The study concerns the optical and structural properties of layers obtained by a new efficient surface treatment totally free of chromium species. The process is made up of an anodic oxidation of copper in an alkaline solution followed by an alkaline potassium permanganate dipping post-treatment. Coatings, obtained at the lab and pilot scales, are stable up to 220 degrees C in air and vacuum, present low emissivity (0.14 at 70 degrees C) and high solar absorptivity (0.96), i.e. a suitable thermal efficiency (0.84 at 70 degrees C).