Fake piastre casting mold

I bought this unusual thing from a coin dealer in Saigon. He told me that some farmer had found it in the ground.
I was showing this artifact to many experts, including Howard Daniel, and they all believe it's authentic.

It is made of soft metal looking like zinc, so it could not be a mold itself.
I believe this thing was an intermediate step in forgery producing technology.
Unfortunately, I don't know any details of this technology.
Any comments would be appreciated...