Dies experience many forms of brittle failure. The most common form is the die crack — a fracture line that crosses the die face. The length, width, shape, trajectory, and end points of die cracks vary quite a bit. 

Many die cracks extend in from the edge of the die and end blindly somewhere in the field and design. Some die cracks extend between two points on the edge. Median or bisecting rim-to-rim die cracks divide the die face into equal or sub-equal portions. And blind-ended die cracks begin and end in the middle of the die face.

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Most collectors are familiar with die cracks that spread apart. When this occurs, coin metal rises into the resulting crevice, forming a ridge. The illustrated 1976 Mexico 5-peso coin displays a number of wide, intersecting die cracks that weave through the periphery of the reverse face.

Bi-level die cracks

Slightly less common are bi-level die cracks. Such cracks are characterized by vertical displacement instead of lateral spread. In other words, one side of the crack sinks down, producing a sharp step. The obverse face of a broadstruck 2014 India 5-rupee coin shows a profusion of bi-level die cracks (along with a few narrow cracks of the conventional sort). The cracks are abundant enough, severe enough, and extensive enough to warrant the label “shattered die” for this error.

Bi-level die cracks can occur only in the presence of subsurface deformation. In such dies, a hard, brittle exterior encloses a softer interior, which undergoes plastic deformation instead of cracking.

Horizontal offset

A rarer and more subtle manifestation of subsurface deformation beneath a cracked surface is horizontal offset. In such errors, one side of the crack slides along the other side, producing a discontinuity in contiguous portions of the design that cross the crack. 

Shown here is a 2002 Brazil 10-centavo coin with a shattered obverse die. The obverse face shows many forms of brittle failure — several cuds or “corner die breaks,” several retained interior die breaks, and many conventional and bi-level die cracks. A thin die crack of the conventional sort passes through the L of BRASIL. But in addition to lateral spread, the area shows horizontal offset. The back of the L is shifted down relative to the front of the letter.

As this feature demonstrates, different forms of crack displacement can co-occur, either in the same spot or at different points along the same die crack. For example, a conventional die crack can gradually transform into a bi-level die crack along its route. A die crack can likewise exhibit both lateral spread and vertical displacement in the same area. I suppose if you look hard enough you can find cases where all three forms of displacement appear together in the same spot.

Spreading and sliding

Spreading and sliding movements tend to be more exaggerated in the case of severe rim-to-rim die cracks, asymmetrical split dies, and retained cuds. A retained cud is a die fragment that is physically separate from the die neck but which is held in place (usually by the collar). Diagnosing a retained cud is always fraught with uncertainty, unless the amount of vertical displacement or horizontal offset is grossly exaggerated (see the Jan. 24, 2011, and July 8, 2013, Collectors’ Clearinghouse columns). These two sliding movements have traditionally been used to diagnose retained cuds, but as we’ve noted, they’re not exclusive to these forms of brittle failure.

An example of such uncertainty can be found among the nine or 10 shattered obverse (anvil) dies for the 2007-P Roosevelt dime that are recorded. Most of these incorporate a large retained cud in the southern hemisphere (see previous references). These retained cuds show vertical displacement along all or most of their route. Horizontal offset is also sometimes observed. 

Despite appearances, I suspect that many or perhaps all of these “retained cuds” were never truly detached from the die neck. Nevertheless, I won’t quibble with the retained cud diagnosis as there is no way to tell what was happening beneath the surface of the die.