Discontinuity in normal spectral emissivity of solid and liquid copper at the melting point

Normal spectral emissivities for solid (ɛ_λ,solid) and liquid (ɛ_λ,liquid) copper at the melting point have been determined, and the discontinuity in ɛ_λ,liquid and ɛ_λ,solid at the melting point has been discussed. The spectral emissivity was determined by comparing the spectral radiation intensity of the sample to that of the fixed-point blackbody over the wavelength range 550 to 750 nm. The samples and fixed-point blackbody were heated in the continuous casting type cold crucible. Values of ɛ_λ,liquid and ɛ_λ,solid at 650 nm were 0.167 and 0.108, respectively. The emissivity ratio of ɛ_λ,liquid/ɛ_λ,solid increased from approximately 1.2 to 1.8 as the wavelength increased in the range 550 to 750 nm. The discontinuity in ɛ_λ,liquid and ɛ_λ,solid at the melting point has been qualitatively explained by the optical absorption mechanism due to the intraband transition.