It’s not unusual for copper-plated zinc cents to develop semi-circular ridges just inside the design rim. Although they seldom form a complete circle, these acknowledged manifestations of die deterioration were nevertheless called “ridge rings” by longtime Clearinghouse columnist Eric Von Klinger.
Ridge rings occasionally crop up among older, copper-alloy cents and among other denominations.
Superficially similar rings can be found among world coins. While they seem to be a form of die deformation, I’m not convinced that die wear is responsible. Many of the rings are found on Italian fractional euro coins. A typical example is seen here in an Italian 2002 10-cent coin. Each face shows a complete ring that is tall, narrow and sharply defined. Design elements like stars and lines continue on top of the ring, demonstrating that the ridge is not intrinsic to the design.
In a posting to the Combined Organizations of Error Collectors of America Error-Variety Coin Forum, Italian collector “andrea78ts” observed that the rings are common among Italian fractional euro coins, and that they pre-date introduction of the euro.
Sharply defined rings exist on other world coins. The illustrated Irish 1996 5-penny coin has a complete ring on each face. The rings are relatively flat and slope downward toward the field. Unlike the Italian coin, the rings on the Irish coin hug the internal margin of the design rim.
Our final ringed coin is an aluminum-bronze 25-satang coin of Thailand that appears to have been struck in 1998. On the obverse face, the ring varies a bit in thickness and in the extent to which it approaches the design rim. On the reverse face, the ring is well-separated from the design rim. A second 25-satang coin in my collection (not shown) has much thinner rings.
Ridge rings on domestic coins are highly variable in length, height and width and typically show softer external and internal margins than the rings on foreign coins.
Domestic ridge rings are often associated with other signs of die deterioration such as an orange peel texture and radial flow lines. The Italian and Thai examples show no independent signs of die deterioration. The Irish example does show significant die wear and evident breakdown of the chrome plating on the die face. However, there’s no guarantee that any of this is related to ring formation.
The uniformity, completeness, clarity, high relief, early appearance and bifacial presence of these rings suggest that we might be dealing with an etiology unrelated to die wear. Let me suggest a few possibilities.
It’s possible that the rings are present at installation and develop during hubbing. It may be that the working hub was too soft (or the working die too hard), and this caused complimentary peripheral deformation of both cylinders. Under this scenario, the working hub would have developed a circular ridge and the working die a circular trough.