If sampling follows the non-invasive research performed in ALMA, it is much more efficient and targeted. Micro-samples are standardly prepared in the form of cross-sections (embedded in polyester resin) and the stratigraphy of layers is studied by optical and electron microscopes (combining images collected in visible light, UV light, and back-scattered electrons). The high quality of micro-photographs guarantees that the stratigraphy will be correctly described and that the thin and fragmentary layers will not be overlooked.