Commercial solar absorbers of nickel pigmented anodized aluminium are composed of an inner nickel pigmented sublayer of about 0.3 mu m thickness and a 0.4-0.5 mu m thick top layer of plain alumina. Thermal emittance can be reduced from 0.17 to 0.12 if the top layer is made thinner, to be about 0.1 mu m. The solar absorptance is 0.96 as for the thicker coating. In this study degradation is analysed for samples with thin or thick alumina top layer after exposure to elevated temperature, 300-500 degrees C, or humidity. The results from these tests show that a thinner aluminium oxide top layer has the same durability as a thicker top layer. The implication of making commercial nickel pigmented anodized aluminium with an oxide half as thick as today is a reduction of the anodization time to about half the time and lower manufacturing costs.