Ultra-black etched electroless nickel plate was developed by the National Bureau of Standards as a high absorption solar collector surface finish. This etched electroless nickel was plated on different surfaces and substrate materials for which such quantities as bi-directional reflectance, total integrated scatter, absorptivity and emissivity were measured. Temperature cycling, outgassing and adherence were investigated. These experimental data were used to determine the suitability of this etched nickel plate as a baffle coating. This finish is unsuitable for infrared applications. Investigations at BASD are being conducted to extend the suitability of this surface finish to the infrared. Investigations are not considered complete; however, major improvements in the etched nickel process indicate potential for a suitable baffle coating for a majority of applications. The solar emissivity has been preserved, while greatly enhancing the room temperature emissivity.
George I. Geikas,
"Scattering Characteristics Of Etched Electroless Nickel", Proc. SPIE 0384, Generation, Measurement and Control of Stray Radiation III, (4 October 1983); doi: 10.1117/12.934932; https://doi.org/10.1117/12.934932