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(a) Record of temperatures in the first firing (kiln) and (b) second heating (cooking). (c) Record of temperatures of Experimental Vessel 10. See text for explanation.
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In this paper we report the results of an archaeomagnetic and rock-magnetic study performed on a set of Ne-olithic and Chalcolithic potsherds from El Portalón de Cueva Mayor site (Sierra de Atapuerca, Burgos, Spain) to investigate their thermal history and obtain information about their function during ancient times. Two types of palaeomagnetic beh...
Contexts in source publication
Context 1
... and subsequently further heating over a hearth). Four thermocouples were used in the first firing: two at the base of the kiln and two attached to the inner wall of some of the vessels, taking readings every 5 min for 260 min. From minute 30, the pots were placed on the ashes and fuel was added, coinciding with the highest temperatures recorded (Fig. 3a). One of the pots (No. 8) exploded due to thermal shock and was not ...
Context 2
... temperatures attained in the first firing in the kiln exceeded 600-700 °C (Fig. 3a), enough to record a full TRM. Subsequently, five out of the nine available vessels were selected for a second heating on a hearth (Samples 4, 5, 6, 7 and 10; Table 1). The purpose of this second heating (duration 140 min) was to reheat the vessels, simulating a cooking activity by placing them directly on the embers (Fig. 2c and d). ...
Context 3
... 1). The purpose of this second heating (duration 140 min) was to reheat the vessels, simulating a cooking activity by placing them directly on the embers (Fig. 2c and d). Two thermocouples were used: one located in the embers and another movable on the outer surface of the pots. Although the temperature recorded in the pots barely exceeded 200 °C (Fig. 3b), it is very likely that it has been underestimated, taken into consideration that the embers on which the recipients were deposited (what is really heated) recorded temperatures of around 400-450 °C (Fig. 3b). No anomalous (technical) reading of the thermocouples was observed and such temperature differences recorded between the embers ...
Context 4
... in the embers and another movable on the outer surface of the pots. Although the temperature recorded in the pots barely exceeded 200 °C (Fig. 3b), it is very likely that it has been underestimated, taken into consideration that the embers on which the recipients were deposited (what is really heated) recorded temperatures of around 400-450 °C (Fig. 3b). No anomalous (technical) reading of the thermocouples was observed and such temperature differences recorded between the embers and the outer surface of the pots is because the readings with the movable thermocouple were taken around 3-5 cm away from the embers. The pots were magnetically oriented in situ with a Brunton compass and ...
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... The use of thermal demagnetization for the reconstruction of firing temperatures was suggested by Goulpeau [28], who used it to distinguish between magnetic signals recorded when building materials were pre-fired and signals recorded when they were reheated to lower temperatures during the use of a Roman hypocaust. Similarly, Francés-Negro et al. [29] used this method for estimating firing temperatures in order to distinguish between storage vessels and cooking pots. In this paper we further develop and test this archaeomagnetic technique, suggest an interpretation method and demonstrate how it can serve as a useful complementary technique. ...
Burnt materials are very common in the archaeological record. Their identification and the reconstruction of their firing history are crucial for reliable archaeological interpretations. Commonly used methods are limited in their ability to identify and estimate heating temperatures below ~500⁰C and cannot reconstruct the orientation in which these materials were burnt. Stepwise thermal demagnetization is widely used in archaeomagnetism, but its use for identifying burnt materials and reconstructing paleotemperatures requires further experimental verification. Here we present an experimental test that has indicated that this method is useful for identifying the firing of mud bricks to 190⁰C or higher. Application of the method to oriented samples also enables reconstruction of the position in which they cooled down. Our algorithm for interpreting thermal demagnetization results was tested on 49 miniature sun-dried “mud bricks”, 46 of which were heated to a range of temperatures between 100⁰C to 700⁰C under a controlled magnetic field and three “bricks” which were not heated and used as a control group. The results enabled distinguishing between unheated material and material heated to at least 190⁰C and accurately recovering the minimum heating temperature of the latter. Fourier-Transform Infrared Spectroscopy (FTIR) on the same materials demonstrated how the two methods complement each other. We implemented the thermal demagnetization method on burnt materials from an Iron Age structure at Tell es-Safi/Gath (central Israel), which led to a revision of the previously published understanding of this archaeological context. We demonstrated that the conflagration occurred within the structure, and not only in its vicinity as previously suggested. We also showed that a previously published hypothesis that bricks were fired in a kiln prior to construction is very unlikely. Finally, we conclude that the destruction of the structure occurred in a single event and not in stages over several decades.
