Nuclear techniques and techniques using ionising radiation represent a valuable tool in non-destructive diagnostics applied to geology, geophysics, archaeological findings and objects of arts, particularly for determining the composition of materials used in the production of artefacts. X-ray fluorescence analysis is one of the most widespread methods using ionising radiation for studying the elemental composition of materials. It is frequently used for analysing various cultural and historical relics and objects of art. The paper describes the author’s experience with X-ray fluorescence analysis in investigating historical relics namely by means of portable spectroscopic devices. The use of these methods is demonstrated by the example of the investigation of fresco paintings.