an improvement in a method of extruding a plasticized inorganic powder mixture having a plasticizing organic binder carried in an aqueous vehicle , by passing the mixture through an extruder and then through a die to produce an extrudate . the improvement involves homogeneously blending in the extruder as part of the mixture , carbon dioxide in the supercritical and / or liquid form , to lower the viscosity of the mixture and produce an extrudate that is stiffer in a shorter time than it would be , absent the carbon dioxide , without increasing the extrusion pressure .