INVESTIGATION OF DUST PRESS PRACTICE AS INFLUENCING FINISHED SIZES AND CRACKING

Owing to erratic firing behavior, the factors affecting finished sizes of ware were investigated. Uneven distribution of air and water content and uneven density produced irregular shrinkage and consequent cracking and warping. The percentage of water in the clay as pressed is shown to be the dominant factor as affecting shrinkage. Suitable loading of die corrected the differential shrinkage. Experimental procedure is detailed. Influence of rate of pressing on porosity is set forth.     

MECHANISM OF PLASTICITY FROM COLLOID STANDPOINT1

Introduction .—Brief statement of present conceptions of the colloid chemists. Theory .—Plasticity is caused by the, enveloping film of colloidal material which surrounds the clay grains, this film being of opposite polarity to the grain proper. Addition of electrolyte acting as deflocculant causes outer layer of film to be attracted to ion of same polarity as clay particle, thus reducing effective diameter and increasing polarity of plasticity inducing particles. Particles which were held by surface forces of “particles in contact” are no longer in contact and are actually repelling each other due to like and increased polarity. A flocculating ion drives action in opposite direction causing an increase in depth of colloid film thereby increasing surface in actual contact and decreasing repulsive force of plasticity inducing particles. Transport numbers as well as polarity are governing factors in ions of electrolytes. Measurements .—Touch method is proven to be unreliable. Desirability of a unit of measurement. Plea for a unit of colloidality and standard method for measurement.     

KILN MANIPULATION IN RELATION TO SCHOOL AND STUDIO POTTERY1

A suggestion for a chart to be used in connection with the firing of studio and school kilns. The use of the chart makes it possible to record the time element, amount of fuel, and the temperature curve.