Spectral-directional emittance measurements of aluminum oxide (99.5% pure), in air, were performed at 823 K using an apparatus comprised of a Fourier Transform Infrared (FTIR) spectrometer, a blackbody radiating cavity (hohlraum), and a sample holder which allows directional measurements. The data cover a wide spectral range between 2 and 25 mu m, and a directional range from a surface normal to a 72 degrees polar angle. The aluminum oxide sample used in the experiment had a nominal surface roughness of 1 mu m determined by a profilometer. Directional emittance shows no departure from dielectric behavior.