Measurement methods are known for determining the concentration of an ingredient in a body of ceramic or glassy material, in which the optical path length or the signal propagation time of a measurement wave penetrating the body of ceramic or glassy material in a measurement direction is determined and evaluated. Starting therefrom, in order to indicate a non-destructive method for determining a concentration of an ingredient in a body of ceramic or glassy material, which is also suitable for measurement in the production process of the body concerned, it is suggested according to one embodiment that modulated gigahertz radiation is used as the measurement wave.