandwiched between cupronickel outer layers. You can see the copper core on the edge. Clad construction was introduced in 1965 when rising silver prices made silver coins impractical for circulation.

Plated

A thin coating of one metal electroplated or chemically deposited over a core of a different, usually cheaper metal. Modern Euro coins use various plating techniques — the 1, 2, and 5 cent coins are copper-plated steel. The plating is much thinner than clad layers and can wear through over time, exposing the base metal underneath.

Bimetallic

A coin assembled from two separate metal components — typically a ring of one metal or alloy surrounding a centre disc of another. The 2 Euro coin, the UK £2, and the Canadian $2 (Toonie) are all bimetallic. The two metals are mechanically joined during the minting process. Bimetallic construction adds security against counterfeiting because the two-component assembly is difficult to replicate.

Tri-metallic

Three separate metal components. Rare in circulating coins but occasionally used for commemoratives. Some experimental and collector coins use three distinct metal rings or zones.

Identifying coin metals

A few practical ways to determine what metal a coin is made from, short of destructive testing:

• Weight and size — precious metals are dense. A genuine gold coin feels noticeably heavy for its size. A silver coin is heavier than a similar-sized cupronickel coin. If a coin feels too light for its claimed metal, that's a red flag.
• Magnet test — gold, silver, copper, and aluminium are not magnetic. Nickel is weakly magnetic. Steel and iron are strongly magnetic. If a supposedly silver coin sticks to a magnet, it's steel (possibly plated). This is the simplest counterfeit detection test.
• Edge inspection — a clad coin will show a visible copper line at the edge. A plated coin may show base metal where the plating has worn through. A solid coin shows uniform metal throughout.
• Colour — copper is reddish, cupronickel is silvery-white, brass and nickel-brass are yellow-gold, Nordic gold is a warm golden colour. If the colour doesn't match the expected alloy, investigate further.
• Sound — silver coins produce a distinctive high-pitched ring when tapped or dropped on a hard surface. Copper and clad coins produce a duller sound. This "ring test" takes practice but is surprisingly reliable.