The invention relates to a method for optically monitoring the progression of a physical and/or chemical process taking place on a surface of a body in which the surface radiation which emanates from part of the surface during the physical and/or chemical process, is measured with the aid of a measuring device, in particular a sensor. In order to develop a method of this kind such that sintering processes can also be monitored in a firing furnace having thermal radiation equilibrium, the invention proposes to emit the radiation (14) having a radiation spectrum that differs from the surface radiation, to the surface (10) by means of a radiation source (15) and to measure the radiation with the aid of a measuring device (16).