Results are given for surfaces of roughness 3 μ in., 115 μ in. and anodized aluminium within the wavelength range 1 to 14 μ. The spectral emissivity varied strongly with surface roughness and oxidation, but only slightly with temperature. Typical values at wavelengths 2 and 8 μ respectively were 0.09 and 0.04 for polished, 0.30 and 0.24 for roughened, 0.30 and 0.20 for anodized aluminium. Natural oxidation slightly increased the spectral emissivity at all wavelengths below 9 μ and had a marked effect between 10 and 12 μ. An anodic oxide film increased the spectral emissivity beyond 10 μ to greater than 0.70. The significance of these variations to radiation pyrometry is briefly discussed.