What is that on the reverse!

[Coriel]

Hi Everyone
I'm not sure if I'm on the right thread, but here goes. Last year I was on a dig in a local village and we found about half a dozen coins in a ditch, mostly of Valens. They were filed away. Yesterday I asked to see them and review them with my new found - ahem - expertise. To my astonishment I found a Constans coin amongst them, really quite fine, but what intrigued me, and is the point of this post, is the reverse. I think you'll be able to see that it is a head, presumably of Constans, although there is no inscription that I could make out. What happened here? an accident? Perhaps it is quite common in LRBs? Also saw that the dreaded bronze disease had taken hold,  so it will be rushed to a conservator to see what he can do.
James

[Victor]

this is called a brockage, which happened when a coin stuck to the die which resulted in the next coin struck bearing an incuse design of the stuck coin. This usually happened with the upper die (which struck the obverse) since it was harder to notice a stuck coin on the top die than on the bottom die.

While not that common, they are not that rare either, here is a Constantine II that I saw for sale today.

I don't think that it has bronze disease, only a flaky patina. Corrosion has gotten under the surface and started de-laminating the top portion.

[Coriel]

Thanks Victor, I wondered whether it was something like that. A new word for me, - Brockage!
James