COMMENT: CHEMICAL AND MINERALOGICAL APPROACHES TO CERAMIC PROVENANCE DETERMINATION

This comment concerns an ‘absolutist’ perspective on the superiority of mineralogical analysis over chemical analysis for the determination of ceramic provenance. This point of view has appeared in the literature in recent years, but it has not been justified and is not justifiable. Mineralogy and chemistry are complementary. They measure different things and are best used in combination to generate secure, geographically specific ceramic source assignments.     

DIATOMS AND CERAMIC PROVENANCE: A CAUTIONARY TALE*

In order to answer the age‐old question of whether a given pot was manufactured locally or elsewhere, some archaeologists have turned to geoarchaeological or bioarchaeological methods such as diatom analysis to establish potential clay sources. In this paper, we highlight the complexity of diatom analysis and illustrate how diatoms potentially coming from several sources may be introduced at different stages during the ceramic manufacturing process. Finally, we proceed to evaluate the reliability of diatom analysis as an archaeometric measurement for ceramic provenance, concluding that it may have a more limited usefulness within archaeology than its current frequency of use would indicate.     

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.     

PETROGRAPHIC AND GEOCHEMICAL EVIDENCE FOR LONG‐STANDING SUPPLY OF RAW MATERIALS IN NEOLITHIC POTTERY (MENDANDIA SITE,SPAIN)

Pottery from the Neolithic Mendandia site has been studied. The radiocarbon dating of the site corresponds to a range of dates from 7488–7546 cal bc to 5283–5437 cal bc : the first occurrence of pottery is dated at 5968–6040 cal bc for the lower level III, and up to 5386–5560 cal bc for level II. The antiquity of the potsherds places them within the oldest pottery production sequences in the Iberian Peninsula, which adds to the interest of this study. Ten potsherds from level II and five from level III are analysed for their petrographic and chemical characterization. The petrographic data show two different methods of raw materials manufacture—intentionally tempered pottery (ITP), using calcite and/or limestone and grog, and naturally or non‐intentionally tempered pottery (NTP). According to the matrix paste features, on the basis of the amount, shape, and average or size range of the mineral inclusions, clayed (type A) and sandy (type B) paste types were established and related to two different source areas. The chemical features also indicate two raw material sources and are in agreement with the petrographic paste types. The absence of significant chemical and mineralogical differences between the pottery from levels II and III suggests two contrasting areas for raw materials supply that lasted for at least 600 years.     

PROVENANCE OF MARBLES FROM NAXOS BASED ON MICROSTRUCTURAL AND GEOCHEMICAL CHARACTERIZATION

A detailed quantitative microstructural study coupled with cathodoluminescence and geochemical analyses on marbles from Naxos demonstrates that the analysis of microstructures is the most sensitive method to define the origin of marbles within, and between, different regions. Microstructure examination can only be used as an accurate provenance tool if a correction for the second‐phase content is considered. If second phases are not considered, a large spread of different microstructures occurs within sample sites, making a separation between neighbouring outcrops difficult or impossible. Moreover, this study shows that the origin of a marble is defined more precisely if the microstructural observations are coupled with cathodoluminescence data.     

THE SECTILIA PANELS OF FARAGOLA (ASCOLI SATRIANO,SOUTHERN ITALY): A MULTI‐ANALYTICAL STUDY OF THE GREEN,MARBLED (GREEN AND YELLOW), BLUE AND BLACKISH GLASS SLABS

Analyses at the Cu–K, Fe–K and Mn–K edge were performed to study the green, marbled (green and yellow), blue and blackish (deep greyish olive green) glass slabs decorating three sectilia panels from the archaeological site of Faragola. Results indicate that all slabs were made by mixing siliceous sand with natron, sometimes probably mixed with small percentages of plant ash. Cu²⁺ and Pb antimonates should be responsible for the opaque green colours. The dark green and yellow portions of the marbled slabs are respectively comparable to the slabs comprising only one of these colours. Cu²⁺ together with Ca antimonates probably produced light blue slabs, whereas cobalt was used to produce dark blue slabs. We consider it possible that the abundance ratio of Fe²⁺/Fe³⁺ and the complex Fe³⁺S^2? would have an effect on the blackish slabs. The contribution of Mn cannot be ascertained even if it could have played a role in darkening glass colour. The comparison between the chemical composition of Faragola samples and several glass reference groups provided no conclusive evidence of provenance; whereas, the presence of a secondary local workshop can be hypothesized.     