... Firing is an oxidizing process usually described by a set of variables, such as heating and cooling rates, soaking time, duration, firing atmosphere, thermal homogeneity (Livingstone Smith, 2001;Maggetti et al., 2011;Thér et al., 2019). Experimental archaeology shows that during two (or more) firing events quite different firing conditions may occur, even within the same combustion structure, especially when firing is in open-air (Livingstone Smith, 2001;Bentsen, 2013), while quite similar conditions may be observed within different structures even when they are of completely different type (Gosselain and Livingstone Smith, 1995). Thus, the reconstruction of any ancient firing process is a challenging task. ...
... Based on the strong dependence of clay magnetic properties on firing conditions, rock magnetism proved to be a powerful tool to investigate several archaeological questions related to firing. Studies in this direction include mechanisms of prehistoric settlement burning , thermal gradients within combustion structures (Spassov and Hus, 2006;Morales et al., 2011;Carrancho and Villalaín, 2011;Kondopoulou et al., 2014), technological characteristics of ceramics (Beatrice et al., 2008;Rasmussen et al., 2012;Karacic et al., 2016;Kostadinova-Avramova et al., 2018), and functionality of pottery (Francés-Negro et al., 2019) or other baked clay artifacts with unclear use (Tema et al., 2022). However, the possible relation between the combustion structures and the acquired magnetic properties is rather under-exploited, although such an application would definitely be of great archaeological interest (Herries et al., 2007;Eramo and Maggetti, 2013;Dimitrov and Kostadinova-Avramova, 2019). ...
... Empirical data show a wide range of firing temperatures (T firing ), from around 500 • C to over 900 • C (e.g., Livingstone Smith, 2001;Maggetti et al., 2011), rising faster in the places with most oxygenated fuel and decreasing rapidly with fuel combustion (Thér et al., 2019). Heating rate may vary from a few to over one hundred degrees per minute, and it is therefore considered as the most decisive firing parameter for distinguishing "open-air" from "kiln" firing (Gosselain and Livingstone Smith, 1995). Duration of the process and soaking time are relatively short when no fuel is added. ...
Rock magnetism has a significant potential to elucidate archaeological issues related to firing process owing to the strong dependence of clay magnetic properties on firing conditions. The present study is an attempt to characterize some basic fuel installations (hearths, household ovens, pottery kilns, kilns for building ceramics and metallurgical ovens) by the most common magnetic parameters (magnetic remanence, initial magnetic susceptibility, Koenigsberger ratio, frequency-dependent magnetic susceptibility and viscosity coefficient), accumulating a set of relevant magnetic data for exemplary structures. Rasmussen method was used for firing temperature determinations.
It is concluded that household ovens, used for cooking/heating activities only, were fired at temperatures below 500 °C. The acquired thermoremanence is in most cases partial TRM, generally less than 800 mA/m, the measured magnetic susceptibility does not exceed 300× 10−8m3/kg, and the corresponding Q ratios are mostly below 10. Experimentally baked clays show that already a firing at temperatures slightly above 500 °C yield much stronger and more stable TRM, and higher χ and Q ratio. Hearth and pottery kilns appear indistinguishable at this research stage, but systematically higher Q ratios were observed for the pottery kilns. Rising the temperature in the kilns for building ceramics and metallurgical ovens causes formation of a higher proportion of coarse-grained hematite and epsilon iron oxide, resulting in thermoremanence increase and magnetic susceptibility decrease.
Firing temperatures determined for the household ovens corroborate well the observed magnetic parameters indicating a maximum operating temperature of not more than 460–470 °C. On the other hand, they appear to be underestimated when the highest firing intensity was expected (at T > 900 °C). This is indicative that further studies in this aspect are needed. The slags studied fail to produce any feasible result in terms of their firing temperatures, probably because of their strong inhomogeneity and/or complicated firing history. There is an excellent agreement between the estimated temperatures for clays baked in an experimental dual chamber kiln and the thermocouple readings. Differences in firing atmosphere between archaeological structures (or their experimental analogues) and laboratory furnaces probably have the least effect on low-temperature heated objects (i.e., household ovens) and the strongest on high-temperature ones where reducing conditions dominate that should be taken into account in the data interpretation. An overestimation of Tfiring can happen for low-temperature materials due to possible intense magnetic transformations above 600 °C.
