This study is devoted to the experimental and analytical investigation of the mechanism underlying the formation of the ‘black crackle’ decorative effect on the surface of ceramic glaze, which arises as a result of the thermochemical transformation of a bio-derived organic precursor under oxygen-limited conditions. The aim of the study was to assess the influence of the thermal conversion products of the bio-precursor on the phase composition, microstructure, local distribution of elements and optical properties of the ceramic glaze, as well as to establish the mechanism underlying the formation of the decorative effect. The experimental programme was initially planned using the Taguchi approach; however, the processing conditions were subsequently adjusted based on preliminary experimental observations. The resulting samples were analyzed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray analysis (SEM–EDS), and spectrophotometric measurements using the CIELAB system. The results of X-ray diffraction analysis (XRD) showed that the decoration process did not lead to any significant change in the composition of the main crystalline phase of the glaze. FTIR spectroscopic analysis revealed chemical changes consistent with the thermal transformation of the bio-derived precursor. SEM–EDS observations revealed local differences in the detected carbon signal at selected microzones of the craquelure network; however, carbon coating and the limited number of measurement points prevent the distribution of precursor-derived carbonaceous material from being established directly. Spectrophotometric results confirmed a reduction in brightness and an increase in the total color difference in the decorated samples. Taken together, the results indicate that the black crackle decorative effect is associated with optical changes in the glazed surface rather than a detectable change in the main crystalline phase composition of the glaze. The possible contribution of carbon-rich thermally transformed material in selected crack regions remains a proposed mechanism requiring further verification. The proposed approach opens up new scientific and technological prospects for the use of bio-waste as a functional precursor in the decoration of ceramic surfaces.

This study is devoted to the experimental and analytical investigation of the mechanism underlying the formation of the ‘black crackle’ decorative effect on the surface of ceramic glaze, which arises as a result of the thermochemical transformation of a bio-derived organic precursor under reducing conditions. The aim of the study was to assess the influence of the thermal conversion products of the bio-precursor on the phase composition, microstructure, local distribution of elements and optical properties of the ceramic glaze, as well as to establish the mechanism underlying the formation of the decorative effect. The experimental programme covered various combinations of temperature, storage time and the amount of bioprecursor, using the Taguchi method. The resulting samples were analyzed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray analysis (SEM–EDS), and spectrophotometric measurements using the CIELAB system. The results of X-ray diffraction analysis (XRD) showed that the decoration process did not lead to any significant change in the composition of the main crystalline phase of the glaze. FTIR spectroscopic analysis revealed chemical changes consistent with carbonization resulting from the thermal degradation of the bioprecursor. SEM-EDS observations showed that the carbonized products are distributed unevenly across the entire surface and are mainly localized in individual microzones of the craquelure network. Spectrophotometric results confirmed a reduction in brightness and an increase in the total color difference in the decorated samples. An integrated analysis of the results showed that the black crackle decorative effect is formed not through the formation of a new crystalline phase, but through the local accumulation of carbonized products in specific areas of the crackle network—products formed as a result of the thermochemical transformation of the bio-precursor under reducing conditions—and the optical contrast created thereby. The proposed approach opens up new scientific and technological prospects for the use of bio-waste as a functional precursor in the decoration of ceramic surfaces.

The possibility of producing cellular glass using volcanic ash has been studied by considering the chemical and mineralogical composition of volcanic ash from the Molladag deposit. It was found that it contains aluminosilicates and is represented mainly by quartz, feldspar and amorphous phase. The optimal composition and the main technological parameters of thermal treatment of mixtures of volcanic ash (window glass production waste and volcanic ash) borosilicate frit together with a gas-forming agent were determined. To further optimise the experimentally observed composition and process regimes, an appropriate regression equation adequately describing the process was derived using the second order orthogonal rotatable plan available in the literature. A comparative X-ray phase analysis of the thermal processing products with the raw mixture was carried out and it is shown that the mineralogical composition of the cellular glass is represented mainly by the glass phase, feldspar and the newly formed mineral wollastanite.