Investigators fabricated a series of briquettes from commercial clays, incorporating the following tempering materials in quantities of 40% and 80% by original weight of clay and in coarse and fine grades: sand, unburned shell, and burned shell. A pendulum test and a simplified quench test were conducted on tempered and untempered, fired briquettes to measure resistance of impact and thermal shock. Based on test results, the authors concluded that the use of finely-ground tempers in general and burned shell in particular produce briquettes that are significantly more durable than briquettes incorporating other materials. -- AATA