The Roman site at Makariopolsko village in Northeastern Bulgaria has been identified as a ceramic production center, featuring single- and double-chamber kilns, abundant ceramic material, and a nearby water source. Geological assessments also reveal local clay deposits. Previous archaeological studies have noted similar Roman production sites in the region, primarily focusing on the study of the kilns and the macroscopic description and classification of the ceramics. However, there has been a lack of research into the pottery’s composition and the sourcing of raw materials, which is essential for understanding the area’s cultural and economic context. This study aims to determine the raw material and firing temperature of the ceramic from the site at Makariopolsko village. Clay samples (both raw and fired at 1100 °C) and ceramic were subjected to chemical, statistical, phase X-ray structural, and thermal analyses. The findings indicate the use of calcareous illite–kaolinitic clay, sourced locally, with an added sandy component. The ceramics were fired at temperatures of 570–760 °C and 920–945 °C. These results, which support the site’s identification as a pottery production center, highlight advanced pottery skills and the dual functional capabilities of the kilns. Additionally, they pave the way for further research into regional production center relationships.

One trend in the development of building materials is the partial or complete replacement of traditional materials that have a high carbon footprint with eco-friendly ecological raw materials and ingredients. In the present work, the influence of replacing cement with 10 wt% thermally activated natural zeolite on the structural and physical-mechanical characteristics of cured mortars based on white Portland cement and river sand was investigated. The phase compositions were determined by wavelength dispersive X-ray fluorescence (WD-XRF) analysis, X-ray powder diffraction (PXRD), diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS), and scanning electron microscopy (SEM), as well as thermogravimetric analysis simultaneously with differential scanning calorimetry (TG/DTG-DSC). The results show that the incorporation of zeolite increases the amount of pores accessible with mercury intrusion porosimetry by about 40%, but the measured strengths are also higher by over 13%. When these samples were aged in an aqueous environment from day 28 to day 120, the amount of pores decreased by about 10% and the compressive strength increased by nearly 15%, respectively. The microstructural analysis carried out proves that these results are due to hydration with a low content of crystal water and the realization of pozzolanic reactions that last over time. Replacing some of the white cement with thermally activated natural zeolite results in the formation of a greater variety of crystals, including new crystalline CSH and CSAH phases that allow better intergrowth and interlocking. The results of the investigations allow us to present a plausible reaction mechanism of pozzolanic reactions and of the formation of new crystal hydrate phases. This gives grounds to claim that the replacement of part of the cement with zeolite improves the corrosion resistance of the investigated building solutions against aggressive weathering.

The production and trade of metals was the foundation of the economic wealth of many regions in the world, which makes the study of ancient metallurgical slags of primary importance. This type of study is relatively new for Bulgaria, where research in the field started in the late 1960s with chemical analysis of copper ore, slags, tools and finished goods from the ancient copper mine in the Ay-bunar area. Iron is one of the most commonly found elements in the earth’s crust and its deposits are widespread, including on Bulgaria’s territory. To this day, however, the study of iron slags from Bulgarian sites through chemical and phase analysis has almost never been explored. The application of these methods allows for the determination of the technology of the ancient metallurgical process. This study investigates iron slags from two Bulgarian archaeological sites, situated in close proximity to the Sarnevets hematite ore deposit, Sarnena Sredna Gora mountain. The ore bodies of the deposit outcrop on the earth’s surface and can be easily recognized due to the red coloring of the soil around them, which is a characteristic trait for finding iron deposits. In addition to the ancient mining activities in the region, proven by over 20 registered ancient mine workings, ancient metallurgical activities were established as well, as proven by the discovered slags. A sample from the hematite ore was studied along with the slags, so that the percentage of iron extracted during the metallurgical process can be determined. The samples were studied through X-ray fluorescence analysis, powder X-ray diffraction analysis, and Mössbauer spectroscopy. The obtained results show that the slags are of the “furnace bottom slags” type, which is a product of metallurgical activity achieved through bloomery technology. The temperature range of the furnaces was determined to be around 900–1100 °C. The reduction of iron was possible at such low temperatures due to the ore’s type—self-fluxing hematite ore. The percentage of iron extracted from the ore was calculated to be between 3.39% and 8.65%. Additionally, a relationship was established between the percentage of extracted iron, the Fe²⁺ content included in wüstite, and the viscosity index of the liquid slag. The acquired results are new to the archaeological studies conducted on Bulgaria’s territory and are a prerequisite for future interpretation and archaeological research.

In this study, high-energy milled (HEM) samples of natural phosphorites from Estonian deposits were investigated. The activation was performed via planetary mill with Cr-Ni grinders with a diameter of 20 mm. This method is an ecological alternative, since it eliminates the disadvantages of conventional acid methods, namely the release of gaseous and solid technogenic products. The aim of the study is to determine the changes in the structure to follow the solid-state transitions and the isomorphic substitutions in the anionic sub-lattice in the structure of the main mineral apatite in the samples from Estonia, under the influence of HEM activation. It is also interesting to investigate the influence of HEM on structural-phase transformations on the structure of impurity minerals-free calcite/dolomite, pyrite, quartz, as well as to assess their influence on the thermal behavior of the main mineral apatite. The effect of HEM is monitored by using a complex of analytical methods, such as chemical analysis, powder X-ray diffraction (PXRD), wavelength-dispersive X-ray fluorescence (WD-XRF) analysis, and Fourier-transformed infrared (FTIR) analysis. The obtained results prove the correlation in the behavior of the studied samples with regard to their quartz content and bonded or non-bonded carbonate ions. After HEM activation of the raw samples, the following is established: (i) anionic isomorphism with formation of A and A-B type carbonate-apatites and hydroxyl-fluorapatite; (ii) solid-phase synthesis of calcium orthophosphate-CaHPO₄ (monetite) and dicalcium diphosphate-β-Ca₂P₂O₇; (iii) enhanced chemical reactivity by approximately three times by increasing the solubility via HEM activation. The dry milling method used is a suitable approach for solving technological projects to improve the composition and structure of soils, increasing soil fertility by introducing soluble forms of calcium phosphates. It provides a variety of application purposes depending on the composition, impurities, and processing as a soil improver, natural mineral fertilizer, or activator.

This work studies burned clay plasters from archaeological sites in the cultural-historical region of Sarnena Sredna Gora Mountains and their southern foothills. It was established that the plasters have a similar phase composition, consisting of montmorillonite, muscovite, illite, quartz, albite, calcite and microcline, which indicates that the employed construction system drew resources from a common source or several. Different firing temperature ranges were determined – up to 500 °C; between 500–700 °C; and above 700 °C – up to calcite decomposition temperature (<800 °C). The assumed high temperatures confirm the burning of the archaeological structures, and the varying temperature ranges can be explained by the uncontrollable conditions during the fire.