Effect of plastic materials on engobe characteristics. I. Type of clayey material.

One of the major ceramic engobe constituents is the clayey material. This m aterial contributes suitable properties to the engobe suspension for correc t application and yields an unfired layer with adequate mechanical strength and bonding to the body. A series of tests was conducted in the present st udy to determine how the type and proportion of clayey material affected en gobe suspension properties (rheological behaviour) and resulting unfired en gobe layer properties (compactness, bonding and surface drying time). The t ested clayey materials were of the type normally used for engobe preparatio n: white clay, kaolin and bentonite. It was found that all the studied engobe characteristics varied considerabl y on modifying the type of clayey material. The arising variations were sho wn to be due to changes in engobe plasticity and unfired layer packing on c hanging the type of clayey material.