A conformal antireflective coating of WO3 on a textured tungsten surface is found to significantly increase the optical absorptance of the surface over a broad selected band of wavelengths. The coating enhances the selectivity of solar absorbing surfaces on dendritic tungsten and increases the solar absorptance of such surfaces. The average solar absorptance measured at air mass 2 was increased from 0.95 to 0.985 for large dendrite surfaces and from 0.76 to 0.90 for small dendrite surfaces. Emittance values for the anodized surfaces at 300âÂ°C range from 0.18 for the small dendrites to 0.5 for the larger dendrites. The WO3 conformal coating, produced by anodization of the tungsten, forms an antireflective coating with a minimum at a wavelength between 0.43 and 0.8 Î¼ for anodization voltages between 20 and 40 V, respectively. Total reflectances as low as 0.00025 have been measured. © 1978, American Institute of Physics. All rights reserved.