Error Coin Essentials: Plastic Deformation

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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 a wide variety of examples, error coins remain one of the hobby’s most engaging fields. 

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In my previous column, I discussed some of the ways in which die steel can crack and break apart. Less appreciated are the ways in which dies can experience plastic deformation.

Plastic Deformation 

Plastic deformation is distinct from the surface remodeling that dies experience over time. Referred to as “die deterioration,” “die wear,” and “die fatigue,” surface remodeling involves the migration of metal atoms. Letters and numbers typically widen, design details become mushy, and the die face may develop radial flow lines or an orange-peel texture. Plastic deformation refers to large-scale movements of metal in the horizontal and vertical plane that alter the topography of the die face, rearrange its features, or erase its details.

Types of Deformation

Some types of plastic deformation are common. Shown below is a 1994 cent with a partial “ridge ring” that extends counterclockwise from 1:30 to 7 o’clock. Here, the surface of the die sank in, creating a channel that cuts through IN GOD WE TRUST. Other zinc cents exhibit a swollen field behind or in front of Abraham Lincoln’s bust. Ordinarily soft, zinc is tough on dies because it stiffens up under rapid compression. These patterns of deformation are less common on other denominations.

Atypical forms of die deformation (“die deformation errors”) can be traced to abnormally soft die steel. This can be caused by improper heat treatment (annealing, tempering, and quenching), poor quality steel, or using the wrong grade of steel. Die deformation errors usually form early in the press run and then quickly stabilize. They are often localized, with the center of the die face most often affected.

Die Subsidence Errors

The illustrated 1943-S quarter above shows a well-known die deformation error. The area of the die face in the vicinity of George Washington’s throat collapsed, forming a “goiter.” The letters of IN GOD WE TRUST nearest to the swelling are italicized. Another so-called “goiter” appears on the 1924-S cent below, although it more closely resembles a distended external jugular vein. Both swellings can be considered “die subsidence” (sunken die) errors.

Die subsidence errors are frequently found in association with split dies. The 1965 dime below was struck by an obverse die with an enormous median split, which is also straddled by a very prominent die subsidence error. It seems counterintuitive that brittle failure and plastic deformation should co-occur, but it happens quite often. For example, most purported retained die fragments (aka “retained cuds”) are not really detached from the die face but instead reflect surface cracking and subsurface plastic deformation. An example appears on the reverse of the 1965 quarter, also shown below.

Some die deformation errors affect the entire die face. This 2016-P Harpers Ferry quarter below shows a grossly distorted reverse design. The deformation developed quickly and then stabilized. Meanwhile, the obverse die (not shown) has no evidence of die wear.

Design Creep

A distinctive form of die deformation affects the single 2014-P 5-cent reverse (hammer) die below. Referred to either as “design creep” or a “flared die face,” the die face expanded early in the press run and then stabilized. As a result, the peripheral letters hug or run off the edge of the coin. The center of the design also has an odd custard-like texture.

The range of die deformation errors is far wider than can be explored in this short article. But they all show that, despite its hardness, die steel can sometimes behave like putty.

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Mike Diamond has been collecting, researching, and writing about error coins since 1997.  He previously wrote a weekly column for Coin World  (“Collectors’ Clearinghouse”) that focused 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.

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