Now, here's the setup for a die clash. What happens here of course is that the dies first strike each other without a
flan in place, meaning that the dies impact each other rather than a
flan, resulting in damage to the dies. Typically this results mostly in damage to the upper (
reverse) die only, with it taking an impression of the lower die. This is what I'm depicting with the
red parts on the diagram.
Presumably the reason it's normally the
reverse die that gets damaged is because of the asymmetry between the
reverse and
obverse designs ... The
reverse design, being typically more spread across the
flan, means that the force of the strike if fairly evenly spread across the die. The
obverse design, being a
head, means the the central portion of the die is always sunken and therefore the force of the strike is transmitted mostly by the surrounding perimeter of the die, hence the pressure
per unit
area will be greatest in this region.
We can see from the diagram what this might be expected to look like. The central portion of the
reverse die is spared, but the perimiter is damaged, with the center-perimiter
border being defined by the shape of the
bust on the
obverse die. When a coin is now struck with these damaged dies it might be expected to look like the one in the diagram, with the central portion of the
reverse looking normal, a center-perimeter
border defined by an
incuse impression of the
bust, and a perimeter that may have flattened detail relative to the center.
Of couse this is only the general case, but the same rationale would apply to other situations where maybe there's only a small
bust or a large central design (sunken on die) on the
reverse die (therefore causing die clash damage more to the
obverse die rather than
reverse).
(cont)