... Among them, archaeomagnetism is a very promising but still under-utilized technique. Even though during the last decades it has been increasingly used as a dating tool (Herries et al. 2008;Tema et al. 2013Batt et al. 2017;Casas and Tema 2019) or as ancient heating temperature indicator (Spassov and Hus 2006;Rasmussen et al. 2012;Kostadinova-Avramova et al. 2018;Jordanova et al. 2018;, its great potential on pottery use studies is still very little exploited (Francés-Negro et al. 2019). ...
Even though multidisciplinary approaches are widely used for the investigation of archaeological findings, magnetic analyses are still little exploited and only rarely applied to the determination of ancient artefacts use. Here, we present the results of a combined archaeological, morphological, and magnetic study carried out on the ring-shaped clay artefacts found in large quantities at the Iron Age site of Villa del Foro (Alessandria, Northern Italy). The shape and the significant number of such artefacts make their archaeometric investigation very interesting in order to understand the technological conditions of their production and use. A morphological investigation carried out on 640 fragments showed inhomogeneity in their dimensions, color, form, and clay refinement. Magnetic measurements show thermal stability after heat treatment up to around 500–600 °C, while further heating at higher temperature introduces some magnetic mineralogy changes. Thermal demagnetization of the samples generally shows a strong and stable thermal remanent magnetization. In few cases, a clear secondary component is present, suggesting partial re-heating or displacement at temperatures ranging from 200 to 450 °C. The results obtained indicate that the investigated ring-shaped artefacts were baked during their manufacture at temperatures of at least 600 °C. The archaeomagnetic investigation does not show any systematic evidence for magnetic components related to cooking activities and it is therefore suggested that the rings were used as weight looms and baked only during their production procedures. Such pilot study can be used as reference for the identification and study of similar objects found in other archaeological sites worldwide.
... All values but one are over unity indicating that the magnetization is most probably of thermal origin and are in the range of other burnt archaeological and experimental materials such as hearths, pottery or fireplaces (e.g. Francés-Negro et al., 2019;Herrejón Lagunilla et al., 2019;Kapper et al., 2014). ...
By studying combustion structures, which conceal information about anthropogenic activity, we might learn about their makers. This is especially important for remote time periods like the Middle Paleolithic, whose archaeological record comprises numerous combustion structures. The majority of these are simple, flat, open hearths, although a small number of features situated in pit-like depressions have been recorded. Given that hearths built on a flat surface can result in pit-like color alteration of the underlying sediment, accurate identification of pit hearths is a crucial step prior to behavioral interpretation. Here we present a comprehensive study of a possible pit hearth from the Middle Paleolithic site of El Salt, Spain, using a microcontextual approach combining micromorphology, lipid biomarker analysis, archaeomagnetism and zooarchaeology. This pit hearth involves a true depression containing a thick plant ash deposit. It reached very high temperatures, possibly multiple burning events and long combustion times. Morphologically distinct combustion structures in a single archaeological context may indicate different functions and thus a diverse fire technology, pointing to Nean-derthal behavioral variability.
Dating analysis of potsherds from three of the six units recently excavated in the Tingambato archaeological site, central-western Mexico, was carried out employing two regional intensity Paleosecular Variation Curves (PSVC) and the global model SHA.DIF.14k. A complete evaluation of the ceramic fragments' magnetic characteristics was done to determine the samples' magnetic carriers and their capacity to provide reliable archaeointensity data. The presence of two magnetization components in five analyzed potsherds provides two snapshots of the Earth's magnetic field intensity behavior at different temporalities. Intensity values were obtained following strict quality criteria, including cooling rate and anisotropy corrections. The principal causes of failure in archaeointensity experiments are associated with the alteration of the magnetic mineralogy during the heating of the specimens and with the presence of MD grains. Intensities within the established quality criteria were obtained for four out of the eleven ceramic fragments analyzed. The dating exercise shows a better correspondence of the intensity values with the regional curves than with the global model, especially for the temporal range between AD 400–1200, for which both regional curves are in good agreement. The obtained archaeomagnetic ages had a good correspondence with the radiocarbon ages reported in previous studies. By determining two archaeointensity values in one of the studied potsherds: one associated whit its fabrication and the other related to the fire (after which the site is supposed to be abandoned), archaeomagnetic ages of the probable end of Tingambato occupation were estimated.
The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material, or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20° C and > 600° C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 K and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540° C and 620° C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140° C and 240° C, and its magnetic properties correspond to an enigmatic High Coercivity, Stable, Low-unblocking Temperature (HCSLT) phase reported earlier. In a few samples high- and low unblocking temperature, magnetically hard phases appear to coexist, in the others the HCSLT phase is the only magnetically hard mineral present.
