Abstract: Polycrystalline optical materials formed from halides of alkali and alkaline-earth metals and of other metals, and mixtures thereof, some of which contain selected additives to act as nucleators and grain-growth regulators, and also apparatus and method of producing these materials from a liquid melt are disclosed. The polycrystalline products have optical transmissions approaching those of single-crystal materials, but exhibit significantly higher resistance to thermal and mechanical shock.The disclosed method and apparatus allows formation of unshattered polycrystalline ingots of any desired size by uniform nucleation from a homogeneous melt, and involves the controlled uniform removal of heat from the solidifying mass alone or in combination with a continuous addition-solidification process, which results in the formation of a substantially clear polycrystalline body or ingot, free of voids, and composed of randomly oriented single crystal having grain growths in a range of from about 0.01 to 10 mm.