## 2 Materials and Methods  
The two buildings in calcarenite studied in this work are made of stones, sourced from the same local quarry as required by the research project [13; 14], closely located in the rural site of Basilicata, shown in Figure 1, not far geographically from Matera. The procedures for the collection, storage and preparation of samples for XPS analysis were based on the guidelines of the ISO committee 20579-1:2024 available online: [[https://www.iso.org/standards.html](https://www.iso.org/standards.html)]([https://www.iso.org/standards.html](https://www.iso.org/standards.html)) (consulted from the publication date 2024-09, accessed on 3 July 2025). Adequate quantities of powdered samples were gently scraped from the wall surfaces of the cubic building (occasionally added to small fragments eventually detachable after years if suitable in size for the insertion into XPS sample holders), mainly from the upper half zones of each wall to avoid traces of soil contaminants, at regular time intervals  
Figure 1: A new calcarenite cube built adjacent to an old calcarenite farmhouse, both located in the municipality of Lavello (Pz) in the Gravetta District between the archaeological park ‘Forentum romana’ (III-I century BC, south east) and the industrial site ‘Fenice’ (Incinerator \(\leftrightarrow\) waste-to-energy plant nowadays owned by Rendina Ambiente srl, north west). of outdoor exposure at 0 (unexposed reference sample, OR), 3, 6, 9, 12, 21 and 52 months. The 52-month period seemed appropriate for long-term sampling, given the slowing of surface changes already observed as the second year approached, and indeed, the five-year span proved to capture both the rapid initial phase and the subsequent stabilization. Similar sampling procedures that include samples collection, storage and cataloguing, as reported in Figure 2, were performed on the entirely preserved NE walls of the old farmhouse, selecting different colored zones:  
1. Calcarenite-like surface (Blank color renewed by wind and rain erosions)
2. Efflorescent-like surface (whitish)
3. Green mossy surface
4. Black crusty surface  
Brief overview of spectroscopic and microscopic techniques relevant to this work  
X-ray Photoelectron Spectroscopy (XPS) ensures to determine the outer layer composition of solid surfaces, i.e., within a vertical depth of 10 nm using the conventional X-rays sources of ~1500 eV energy, here reported. Importantly, it provides joint information on the elements present and their chemical state by measuring the binding energy (BE) of the emitted photoelectrons and, by resolving the peak components via curve-fitting, the semi-quantitative analysis of the identified surface compounds.In summary, XPS provides detailed chemical information of the analyzed samples and interfering contaminants due to its surface sensitivity. It requires ultra-high vacuum (UHV) conditions and has limitations in depth profiling and spatial resolution. The bulkier spectroscopy XRD (X-ray Diffraction) provides structural information of solid materials from depths of several microns, depending on the X-ray source. The diffractometer characteristics are reported previous work [13], and the results obtained on the powdered samples are here recalled for comparison, taking into account thatonlycrystalline (inorganic) compounds can be revealed by X-ray scattering. A quite large amount of materials is required to produce the diffraction pattern, and mixtures of crystalline and amorphous phases can be difficult to interpret. Scanning Electron Microscopy equipped with Energy-Dispersive Spectrometry for microanalysis (SEM/EDS) allows the morphological images (at various magnifications) of samples (in powders or thin sections) and to measure the X-ray emitted by elements from depths of a few microns for their identification and relative intensity.