Colour Transformation and Textural Change in Biotite: Some Remarks for the Interpretation of Firing Technology in Greyware Pottery Thin-Sections

Firing is a crucial step in the production of pottery, as it irreversibly transforms the clay into ceramic. Clay sintering and subsequent vitrification occur during firing, together with other transformations undergone by specific minerals and rock inclusions according to their optical and physical properties, including their colour. Some of these are visible in thin-sections and might be interpreted as technological markers or contribute to the estimation of firing temperatures, although most of them are poorly documented. In this paper, we approach the transformations in colour, texture and optical properties that occurred in biotite inclusions from medieval greyware pottery. Our study considers a batch of 40 pottery samples from medieval Catalonia analysed by XRD. According to the estimated firing temperature ranges and atmospheres, we examined the behaviour of biotite at different temperature ranges from 700 °C to 1000 °C by means of optical microscopy, considering its size, shape and abundance, and compared these features to a wider assemblage of thin-sections from medieval earthenware. The results obtained are interesting, as they offer a valuable reference for petrographic studies on pottery. We discuss the potential of ceramic petrography as a way to perform more precise and refined sample selection for further analysis on archaeothermometry.

Density and thermal expansion of borate and borosilicate glass-forming melts

Density, molar volume and thermal expansion of borate and borosilicate melts are properties that significantly affect the process of forming composite coatings by slip-firing technology. Based on experimental data on the density of glass-forming melts, adequate generalizing mathematical models have been developed by using the method of multiple correlation; these models describe the dependence of the molar volume (VT) of alkaline borate, alkaline silicate and multicomponent melts on their oxide composition and temperature with a standard deviation of (0.22–0.27) cm3 mol–1. The regression equation has the following general form: VT=A(xi)–B(xi)/T, where xi is the content of an oxide, T is the temperature, subscript "i" stands for the number of an oxide concerned. The changes in volumetric coefficient of thermal expansion (CTE) of the molten glasses are analyzed as functions of both temperature and chemical composition. It should be noted that borate melts in comparison with silicate ones have much higher values of CTE. The highest value of CTE of experimental melts is observed at glass transition temperatures (Tg). An increase in the temperature above Tg contributes to a significant decrease in CTE. An increase in the content of alkali metal oxides in most glass-forming melts results in an increase in the values of CTE.

Understanding the Potential of Bio-Carbon Capture and Storage from Biomass Power Plant in Indonesia

Indonesia is currently experiencing a significant increase in population, industrialization and energy demand. As the energy demand increases, so does the production of climate-altering CO2 emission. Biomass power plants have emerged as a low carbon power generation alternative, utilizing agricultural and industrial waste. Biomass power plants have the potential of being a carbon-negative power generation technology in the near future by integrating carbon and capture storage (bio-CCS). The objective of this paper is to analyze and map potential CO2 emission in the processes of biomass power plants from gasification and firing or co-firing technology, then recommend suitable carbon capture technology based on the biomass power plant characteristics in Indonesia. The CO2 emission to be captured in the gasification process is 11-15% of the producer gas, while in co-firing it is 7-24% of the flue gas stream. Using biomass instead of coal in power plants reduces the electric efficiency and increases the plant’s in-house emission, but when analyzed in a wider boundary system it is apparent that the net GWP and CO2 emission of biomass power plants are way smaller than coal power plant, moreover when equipped with carbon capture unit. Biomass power plant that uses firing technology can reduce CO2 emission by 148% compared to typical coal power plant. Installing carbon capture unit in biomass firing power plants can further reduce the specific CO2 emission by 262%. If carbon capture technology is implemented to all existing biomass power plants in Indonesia, it could reduce the greenhouse gas emission up to 2.2 million tonnes CO2 equivalent annually. It is found that there are 3 significant designs for gasification technology: NREL design, Rhodes & Keith design and IGBCC+DeCO2 design. The first two designs are not suitable to be retrofitted into existing biomass power plants in Indonesia since they are based on a specific BCL/FERCO gasifier. While IGBCC+DeCO2 design still needs further study regarding its feasibility. While for firing, the most promising technology to be applied in the near future is solvent-based absorption because it is already on commercial scale for coal-based power plants and can be implemented for other source, e.g. biomass power plant. Bio-CCS in existing biomass power plant with firing technology is likely to be implemented in the near future compared to the gasification, because it applies the post combustion capture as an “end-of-pipe” technology which is generally seen as a more viable option to be retrofitted to existing power plants, resulting in potentially less expensive transition.

The microstructure of multicolor hare’s fur glaze: the correlation between morphological and compositional characteristics and glaze color

The hare’s fur glazed Jian wares characterized by radial fur-like strips, as one of the typical representatives of Chinese ceramics in the 10th-13th century (A.D.), were famous for the aesthetic values in highlighting the color sparkling effects of tea soup, which were one of the indispensable tea wares in tea culture. The firing technology of hare’s fur glaze of Jian wares not only played a crucial role in the development of Chinese ceramic history, but also enlightened the modern imitation technology. The hare’s fur glaze of Jian wares can be further grouped according to the color of strips, of which the yellowish-brown hare’s fur glaze (yellowish-brown matte strips), gold hare’s fur glaze (golden shiny strips) and silver hare’s fur glaze (bright silvery strips) were the most representative types. Epsilon-Fe2O3, a specific metastable crystal phase, has become a research hotspot as the chromogenic crystals of hare’s fur glaze, however, the comparative analysis focused on the correlation between ε-Fe2O3 and the macroscopic glaze color has been barely reported. In our work, the bright color strips (hare’s fur area) and black strips (black glaze area) of silver, gold and yellowish-brown hare’s fur glaze were morphologically and compositionally analyzed by SEM and EDS, respectively. The morphological features and compositional differences of three representative types of hare’s fur glaze samples were summarized, which indicated the differences in the size, distribution and coverage of crystals and the distribution and contents of materials. It was speculated that high-level of Fe2O3 and CaO with low-level of SiO2 and Al2O3 may relate to the crystallization of ε-Fe2O3. This work helps in laying the foundation of further explanation of the technological differences of hare’s fur glazes.

Terminal Classic Interactions between the Western Petén Lakes Chain and the Western Lowlands

Innovations in a poorly known Terminal Classic pottery type, Jato Black-on-Gray (JBG), at sites around Lake Petén Itzá include use of gray slips and the presence of monkey and ik’ motifs. They appear on local forms (cylinders, plates) and are particularly associated with burials. These suggest emulations of varied gray ware pottery in the western and southwestern lowlands, such as Chablekal Fine Gray. JBG thus supports inferences based on other data (architecture) of ties to these regions, including in-migration into the lakes area, featuring a reworking of the new (motifs; firing technology) with the old (forms). The western lakes area was part of a larger ceramic system in the western lowlands, suggesting that Terminal Classic pottery makers were engaged with innovations in a thriving “business.”