BaF2 is transparent from the ultraviolet to the infrared, from 150-200nm to 11-11.5μm, and can be used as a material to make optical components such as lenses. It is used in windows for infrared spectroscopy, in particular in the field of fuel oil analysis. Its transmittance at 200nm is relatively low (0.60), but at 500nm it goes up to 0.96-0.97 and stays at that level until 9μm, then it starts falling off (0.85 for 10μm and 0.42 for 12μm). The refractive index is about 1.46 from 700nm to 5μm. Barium Flouride is used as a preopacifying agent and in enamel and glazing frits production. It is also used in metallurgy, as molten bath for refining aluminum.