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Mike Diamond

Mike has been collecting, researching, and writing about error coins since 1997. He has published hundreds of articles in Coin World, Errorscope, and other numismatic publications. He is the primary source of information that appears in the online error/variety reference error-ref.com. He previously served as President of CONECA and has an active online presence
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Recent Articles by this Author

This breakaway aluminum feeder finger was struck by 2007-D cent dies. Photos courtesy of Heritage Auctions.

Signs of Feeder Contact Surprisingly Rare on Off-Center Strikes

Errors and Varieties Mike Diamond -
By Mike Diamond Off-center strikes are the result of a malpositioned coin metal disc (planchet or coin). A faulty feeder/ejector mechanism is presumably responsible for...
Mikw Diamond Article on lines

Radiating Lines On Coins Have More Than One Cause

US Coins Mike Diamond -
The presence of radiating lines on a coin is an indication that something was wrong with the die, the planchet, or the strike. Often,...

Bifacial Collar Clash Seldom Encountered

US Coins Mike Diamond -
Collar clash is a phenomenon that, until relatively recent times, was almost wholly restricted to the hammer die. A typical collar clash occurs when a...
This is an image of an off-center 1952-D cent with a striated crescent surface, likely caused by a rolling mill issue.

A Third Ridged 1952-D Lincoln Cent Points to a Rolling Mill Error

US Coins Mike Diamond -
By Mike Diamond for CoinWeek... In the February 14, 2022, "Collectors’ Clearinghouse" column in Coin World, I discussed an off-center 1952-D Lincoln Cent that displayed...
This is an image of a 1970-D Lincoln Cent with a lamination error.

Planchet’s Depression Linked to Embedded Contaminants

US Coins Mike Diamond -
By Mike Diamond for CoinWeek... There are many ways foreign (or foreign-looking) material can end up in a coin. It might have been present in...
Figure 5. This triple-struck quarter dollar shows a normal first strike, a very weak 40% off-center second strike, and a very strong 70% off-center third strike. All strikes were delivered by the same die pair and are die-struck on both faces. The black arrow points to a struck-through error that occurred during the second strike.

Weak Strikes Can Co-occur With Any Kind of Striking Error

US Coins Mike Diamond -
By Mike Diamond for CoinWeek... Weak strikes on planchets of normal thickness are primarily the result of two proximate causes. The most frequent is an...
Figure 6. This 1887 Peru un sol was counterstamped by a pair of 1894 Guatemala 1/2 real dies. Unlike the previous coins, this secondary strike was sanctioned by the government.

Discs Carrying Undersized Coin Designs Arise in Two Ways

Collecting Strategies Mike Diamond -
by Mike Diamond for CoinWeek... Planchets and blanks struck by dies belonging to smaller-size denominations are always, or almost always, the result of backroom shenanigans....
This broadstruck, copper-alloy cent features a full, centered, first-strike brockage of the reverse design on its obverse face. The incuse, mirror-image design is complete, except for a fadeout of the letters comprising UNITED STATES.

Peripherally Incomplete Centered, Circular Brockages Warranted Investigation

US Coins Mike Diamond -
by Mike Diamond for CoinWeek... When a coin (or other die-struck object) is struck into a blank disc of metal (planchet), the incuse, mirror-image design...
Figure 1. The obverse face of this uncirculated 1983 Lincoln Cent carries the incuse letters of TRUST. Lying in the field next to the design rim, these letters are best interpreted as contact marks from another cent. Photos courtesy of Cliff Reuter.

A Forensic Analysis of Faint Incuse Letters on a 1983 Lincoln Cent

US Coins Mike Diamond -
by Mike Diamond for CoinWeek… On June 21, Cliff Reuter posted images of a 1983 Lincoln Cent showing the upper portions of an incuse, mirror-image TRUST between the...
Figure 1a,b.  This off-center Egypt 25 piastres coin was overstruck by a pair of 2010 Egypt 50 piastres dies within a 50 piastres collar.  The host coin’s struck tab was thinner than the minimum die clearance, explaining the lack of a secondary impression.  (All images show the reverse face of the final strike in its actual orientation relative to the obverse face.)

Defaced Dies Used to Strike Egyptian Coins and Planchets

World Coins Mike Diamond -
by Mike Diamond for CoinWeek... A defaced die is one whose design has been ground off, melted, or removed by a milling machine. This procedure...
This slightly off-center 1998-P quarter dollar shows trans-strike damage on its obverse face.  The unstruck crescent and the newly-struck design were both heavily scraped in the same area and in the same direction by the same moving machine part. Image: Mike Diamond / CoinWeek.

Mint Mishaps : Four Quarters Show Trans-Strike Damage

US Coins Mike Diamond -
by Mike Diamond for CoinWeek... Understanding Mechanical Damage A blank, planchet, or coin can suffer mechanical damage at many points during minting. The specific culprit responsible...

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