The presence of radiating lines on a coin is an indication that something was wrong with the die, the planchet, or the strike. Often, a collector assumes that the exact cause can be assigned to all examples they encounter. That would be a mistake.
By far the most common cause of radiating lines is die deterioration (die fatigue, die wear). As a die strikes hundreds of thousands of coins, the die face is slowly remodeled. One change that often occurs is the development of shallow radial grooves. These naturally appear on the coin as low ridges that extend outward from the center of the coin. Hobbyists call these radial flow lines. I’ve shared here a 1988-P dime struck from a heavily worn obverse die.
Radial flow lines cover most of the surface and are best developed in the field, which is typical. The reverse face (not shown) lacks radial flow lines and shows few signs of die wear. This probably means the reverse die was swapped out while the obverse die remained in place. A less likely possibility is that the obverse die deteriorated more rapidly than the reverse die.
Radial flow lines vary quite a bit in thickness. Some are much thicker than the lines on this dime, while others, like those seen on a 2007-P dime [Above Right] are much thinner.
A far less common cause of radiating lines (at least on business strikes) is the development of a “starburst” pattern in the field. Starburst is most commonly found on proof coins. Shown here is a 2000-P Sacagawea dollar with starburst on both faces.
Starburst is often mistaken for thin radial flow lines. However, starburst lines are thinner than the thinnest radial flow lines and show no detectable relief. Moreover, they develop in early die states (EDS), as shown by this dollar coin. This would indicate they are unrelated to die wear.
For many years I was unsure about the cause of starburst. I speculated that it could be caused by the breakdown of a surface die coating or the outward migration of microscopic particles. Pete Apple dug into the phenomenon and unearthed research by Roger Burdette. Burdette received an explanation from George E. Hunter, the U.S. Mint’s Assistant Director for Process and Quality Control. Hunter asserted that, “The starburst effect is caused by abrasive particles that build up and then etch the die as they are carried outward from a central point in the direction of metal flow during successive strikes.” It would therefore appear that starburst is not a property of the die, per se, but of microscopic grains that cling to the die face. The nature of this microscopic grit and where it might originate isn’t explained.
Apple discovered that many proof dies are retired prematurely due to starburst. I refer to Apple’s October 14, 2025 post on Joe Cronin’s Facebook group, where he provides a link to his research on the phenomenon.
Confusion arises when starburst – or what appears to be starburst – is found in association with later die states. A second 2000-P Sacagawea dollar shows a starburst pattern similar to the first specimen. In this case, however, both dies show evidence of wear consistent with a middle die state (MDS).
There are three possible interpretations:
(1) Starburst is, in fact, a form of die deterioration;
(2) Microscopic particles responsible for this case of starburst didn’t infiltrate the striking chamber until later in the life of these dies;
(3) Starburst developed early in the life of these dies and was not erased by later die wear.
The peripheral field of a 1994-D 5-cent coin displays radiating lines that resemble starburst. The lines vary in width and tend to flare out as they approach the design rim.
Since they show clear relief, it’s almost certain that this is another case of die deterioration. However, I can’t entirely rule out the possibility that these radial lines were generated by the migration of particles larger than those responsible for classic starburst. I hold out this possibility because some of the ridges show a corrugated texture while the intervening field is smooth. The rough texture could conceivably have been caused by grit migrating and chewing its way across the die face.
Some forms of die damage take the form of radiating lines. Shown here is a 2000-D half dollar with a spray of raised, radiating lines and bumps that extend outward from a smoother central zone located approximately between GOD and the underside of Kennedy’s throat.
The corona formed by these lines may represent damage incurred as fine particles migrated outward from the central point. Alternatively, all the lines could have been etched into the die face in a single moment when the obverse die collided with, and shattered, a brittle foreign object. The main objection to both scenarios is that the greatest damage should be located in the center of the corona.
Some struck-through errors take the form of radiating strips of altered reflectivity. In a July 1, 2023 post on Joe Cronin’s Facebook group, Charles Bud Schatz posted images a 2007 George Washington dollar with radiating bands that appear brighter than the surrounding field.
These bands appear on both faces and vary enormously in width, with some appearing recessed. This points to the presence of a foreign substance that was stuck to the die face and that gradually migrated outward. The material would presumably be a thin layer of lubricant with relatively low viscosity.
In other words, these types of radial lines would fall under the umbrella category of “grease strike”. The term “grease” is applied to a wide variety of coatings that accumulate on the die face. These vary considerably in thickness, texture, and viscosity.
There are many types of alterations and accidental post-strike damage that produce radiating lines. Chemical and mechanical methods are both involved, sometimes at the same time. A good example of post-strike radial lines appears on a 1974 half dollar that was posted about two years ago on Reddit [click here]. The radial lines appear to have been scratched into the coin’s surface.
Radial lines also appear on an 1853 Large Cent that appeared in a January, 2014 Heritage auction and that was labeled by NGC as “obverse half of split planchet”. It’s clear that, rather than being an error, the obverse face was attacked by a corrosive agent. The denticles provided a pathway that allowed the presumed acid to eat into the coin’s surface in such a way as to produce a radial pattern of grooves and ridges.
On April 29, 2025, the coin’s owner Jack Young, solicited comments about the coin on Joe Cronin’s Facebook group. After the coin was universally panned, Young cracked it out. He discovered that it was undersized, with a diameter of 25 millimeters instead of the expected 27.5 millimeters. Acid-soaked coins are usually reduced in diameter. Young later posted photos of an undersized 1837 cent with the same type of acid damage, including the radial lines.
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