An approach to the dynamics of clay firing

Archaeological ceramic amphorae from underwater marine environments: Influence of firing temperature on salt crystallization decay

“…27 At lower firing temperatures (800ºC) the individual mineral temper grains are easily distinguishable from the 8 clay matrix; at higher firing temperatures (1000º-1050ºC) the sintering process produces an increase in the interconnection among these grains and the matrix and the porosity decrease. 28,29 The clast grain size distribution is mainly bimodal in Italic and Tarraconensian samples ( Fig. 3b and 3c, respectively) with prevalence of both larger and smaller quartz aggregates.…”

“…4c) which may denote firing temperatures above 900ºC. 27,29,[44][45][46] However, as was mentioned before, in this case diopside seems to come from the raw material and not developed during firing. The absence of illite and the presence of gehlenite, wollastonite and, in a lower extent, anorthite and diopside in the samples is a consequence of the reactions occurring when calcium or magnesium-rich clays are fired above 900ºC.…”

The historical glazed tiles from Nossa Senhora da Soledade Cemetery, Northern Brazil: microstructural, physical and mineralogical characterization

“…In the results of the mineralogical characterization of ceramic parts, it was possible to observe the presence of minerals belonging to the raw material and formed by the firing because of mineral transformations that occur with increasing temperature [15,[20][21][22]. The mineralogical variety of samples indicated that the raw material of the samples was composed primarily of quartz, calcite and/or dolomite, hematite or goethite, and clay minerals, such as kaolinite, common results for Portuguese samples from the nineteenth century [16].…”

“…The incidence of these two contrasting structures (according to their fusion point) in the paste of samples AZ.C11 and AZ.P3 can be explained by temperature discontinuities inside the oven. Some mineral transformations can be incomplete and only occur at the grain boundaries [21]. It is also possible that the quartz was formed during the cooling of the tiles [16].…”

“…During the firing of Ca-Mg-rich clays for ceramic production, the formation of a large number of mineral phases occurs [17]. In the formation of minerals, such as gehlenite, anorthite, wollastonite, found in the samples of Groups 1 and 2, the use of Ca-rich clays was verified, because these minerals originate from the reaction between silica and calcium compounds [14,21,25] 21,26] or, in the case of anorthite, it can be derived from reactions of gehlenite with aluminum phases (metakaolin) and silica [26]. Regarding the formation of diopside, found in Group 2 samples, it is probable that Ca-Mg-rich clays were used, because this mineral originates from the reaction of silica with phases of calcium and magnesium [25], possibly from mineral transformations of calcite and dolomite [16,27].…”