Firing Techniques of the Impasti from the Protohistoric Site of Concordia Sagittaria (Venice)

⁵⁷Fe Mössbauer spectroscopy provided relevant information on the firing techniques employed in manufacturing concotto and coarse pottery, two types of fired clay mixtures (impasti) of the protohistoric settlement site of Concordia Sagittaria. The firing techniques of Concordia were reconstructed by comparing the Mössbauer patterns of the artefacts with those of the local raw clays fired in the laboratory. The concotto was produced in kilns by firing clay mixtures under oxidizing conditions at 700–1000°C, or at lower temperatures in the open air. The firing of these clay mixtures containing mainly ground pieces of waste pottery, resulted in hard and variously coloured construction materials, particularly suitable for humid environments. In turn, the coarse pottery was produced by firing clay mixtures more homogeneous than those used for the artefacts of concotto. The firing of coarse pottery was performed under reducing conditions at about 900°C with a final exposure to air by opening the hot kiln. Light and agreeable coarse pottery, with a red surface on the grey-black core, was obtained when the effective temperature of air was higher than 500°C.     

Firing temperature of a clay core sample in a bronze tripod from Daxinzhuang Site in China using TL techniques

In this paper, we studied the thermal history of a clay core sample from one leg of a bronze tripod unearthed at Daxinzhuang Site, Shandong, China. The properties of the luminescence signals of quartz depend on the maximum temperature at which the quartz was annealed in the past. We examined the feasibility of measuring the thermoluminescence (TL) sensitivity change of quartz for exploring the firing temperature of archaeological materials. The sensitization factor of the 110°C TL peak (S₂/S₁) and the ratio of the 210°C TL peak to the 110°C TL peak at different annealing temperatures were utilized to unveil the firing temperature in the clay core sample. The firing temperature of the clay core sample was approximately 700°C–800°C, proving the clay core has been fired. This result proved that the clay core has been fired by human agencies and indicated on the temperature of the clay core in drying and firing given by the foundry workers before the actual casting step.     

Ceramics Technology at Late Classic K’axob,Belize

Abstract

Excavation of a Late Classic Maya platform at K’axob, Belize, has revealed a suite of pit features and associated artifacts that are strongly suggestive of pottery production. Interpretation of the features as remnants of pit kilns used to fire pottery is bolstered by comparanda from the Andean region. Archaeometric and experimental replication studies also support the interpretation of this locale as one of pottery fabrication. Findings discussed include features identified as kilns, raw material suitable for temper, lumps of fired clay, ground stone, and expedient clay-working tools made of recycled pottery sherds. This research contributes to knowledge of the organization of Maya pottery production by providing the most comprehensive information presented to date on the technology of ancient Maya pottery fabrication and firing.     

THE DETERMINATION OF BRICK PROVENANCE AND TECHNOLOGY USING ANALYTICAL TECHNIQUES FROM THE PHYSICAL SCIENCES*†

This work applies established analytical techniques from the physical sciences to Irish brick, in order to gather evidence of ceramic technologies, provenance and sources of raw materials. Petrographic microscopy, X‐ray diffractometry and scanning electron microscopy with an energy‐dispersive X‐ray diffraction attachment were used to study the brick of Rathfarham Castle, Dublin, built c. 1618, where clay brick was introduced in 1771. Local clay was fired in the laboratory and analysed in a similar manner. The petrography of the pointing mortar was studied in order to gather evidence of ceramic provenance. This paper concludes that the brick was hand‐ moulded with a silica‐based, predominantly non‐calcareous clay of glacial origin, gathered locally, including fluxes and a high percentage of non‐plastic material. The mineralogy and petrography of the brick, together with the presence of pebbles and a coarse matrix, suggest that the raw clay was probably gathered from a glacial deposit. The presence of abundant pebbles and colour inhomogeneities suggests a lack of processing of the raw clay. The brick was probably fired in clamps at top firing temperatures ranging from 750°C to above 900°C. Transformation of limestone temper involving the breakdown of calcite and the generation of calcium silicates, and the new formation of plagioclase, high‐temperature quartz, hematite and spinel were revealed. The presence of spinel in ‘hot spots’ indicates that fuel was added to the raw clay in order to assist firing.     

Churchwarden Clay Tobacco-Pipes and the Southorn Pipemaking Family of Broseley,Shropshire

Abstract

The origin of the term ‘Churchwarden pipe’, now used to describe any long-stemmed clay—and sometimes even brier—pipe, is examined and the suggestion made that it was originally invented by the prominent Broseley, Shropshire, clay pipemaking family of Southorn to describe a specific type among their long-stemmed pipes. The Southorn family, whose products were possibly the premier-quality British clay pipes of the nineteenth and early twentieth century, is also discussed in the light of available evidence, much of which is confused or contradictory.     

