Fluorine-doped tin dioxide layers were produced by spraying an organic tin solution onto a hot substrate. The substrates were common window glass, pyrex and black enamelled steel. Best results were obtained with black enamelled steel, in which case typical values of the spectral selective layers were: a solar absorptance of 0.92 and a thermal emittance of 0.15. Investigations of the optical and electrical properties show that optical behaviour in the 3–10 µm region conforms well to the Drude theory. Ageing tests were carried out in air and in vacuum. In vacuum above about 250°C ageing effects occur, which are related to a decrease of the SnO-fraction of the layer. The effect of sodium, which can diffuse from the glass substrate into this layer, was also investigated. Experiments show that only unrealistically high concentrations of sodium show significant changes in the properties of the layer.