Laboratory X-ray powder diffraction is a very effective and non-destructive method for direct phase analysis of paint layers usually consisting of complicated mixtures of pigments, binders, dyes, fillers and/or degradation products. While a conventional Bragg-Brentano set-up allows direct non-invasive analysis of smaller painted objects, e.g. miniature portraits, a micro-diffraction mode plays a substantial role in the analysis of samples (usually smaller than 1 mm) taken from paintings. The application of mineralogical analysis for study of provenance and technology of late Gothic/early Renaissance painting materials as well as examples of uncovered degradation products will be presented. The methodological pros and cons will be also discussed.