ON THE USE OF COLOUR COORDINATES TO EVALUATE FIRING TEMPERATURES OF ANCIENT POTTERY*

Colour measurement was investigated as a means to evaluate equivalent firing temperatures of ancient pottery. Colour coordinates were determined on samples of six clays previously fired, and then refired, in the temperature range 600–1100°C. Under the adopted conditions, significant variations of colour hue and saturation were normally observed on refired samples only after the original firing temperature had been exceeded; less reliable information was provided by luminosity. Original firing temperatures of clay samples were correctly recognized in most cases by projecting the points representing samples’ colour on to the a*b* plane of the ClEL*a*b* colour space.     

Determining the Firing Temperature of Low‐Fired Ancient Pottery: An Example from the Donghulin Site,Beijing, China

The traditional thermal expansion method using a dilatometer fails to accurately determine the original firing temperatures of low‐fired ancient pottery. For this reason, we have developed an improved method of determining firing temperatures for low‐fired pottery. This paper explains the theory of the improved method and presents the reasonably satisfactory results obtained on ancient pottery from the Donghulin site (c. 10 000 bp ). The method and the results are very important for the study of ancient pottery culture and clay moulds used for bronze casting.     

Chemical characterization of clay pipes and wig curlers from Roy’s Orchard,Pipe Aston,Herefordshire

Abstract

Excavation on the site of a late 17th-century and early 18th-century clay tobacco pipe kiln and workshop at Roy’s Orchard, Pipe Aston, in north-east Herefordshire has revealed that the site was probably used concurrently by a number of pipemakers, from c. 1680 to c. 1720 or slightly later. In addition to marked and unmarked pipes, the waste from the site includes unmarked wig curlers of two types. Chemical analysis of a sample of pipes and wig curlers and of pipeclays which might have been the source of the clay reveals that the wig curlers are probably products of the Pipe Aston pipemakers and that they were made in two batches, corresponding to their typological classification. The source of the clay used has been shown conclusively not to have been the locally available Silurian clays but a Coal Measures seatearth, comparable with the outcropping at Ironbridge Gorge. Samples of Devon Ball clay and Coal Measures clay from Clun, a closer outcrop than Ironbridge, have been analysed and can be discounted as potential sources of the Pipe Aston pipeclay.     

MINERALOGICAL INVESTIGATIONS OF MEDIEVAL BRICK SAMPLES FROM BÉKÉS COUNTY (SE HUNGARY)

Brick samples from nine archaeological sites representing seven contemporary medieval settlements in Békés County (SE Hungary) were analysed by quantitative X‐ray powder diffraction, optical microscopic, scanning electron microscopic and coupled thermal analytical – evolved gas analytical methods. The aims of this study were to give a mineralogical–petrographical characterization of the brick samples, to gain possible information on the raw clay and the admixed materials, and to determine the firing techniques applied in medieval southeastern Hungary. The mineralogical composition of the samples suggests that the locally extracted clay was mixed with fluvial sand and wheat (Triticum monococcum L.) chaff. The moulded bricks were fired in clamps. The different degrees of calcite consumption suggest that the firing temperature ranged from ～750°C to ～950°C. Moreover, the well‐developed reaction coronas on calcite grains indicate long firing times, lasting perhaps several days.     

Lipid Residues from Low‐Fired Pottery

This paper assesses the fate of lipids associated with low‐temperature and pit‐fired pottery to determine to what degree organic compounds persist or are removed during short‐firing episodes below 800 °C. Three different types of clay were fired using contrasting techniques including at 400 °C for 4 h in a muffle furnace, and pit‐firing in which pottery was fired to higher temperatures but for shorter periods of time. Total lipid extracts obtained by solvent extraction of test sherds were screened using gas chromatography‐flame ionization detection (GC‐FID) to determine the lipid concentrations and gas chromatography–mass spectrometry (GC–MS) to identify the organic compounds present. The results showed that firing of clay removes all naturally occurring alkyl lipids; however, during pit‐firing, diterpenoid lipids were introduced into the clay as a condensate from pine ( Pinus spp.) wood used as fuel. These results confirm that alkyl lipids, e.g., fatty acids, can be reliably associated with the use of vessels, although caution is required when interpreting the origins of lipids that might derive from fuel used in firing.     