CHEMICAL COMPARISON OF RARE CHINESE WHITE POTTERY FROM FOUR SITES OF THE ERLITOU STATE: RESULTS AND ARCHAEOMETRICAL IMPLICATIONS

White pottery is among the most significant finds from China's earliest state, Erlitou (c. 1900–1500 bc ). Samples were primarily discovered in small numbers from elite tombs of a few sites, leading to the hypothesis that they were made at only a few locations and then circulated regionally as prestige items. To facilitate determining provenances, we compare the ICP–MS trace elements and TIMS Sr isotopes of whiteware with two soil samples from Nanwa, a possible manufacturing site, and with shards found at three other sites: Erlitou, Huizui and Nanzhai. The Nanwa shards demonstrate special elemental and Sr isotopic features. Considering the chemical observation and archaeological background together, we propose that Nanwa was a centre for whiteware production, although the two soil samples we collected there were probably not the exact materials used. Some whiteware pieces from Erlitou, Huizui and Nanzhai fall in the chemical field defined by Nanwa samples, indicating that they were possibly made at Nanwa. Many other samples from these three sites plot outside the Nanwa field, implying they were probably not Nanwa products. This study demonstrates that while chemical sourcing is very useful, firm archaeological context must remain the cornerstone of such research.     

AN ELEMENTAL AND LEAD‐ISOTOPIC STUDY ON BRONZE HELMETS FROM ROYAL TOMB NO. 1004 IN YIN RUINS

Lead isotope and element composition analyses were performed by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma optical emission spectroscopy (ICP–OES) on bronze helmets from royal tomb No. 1004 at Yin Ruins, the last capital of China's Shang Dynasty (17th to 11th centuries bc ). The data show that the copper‐based alloy helmets can be divided into two categories: tin bronze and leaded tin bronze; and the lead isotope ratios for both categories are in the range of highly radiogenic lead (HRL). This result offers some important clues to answering questions concerning the provenance of raw metal materials, as well as the chronology of this famous royal tomb.     

IDENTIFICATION OF AN ADHESIVE USED TO REPAIR A ROMAN JAR

A combination of micro-analytical techniques, including thin layer chromatography (TLC), gas chromatography (GC), and combined gas chromatography/mass spectrometry (GC/MS), was employed to study the lipid composition of an adhesive used to repair an Ecton ware jar, recovered from Roman sediments of the River Nene at West Cotton (Rounds, Northamptonshire, U.K.). GC of the total lipid extract of the adhesive showed a complex pattern which was difficult to interpret. TLC was used to fractionate the extract. The fractions were then trimethylsilylated and submitted to GC and GC/MS. Betulin, lupeol, lupenone, allobetul-2-ene, and several other pentacyclic triterpenoid compounds were shown to be present in the ancient material. The similarities between the lipid compositions of the adhesive and of contemporary birch bark tar and a birch bark total lipid extract led to the conclusion that the adhesive was derived largely from birch bark, thus providing the first firm evidence for the use of birch bark tar in ancient Britain.     

SCIENTIFIC ANALYSIS OF ROMAN GLASS FROM AUGUSTA PRAETORIA

Fifty-five fragments of Roman glass from Augusta Praetoria (Aosta, Italy) were analysed by inductively coupled plasma optical emission spectroscopy determining 15 elements (Si, Na, Ca, Al, Fe, Mg, Mn, Ti, Sr, Ba, Cr, Ni, Cu, Co and Pb) on dissolved samples; in addition, potassium was determined by flame atomic absorption spectroscopy. The analytical results indicate that all the fragments, with one exception, are silica-soda-lime glasses; (he exception is a potash glass. Cluster analysis was performed on the analytical data by accounting for either 14 (all the elements searched for but Ni and Pb) or eight elements (after further removal of Si, Fe, Mn, Cr, Cu and Co from the data set). The results obtained indicate that, once colouring and decolouring agents are removed, the classification of the glasses seems to be mainly determined by chronology; separate groups within coeval fragments may indicate different provenances.