Here is a nice example of a sunken die on the reverse of a 1972D Ike dollar. The area to the right of the crack is actually raised slightly over the area on the left. The raised area on the coin is the sunken area on the die. The photo shows lighting from the left and from the right.
The term I've used is "bi-level die crack", but regardless of what you call it, it is rather unusual.
I think a "bi-level die crack" sounds pretty good. I guess a sunken die doesn't necessarily need to be cracked, while this name would imply a sunken die with a die crack, and that describes this piece precisely. Cool!
I wrote an article recently in Errorscope dealing with "sunken dies", or what I have referred to as "die subsidence". In such errors, parts of the die face sink in and this may or may not be accompanied by cracking. I also treated related errors such as bi-level die cracks and retained interior die breaks. I've got a second article coming out soon on the subject of die subsidence and its relatives.