FOCUS: Provenance of Ceramics Revealed by Magnetic Susceptibility and Thermoluminescence

A new method for provenance determination of ceramics is presented. The samples were measured for magnetic susceptibility and for the TL intensity produced by artificially induced radiation in a pre-heated sample. Characteristic differences in magnetic susceptibility and TL sensitivity were found to exist between different clay sources, and in a diagram of susceptibility versus TL intensity, ceramics of different provenances often plot in distinctly different areas. Samples of 0·01–1 g of burnt clay were used. The method has been tested on a dozen archaeological sites, three of which are presented here as examples. Choice of tempering material, firing temperature, and oxygen tension during firing affect the susceptibility and the TL signals somewhat, and these effects have been tested experimentally.     

Pottery firing temperatures: a new method for determining the firing temperature of ceramics and burnt clay

A new method for determining the maximum firing temperature of ceramics and burnt clay is presented. The technique relies on measuring the magnetic susceptibility on a step-wise re-fired sample. The validity of the method has been tested by determining firing temperatures of two sets of clay samples fired at temperatures ranging from 400 to 1000 °C. Aliquots of the same samples have been studied petrographically by optical microscopy on thin sections and analyzed by powder X-ray diffraction in order to monitor structural and mineralogical changes as a function of temperature. The method is demonstrated on samples from four geographically widely different sites and it is applied to a larger set of ceramics of Late (ca. AD 900–AD 1450) and Inca (ca. AD 1480–AD 1532) periods from the Northwestern Argentine region, dating to a limited period of time prior to the fall of the Inca Empire. The method is shown to be a powerful tool in revealing archaeological information about the change in firing technologies in the pre-Hispanic societies in the Andean area through time.     

苏家村遗址烧土样品的过火温度研究

烧土制品作为最早的人工建筑材料,使人类的居住环境得到了根本性的改善。然而,学界关于烧土建筑的成因存在人为烘烤处理、缘自火焚、废弃习俗等多种观点。通过科技手段研究烧土制品的过火温度,有助于科学分析烧土建筑的成因,探讨与之相关的建筑工艺,丰富史前建筑史研究。磁学研究表明,考古遗址中的土壤及其他沉积物在受热后新生成了磁铁矿、磁赤铁矿等强磁性矿物导致磁性显著增强,且矿物成分和磁性几乎不会再发生变化;但当重烧的温度接近或大于原始烧成温度时,样品中原始矿物的破坏或新矿物的生成,会引起矿物磁性的改变。基于这一原理,实验室内分析受热黏土的磁化率随再加热温度的变化特征,可反映烧土制品的过火温度。苏家村遗址是大汶口文化晚期至龙山文化中期早段一处重要的聚落遗址,遗址中第5层为厚约20～40 cm的红烧土层且覆盖整个遗址,推测为房屋倒塌造成的建筑垃圾堆积层或人为堆积层,出土大量烧土块。本研究利用X射线衍射分析法、X射线荧光光谱分析法和磁化率法等对苏家村遗址出土的烧土样品开展了组成及构造特征和样品的过火温度的综合分析。结果表明,苏家村遗址烧土样品中的白灰层中人为地添加了白色陶土原料,土层中有意地添加了植物残骸作...     

ON THE INFLUENCE OF DRYING AND FIRING OF CLAY ON THE FORMATION OF TRACE ELEMENT CONCENTRATION PROFILES WITHIN POTTERY*

On experimentally fired briquettes made of five chemically and mineralogically different clays, trace element concentration profiles from the centre to the surface of the briquettes have been measured by Neutron Activation in order to examine if drying and firing of the clays lead to a mobilization and subsequent migration of single components within a sherd. Mineralogical changes during firing have been determined by X‐ray diffraction. Generally, no such migration could be found. For two clays, arsenic was lost from the briquette during firing, forming non‐constant concentration profiles. If NaCl is present in the clay paste, sodium migrates towards the surface. Additionally, in the special case in which the presence of NaCl coincides with that of calcite, the heavier alkali elements evaporate, forming significant concentration profiles within the sherd.     

The Coupled Influence of Relative Density,CSR, Plasticity and Content of Fines on Cyclic Liquefaction Resistance of Sands

In this study, stress-controlled cyclic simple shear tests were performed on sand specimens with up to 10% silt or clay contents, and coupled effects of plasticity, fines content (FC), relative density (D_R) and CSR (cyclic stress ratio) were investigated. The results demonstrated that for sands with low fines content, reasonable trends were obtained when the packing index control parameter was selected as D_R. Also, clean sand specimens demonstrated highest liquefaction strength compared with that of sands with fines up to 10% FC. The effect of fines’ plasticity became apparent as the FC increases and CSR reduces in relatively denser specimens.     

