Code and data sharing are crucial practices to advance toward sustainable archaeology. This article explores the performance of supervised machine learning classification methods for provenancing archaeological pottery through the use of freeware R code in the form of R Markdown files. An illustrative example was used to show all the steps of the new methodology, starting from the requirements to its implementation, the verification of its classification capability and finally, the production of cluster predictions. The example confirms that supervised methods are able to distinguish classes with similar features, and provenancing is achievable. The provided code contains self-explanatory notes to guide the users through the classification algorithms. Archaeometrists without previous knowledge of R should be able to apply the novel methodology to similar well-constrained classification problems. Experienced users could fully exploit the code to set up different combinations of parameters, and they could further develop it by adding other classification algorithms to suit the requirements of diverse classification strategies.

Hexagonal neo-formed crystallites have been observed in thin section of different medieval and post-medieval lead-glazed ceramics. Although they are clearly visible in thin section using plane polarized light, their plate shape makes them barely seen on the polished cross sections. Basal sections have never been found on the polished sections and only few transversal very thin sections could be seen. In this case, the morphology resembles acicular and it is not possible to analyze them properly by SEM–EDX because the crystals are very thin and the glaze surrounding is analyzed as well. Micro-Raman microscopy was carried out directly on the polished thin sections. This technique allows specific areas as small as 1 μm in diameter to be analyzed and it is able to characterize inclusions that are not found on the glaze surface. However, the wavenumber features observed cannot be assigned to a specific compound. The thickness of the crystallites (a few hundred nanometers) seems to be responsible for the low sensitivity of the Raman instrumentation. 15 × 15 μm² micro-X-ray diffraction patterns using synchrotron radiation (SR-μXRD) in transmission geometry were obtained from the crystals using the same thin section preparation. SR-μXRD was able to localize the crystallites and avoid the overlapping signals corresponding to other mineral phases. In this way, the hexagonal crystallites present in the glaze have been unambiguously identified as hematite crystallites. Finally, some replications were made under laboratory-controlled conditions to determine the firing conditions in the formation of those crystallites. The presence of hematite coexisting with melanotekite indicates a firing temperature 925°C

During the last thirty years, microstructural and technological studies on ceramic glazes have been essentially carried out through the use of Scanning Electron Microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). On the contrary, optical microscopy (OM) has been considered of limited use in solving the very complex and fine-scale microstructures associated with ceramic glazes. As the crystallites formed inside glazes are sub- and micrometric, a common misconception is that it is not possible to study them by OM. This is probably one of the reasons why there are no available articles and textbooks and even no visual resources for describing and characterizing the micro-crystallites formed in glaze matrices. A thin section petrography (TSP) for ceramic glaze microstructures does not exist yet, neither as a field of study nor conceptually. In the present contribution, we intend to show new developments in the field of ceramic glaze petrography, highlighting the potential of OM in the microstructural studies of ceramic glazes using petrographic thin sections. The outcomes not only stress the pivotal role of thin section petrography for the study of glaze microstructures but also show that this step should not be bypassed to achieve reliable readings of the glaze microstructures and sound interpretations of the technological procedures. We suggest the adoption by the scientific community of an alternative vision on glaze microstructures to turn thin section petrography for glaze microstructures into a new specialized petrographic discipline. Such an approach, if intensively developed, has the potential to reduce the time and costs of scientific investigations in this specific domain. In fact, it can provide key reference data for the identification of the crystallites in ceramic glazes, avoiding the repetition of exhaustive protocols of expensive integrated analyses.

Galena, also known as PbS, was widely used in the production of lead glazes from the beginning of the 18th century to the second half of the 20th century. Although the PbO‐SiO ₂ system has been studied for years, the PbS–SiO ₂ phase diagram, involved in the formation of a glaze with galena, has not yet been investigated. Temperature transformations for the system 75 wt% PbS‐25 wt% SiO ₂ are investigated in a high‐temperature resolved X‐ray diffraction experiment with synchrotron radiation and compared to those of the equivalent system 70 wt% PbO‐30 wt% SiO ₂ . Lanarkite, PbO·PbSO ₄ , is the phase predominantly formed as soon as galena decomposes during the heating. The results show that the system melts at a temperature higher than the PbO–SiO ₂ system, but far lower than those expected for the PbO–PbSO ₄ –PbS system. A historical misfired lead glaze produced with galena is also studied. The presence of galena, lanarkite, and mattheddleite, Pb ₁₀ (SiO ₄ ) _3.5 (SO ₄ ) ₂ Cl _2, is determined and discussed in terms of the composition of the galena mineral used and the firing conditions in light of the high‐temperature transformations previously obtained.