Abstract: A probe (1) is used to measure the dielectric properties of rigid or semi-rigid materials (4), for example, works of art. The probe comprises an inner conductor and an outer, coaxial, conductor separated by a layer of insulator e.g. Teflon (TM). The probe is coupled to a network analyzer (11), which provides microwave frequency radiation which is transmitted by the probe onto the surface of the material where it is reflected back from the surface back down the probe to the analyzer, where it is analyzed to give measurements on the dielectric properties of the material. The probe typically has an outside diameter of around 0.86 mm, and because of its size allows measurements to be made, non-invasively, and in real time on small areas of material. The outside diameter can be made of the order of microns by selecting the frequency of the radiation, which allows measurements to be made in a sample of a semi-rigid material e.g. a layer of paint for depth profiling.