Abstract: A spark plug is described for Otto-cycle engines having a metallic spark plug body, having a center electrode, having a ceramic insulator, which is arranged between the center electrode and the body and is based on aluminium oxide, and having at least one earth electrode. The invention provides for the insulator to be composed of 0.01% by weight to 1% by weight of magnesium oxide, at most 0.3% by weight of natural and/or impurities, with the rest being aluminium oxide, and being formed by solid-phase sintering so that it is very largely free of glass phases.

Abstract: A process for the thermal tempering of glass wherein the hot glass is immersed in a vessel in which there are two mutually immiscible liquids. The liquid of lower density is above the liquid of higher density. The glass is precooled for a specific time in the liquid of lower density and then is brought into the liquid of higher density.