Ceramic Printing WASP Extruder
Liquid Deposition Modeling - http://www.wasproject.it/w/ldm-liquid-deposit-modelling-wasp-extruder/
The above page shows a good design rationale for the clay extruder, though extruder is shot load, not continuous load for the press part. Here is a PDF archived - File:LDM.pdf
Unfortunately, not OSHWA Compliant.