Evolution of the infrared emissivity of Ni during thermal oxidation until oxide layer opacity

•The emissivity of Ni was measured in situ throughout the whole oxidation process.•Complex emissivity evolutions depending on the wavelength and oxide layer thickness.•A crucial effect of the oxide layer on the radiative properties is observed.•Decreasing temperature dependence of the total emissivity of strongly oxidized Ni.•A way to investigate the emissivity of oxidizing metals is presented.