ARCHAEOMETRIC INVESTIGATIONS OF SGRAFFITO CERAMIC TILES (FIFTEENTH‐SIXTEENTH CENTURIES) RECOVERED FROM EXCAVATIONS IN UDINE (NORTH‐EAST ITALY)*

Most of the Renaissance sgraffito tiles excavated in Udine (Italy) constitute a homogeous group, the tile body having a CaO/MgO molar ratio ?= 3:2. They were produced using a dolomite‐ and calcite‐containing clay fired at 900–950°C. A small group of samples, with a lower firing temperature and a CaO/MgO ratio ?= 2:3, was probably produced in a different factory. Slip and transparent glaze, characterized by optical microscopy and inductively coupled plasma atomic emission spectrometry, are an illite‐rich clay and a lead silicate, respectively.     

The Potential of EBSD and EDS for Ceramics Investigations—Case Studies on Sherds of Pre‐Columbian Pottery

The work focuses on the potential of structural and chemical examinations by scanning electron microscopy based methods for archaeometric studies on ceramics. Achieved by a single preparation technique (polished block sections), the feasibility and benefits of electron backscatter diffraction are demonstrated as case studies using polychrome examples of pre‐Columbian pottery (Wari, Moche and Cajamarca). Elemental and phase maps allow for separate consideration of clay and temper. Identification of mineral phases and intergrowths of temper particles provide information for clarifying clay procurement and firing techniques with respect to local versus non‐local pottery to enlighten trade relations, technological transfer and shared heritage of pre‐Columbian cultures.     

Archaeometric Investigation of Medieval Pottery from Excavations at Novo Brdo,Serbia

Medieval pottery from excavations at Novo Brdo, Serbia, an important mining and trading centre during the 14th and 15th centuries, was investigated by a combination of optical microscopy, inductively coupled plasma – optical emission spectrometry, Fourier transform infrared, micro‐Raman and energy‐dispersive X‐ray fluorescence spectroscopy and X‐ray powder diffraction methods in order to determine its composition and firing temperature. The samples investigated were made of medium‐ to coarse‐grained, non‐calcareous clay, by a relatively well‐controlled firing procedure in an oxidizing atmosphere. The firing temperature was estimated to be 850–950°C. The similarity between the chemical composition of the investigated pottery and the local raw clay, combined with the outward appearance and the archaeological findings, indicate domestic production. The pottery is covered with the transparent lead‐rich glaze. Iron and copper were used as colourants.     

MODELLING CHANGES IN MOLLUSC SHELL INTERNAL MICROSTRUCTURE DURING FIRING: IMPLICATIONS FOR TEMPERATURE ESTIMATION IN SHELL‐BEARING POTTERY*

Firing experiments have been carried out on a clay containing naturally occurring fragments of mollusc shell. The transformation and/or decomposition of mineral phases with temperature was monitored by thermal analysis on the starting material and compared with X‐ray diffraction data on the fired specimens. Scanning electron microscopy revealed systematic changes in the internal microstructure of the shell fragments. Micrometer‐sized intra‐ and inter‐layer pores formed in the shells before the complete decomposition of calcite. The shape, dimension and location of the pores within the shell microstructure were found to be directly related to the firing temperature. The analysis of these microstructural features in archaeometric studies offers a good constraint on the estimation of the firing temperature in shell‐bearing pottery.     

Archaeometric analysis of ceramic production in Tiwanaku state (c.500–1000 ce): An exploratory study

The chemical and mineralogical characterization of seven ceramic fragments produced within Tiwanaku state (c.500–1000 ce ) is reported. The instrumental techniques used included X‐ray elemental and mineralogical chemical analysis, Raman spectroscopy, and scanning and light microscopy. The results indicate there are several clay types, although they show similarities, such as the use of a plant‐based temper. The red colour of the decoration is hematite, and manganese oxides such as jacobsite are present in the black. The white colour is a mixture of gypsum and clay, and the orange is a mixture of hematite and clay. The use of colours, the quality of the clays and the temperatures reached during pottery firing point to expertise in ceramic production and to complex decision‐making processes. The multi‐elemental archaeometric approach documented here could become an important tool to shed a light on ancient ceramic technology and the internal variance of Tiwanaku pottery.