Error Coin Essentials: How Errors Are Struck

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Error Coin Essentials introduces the core concepts behind coins that didn’t come out quite right. These articles provide a practical foundation for collectors who want to understand how errors happen, how to identify them, and how to collect them. With strong collector demand and wide variety, error coins remain one of the hobby’s most engaging fields. 

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Experience has taught me that any component of a coin press that is bolted down, screwed in, soldered into place, or belongs to a single-piece unit can come loose or break free. This malfunction creates fascinating collectibles—error coins.

This article focuses on errors that involve the hammer die, the anvil die, and the collar. The hammer die delivers the impact to the planchet, while the anvil die receives the impact. The collar is the retaining ring that keeps the coin from expanding beyond the diameter stipulated for each denomination. Depending on the time period, the obverse die or the reverse die can function as the hammer die. Both setups were employed in certain years.

The hammer die, anvil die, and collar have been in use for well over 200 years.  I suppose the modern configuration was established when steam-powered coining presses replaced screw presses in 1836.  That year also featured the introduction of the tightly confining “closed collar.” A looser “open collar” was employed before then.  The latter was simply used to keep the blank more or less centered between the dies. 

Hammer Die Errors

It’s well known that the hammer die (or hammer die assembly) can shift laterally, generating a horizontal misalignment. These can range up to 50 percent of a coin’s diameter, although most examples are much smaller. Shown here is a weakly struck 2000-D cent that was struck by a hammer (obverse) die with a 29-percent horizontal misalignment and a rotation or pivot of 23 degrees.

It’s often assumed that the anvil die is more likely to rotate, as a loose anvil die cannot fall out of its recess the way a loose hammer die can. However, analysis of multi-error rotated die errors (like our 2000-D cent) shows that it is almost always the hammer die that rotates.

Standard references omit pivoted die errors, although the hammer die assembly is certainly capable of spinning around an eccentric axis of rotation. Pivoted die errors are sometimes impossible to distinguish from errors that combine a die rotation with a horizontal misalignment.

Additionally, standard error references omit major vertical misalignments of the hammer die. Also called tilted die errors, these involve the hammer die or its assembly tilting relative to a vertical axis. Shown here is a 1972-D half dollar in which the hammer (obverse) die was elevated at its left pole and rotated 90 degrees.

Anvil Die & Collar Errors

While collars are capable of tilting a few degrees (as in the case of tilted partial collar errors), I’ve yet to see a coin struck by a strongly tilted anvil die. But the potential exists.

Though most major horizontal misalignments involve the hammer die, a small percentage involve the anvil die. This might seem surprising, as the neck of the anvil die is closely surrounded by the collar, and many people think the collar is incapable of lateral movements. A horizontal misalignment of the anvil die can occur only if the collar shifts laterally (carrying the anvil die with it) or if the collar breaks apart, freeing the anvil die of its embrace. Shown here is a 1993-P quarter dollar with a dual (bifacial) misalignment that incorporates a 6.2-percent south-to-north misalignment of the anvil (reverse) die and a modest southeast-to-northwest misalignment of the hammer (obverse) die. A strong collar scar along the southern perimeter of the reverse face shows that the collar was intact. All major anvil die misalignments are unavoidably broadstruck (struck out-of-collar).

Not only can collars shift laterally, but they can also rotate. A rotating collar was detected in a large series of 2002-P half dollars struck by four different die pairs. By tracking a collar chip, I showed that the collar rotated in a mostly clockwise fashion through well over 360 degrees (Coin World, April 20, 2020).

Conclusion

These press components are capable of additional acrobatics in all three planes of motion and all three axes of rotation.  The results can be quite surprising and eye-catching.

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Mike Diamond has been collecting, researching, and writing about error coins since 1997.  Since November 2009, he has written a weekly column for Coin World (Collectors’ Clearinghouse) that focuses on minting errors and die varieties.  Prior to that, he was responsible for dozens of articles that appeared in CONECA’s specialty journal Errorscope.  He created and contributed most of the content found in The Error-Variety Ready Reference.  Over the past 28 years, he has discovered or described well over 100 new error types.