Measurements of the optical constants and thermal radiative properties of high‐temperature solid tungsten and molten aluminum have been made using a new instrument that includes two independent optical systems and surface control and analysis capability. The two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity, operate over the wavelength range 0.4–10 &mgr;m with sample temperatures between 940 and 1630 K. The surface science capabilities of the instrument permit the preparation of high‐purity samples of known compositioninsitu. The apparatus includes two 5‐keV argon‐ion sputter guns, an ultrahigh vacuum pumping system, and an Auger spectrometer. The two sputter guns allow surface cleaning to occur while optical measurements are being made, or while Auger spectroscopy is determining the surface composition of solid or liquid samples. The ellipsometric optical system uses a novel radiation source (a carbon composite element), refractive optics (calcium fluoride), interference filters for spectral selection, and both calcite and wire grid polarizers to cover the extended wavelength range. The system for measuring the normal spectral emissivity uses reflective optics and an integral blackbody cavity that is located in the wall of the crucible holding the liquid sample. The use of two measurement techniques gives independent determinations of the normal spectral emissivity and thus allows reliable estimation of experimental errors.