Striking Standards

How coins are made, and why the same design can look dramatically different depending on the striking standard. Understanding the difference between Bullion, BU, Proof, and Piedfort is essential for knowing what you're buying and what you own.

The minting process

Every coin starts as raw metal and goes through the same fundamental steps, though the level of care at each stage varies dramatically between a circulating coin and a collector proof.

Striking standards

The same design struck by the same mint can be produced to different quality levels. These standards determine the finish, detail, and price of the final coin.

Bullion standard

The standard production method. Blanks are struck once at high speed in automated presses capable of producing hundreds of coins per minute. The focus is throughput and consistency rather than cosmetic perfection.

Bullion-standard coins include regular circulating coins (the coins in your pocket) and investment bullion like the American Silver Eagle or Vienna Philharmonic. These coins will have good detail but may show minor bag marks, die polish lines, or slight weakness on the highest points of the design. They're valued primarily for their metal content rather than their finish.

Brilliant Uncirculated (BU)

A step above standard bullion quality. BU coins are struck with more care — often on specially selected blanks, sometimes with freshly prepared dies, and at slower press speeds than circulation coins. The result is sharper detail, better lustre, and fewer surface marks.

BU is not proof quality: the dies and blanks are not polished, and coins receive a single strike. But a BU coin is noticeably cleaner and sharper than a coin pulled from a mint bag. Many mints sell annual BU sets as affordable collector products — a complete set of the year's circulating denominations in better-than-average condition.

Proof

The highest striking standard and the one most associated with collector coins. Proof production involves multiple extra steps that dramatically increase the time and cost per coin.

• Polished blanks — each blank is individually polished to a mirror finish before striking
• Polished dies — the dies are polished to produce mirror-like fields on the coin
• Frosted devices — the raised design elements on the dies are treated (sandblasted or chemically etched) to produce a frosted, sculpted appearance on the coin
• Multiple strikes — each coin is struck two or more times at lower speed with higher pressure, ensuring every detail of the design is fully impressed
• Individual handling — proof coins are handled with gloves, individually inspected, and packaged in protective capsules or cases

The result is a coin with mirror-like reflective fields and sharply detailed frosted design elements — the "cameo" or "ultra cameo" effect. Proof coins are produced in limited quantities, sold at significant premiums above face value, and intended solely for collectors.

Reverse proof

The opposite of a standard proof: the fields are frosted and the design elements are mirrored. This creates a distinctive inverted contrast effect. Reverse proofs are produced occasionally as special editions and can command high premiums for their unusual appearance.

Piedfort

A coin struck on a planchet that is twice the standard thickness, and therefore twice the standard weight. Piedforts are typically produced in proof quality and in much smaller quantities than standard proofs — often only a few thousand compared to tens of thousands for regular proofs.

The thicker planchet produces a more substantial, weighty coin with a sculptural quality that standard-thickness coins lack. Piedforts are among the most expensive products a mint offers for any given design. The word comes from the French "pied fort" meaning "strong foot" or "heavy weight."

Comparing striking standards

Historical minting techniques

Before modern mechanised minting, coins were produced by quite different methods. The Technique field in Zenkasu records which method was used.

Hammered (before ~1660)

The oldest method. A blank was placed on a lower die (the anvil die) and the upper die was struck with a hammer. This produced coins with uneven shapes, off-centre designs, and variable thickness. Most ancient and medieval coins were hammered. The irregular edges made it easy for people to clip small amounts of metal from the coins — one of the reasons milled edges were eventually introduced.

Milled (1660 onwards)

Machine-struck coins produced on a screw press or later a hydraulic press. "Milled" refers to the mechanical process rather than the edge treatment, though milled coins often do have milled (reeded) edges. Milled coinage is far more uniform in shape, weight, and design placement than hammered. Virtually all coins produced since the late 17th century are milled.

Cast

Metal poured into a mould rather than struck between dies. Used for the earliest coins in China and some ancient Greek and Roman coins. Cast coins have a distinctive porous texture and lack the sharp detail of struck coins. Casting is sometimes used for modern medals and art pieces, but it's also the most common method for producing counterfeits — a cast fake typically has a softer, slightly mushy appearance compared to a genuine struck coin.

Mint errors

Despite rigorous quality control, mistakes happen during the minting process. Genuine mint errors are highly sought after by a dedicated community of error collectors. The most common types include:

Die errors

• Doubled die — the die itself received a doubled impression during its manufacture, causing doubling in the lettering, date, or design on every coin struck from that die. The 1955 US doubled die cent is perhaps the most famous example.
• Die crack — a crack in the die surface creates a raised line on the coin. As the die continues to wear and crack, the lines become more pronounced.
• Die clash — the obverse and reverse dies strike each other without a blank between them, transferring faint ghost images of one side's design onto the other die.

Planchet errors

• Wrong planchet — a blank intended for one denomination is accidentally fed into the press for a different denomination. A dime struck on a cent planchet, for example.
• Clipped planchet — the blanking punch overlaps with a previously punched hole in the metal strip, producing a blank with a curved bite taken out of the edge.
• Lamination — a flaw in the metal strip causes a thin layer of the surface to peel away, leaving a flaky or peeling area on the coin.

Strike errors

• Off-centre — the blank wasn't properly seated in the collar when struck, causing part of the design to be missing. Described as a percentage (10% off-centre, 50% off-centre).
• Multiple strike — the coin was struck two or more times, with the blank shifting between strikes. This produces overlapping doubled images.
• Brockage — a previously struck coin sticks to one of the dies and acts as a die itself, impressing a mirror-image copy of its design onto the next blank.
• Mule — a coin struck with mismatched dies, such as an obverse from one denomination and a reverse from another. Extremely rare.