CaLa2S4 is a member of the family of ternary sulfides. It has the cubic Th3P4 structure, space group I-43d, with both cations on equivalent 8-coordinated sites. Powders prepared by firing oxides and carbonates in flowing H2S can be processed by a combination of hot-pressing and hot-isostatic pressing into sulfide ceramics with good infrared transmission. The vibrational absorption edge is at 17 μm. The materials are resistant to attack by water. The microhardness of the nearly 100% dense ceramics is 600 kg/mm2. Optical transmission of 55% (including reflection losses) at 14 μm has been achieved, but optical quality is extremely sensitive to processing conditions. Absorption and scattering are produced by residual pores, by second phase impurities on grain boundaries, by oxidation products such as sulfate and thiosulfate, and electronic defects arising from non-stoichiometry.