I think we're talking about a dip mould, here.
I had a brief technical chat with Patrick Hogan, Ray Annenberg, Eddie King and Nashie at the Whitefriars Day at Aaronson Noon back in March, and one of them said that was the most commonly used mould for the kind of shape and finish being discussed here.
Eddie had with him a diamond point mould that he uses to create bubbled pieces. Patrick had helped recreate a tricorn mould so that Ray could show us how those vases were made. It was all fascinating stuff.
I'm sure that one of the above could contribute more - or Adam, perhaps. I'm just extrapolating from my very limited knowledge base (but I want to learn more...).