Due to high interest among DIY-ers in extruders for clay i posted a simple but robust and durable desigh, based on easily available standard components. Assembly requires minimal toolset. Please find more details at https://www.stoneflower3d.com/projects/clay-extruder-prototype/
I built a prototype of the clay syringe pump some time ago, and yesterday was printing with this. Volumetric feeding is something excellent. Stable and accurate with no worries about safety and extrusion speed. But requires some initial test printing (2-10 g of clay) to reach "working pressure" in the pump. Here is the setup.
More images and discussion see here: https://plus.google.com/u/0/communities/103324258900608601175