The principles underlying emissivity measurements in solid materials at temperatures in the range of 3500 K, and conditions for carrying out these measurements are briefly reviewed. The advantages of using an imaging furnace for this application are pointed out and the necessary optical system described. The function of the shutter for separating emitted and incident radiation, control of the temperature by the aperture-limiting cylinder, and the calibration of a spectrometer by a black-body reference standard are explained.