Plaster casts...kind of

This is my first attempt at pushing a cardboard tube into clay, TRYING to get that outer texture on the cardboard rings KEPT on the outside, even in a plaster replication.

On one side, is a flattened surface where I had poured the plaster into the mold and wiped it away to create the holes. I want to keep this flattened side on the inside and the nice textured side on the outside. Proving difficult.