Elemental composition of the pigment grains in the layers is usually determined by scanning electron microscope coupled with energy dispersive X-ray microanalysis (SEM-EDS), which has better spatial resolution than the laboratory micro-XRF. However, when comparing the results of XRF (performed on objects) and SEM-EDS (performed on micro-samples), it is always necessary to take into account the differences in detection limits and ranges. In ALMA, micro-samples are analysed in low vacuum mode (without the need to metallize and, subsequently, regrind their surface that causes loss of valuable material). Wavelenght-dispesive X-ray spetroscopy (WDS) detector can be alternatively used to detect low element contents