'Die crazing' leaves coins with spiderweb of die cracks
- Published: Feb 9, 2014, 7 PM
The surfaces of hard, brittle objects can sometimes develop a meshwork of fine cracks that don’t necessarily compromise the structural integrity of the object.
The phenomenon is known as crazing.
Pottery glazes frequently develop crazing, especially with age. Polymers such as polycarbonate plastic also have a tendency to craze.
Crazing can also affect the working face of a coinage die, although it’s a rare and poorly understood phenomenon. As with any form of brittle failure, the root cause could be selection of the wrong grade of steel, excessive carbon in the alloy, a heavy impurity load, the presence of microscopic voids, or improper die preparation (annealing, tempering, quenching).
Since dies have a tendency to develop cracks, crazing is not a completely surprising phenomenon. The difference is that ordinary die cracks are at least fractionally wider than craze lines and don’t form a dense network.
Two rather different-looking examples of crazing are presented here.
Our first specimen, a 1964 Kennedy half dollar, comes from Lee Lydston. It shows crazing on both faces and largely confined to the field.
Crazing is rather dense to the left and right of Kennedy’s head and on either side of the eagle. The coin does show conventional die flow lines, indicative of a later die state.
Some of the die flow lines extend perpendicularly from craze lines, suggesting that the fine cracks either interrupted the formation of the flow lines or, alternatively, facilitated their appearance.
Our second specimen, an Uncirculated 1943-D Lincoln cent, comes from Robert (“BJ”) Neff. Craze lines are restricted to the obverse face and mainly appear on the raised design. Most of the craze lines are located on Lincoln’s coat, while a few run across his head.
At a macroscopic level, the craze lines pursue a very uneven course that resemble wool fibers. At a microscopic level, the craze lines are exceptionally “wiggly,” somewhat like dry ramen noodles.
While conventional die cracks will often follow an uneven path, they are nowhere near as tortuous as these fine cracks.
The 1943-D cent also shows fine raised concentric lines on the obverse face that are best seen in the center. These are concentric lathe marks. After machining, the cone-shaped head of the blank, working die is supposed to be polished smooth.
If this step is skipped or performed in a slipshod manner, the grooves left by the lathe will persist, even after hubbing. There is no reason to suspect that the concentric lathe marks are related to the crazing.
Crazing not ‘shattered die’
Crazing should not be confused with shattered dies. While shattered dies are highly variable in appearance, what unites them is the presence of numerous intersecting die cracks.
These die cracks can be of the conventional sort, with the sides of the crack spread apart, leaving a raised line on the coin. They can also be bilevel die cracks, where one side of the crack sinks in, leaving a corresponding step on the surface of the coin.
Shattered dies can show a mixture of the two forms of die cracks.
The illustrated 2007-P Roosevelt dime was struck by a shattered obverse die. It is one of at least nine shattered obverse dies known for this year and Mint mark.
Numerous die cracks (mostly bilevel) cross the lower half of the obverse design. The difference from the two specimens struck by crazed dies is readily apparent.
The die cracks in this dime are more prominent than in either specimen. They are longer and much less numerous than the craze lines in the half dollar. They are less tortuous than the craze lines in the 1943-D cent. The die that struck this 2007-P dime was heading toward failure.
Indeed, increasingly severe signs of brittle failure are documented in three later die stages.
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