Experimentally produced glass compared with that occurring at The Torr, NW Scotland, UK: vitrification through biotite melting

It is proposed that the vitrification in some Iron Age forts in NW Scotland can be explained through decomposition of micas (largely biotite) giving melts that react with or dissolve quartz and crystallise orthopyroxene and feldspars, so equating with the reaction biotite + quartz = sanidine + orthopyroxene + liquid. A sample of Moine semi-pelite has been experimentally melted at c. 850 °C demonstrating this breakdown reaction. A preserved thermal gradient across the sample reveals the progressive degradation of biotite towards the melting (upper) surface. Degradation is evident from the initial emphasis of mica cleavages in grains at the bottom of the sample, and then appearance and progressive increase in size of bubbles associated with biotite and melt towards the top of the sample. A chocolate-brown melt was produced as a coating on the upper surface and along micaceous layers. A near equivalent sample was located from the fort at The Torr that, whilst being more thoroughly affected by heat, with no unaffected biotite, preserved similar textures. Compositions of original Moine minerals are used to constrain the melts produced and melt evolution is tracked through quenched crystals. These include ternary feldspars as well as sanidine, spinels and orthopyroxene. Spot geochemical evidence demonstrates the heterogeneity of the melts, plus varying contributions of Ca and Na that could be attributed to the onset of reactions involving feldspars and other minerals from the original assemblage. It is thus concluded that a similar temperature to that of c. 850 °C derived in the experiment was reached in the vitrification process at The Torr in order to produce the glass observed.     

Is vitrification in charcoal a result of high temperature burning of wood?

The term ‘vitrified’ is used to describe the glassy appearance of some charcoals recovered in the archaeological record. It has been generally considered that this phenomenon is a result of wood being subjected to high temperatures similar to the role of temperature in the formation of glass and pottery. Charcoals displaying characteristics of vitrification from three distinct archaeological contexts were analysed using reflectance microscopy to determine their temperature of formation. Charcoal was also generated in laboratory charring experiments at temperatures of 900–1100 °C for durations of 1, 6, 12 and 24 h to determine if subjection to high temperature led to vitrification. None of the laboratory-produced charcoals displayed characteristics of vitrification. Mean random reflectance of the vitrified archaeological fragments indicated temperature of formation from 310 to 530 °C. A charring experiment was also conducted, at 500 °C for 6 h, using green wood with some bark attached, and added sugars, but no evidence of vitrification was seen. Therefore vitrified charcoals do not result from high temperature charring or primarily from the use of green wood.     

Magnetic detection of ship ballast deposits and anchorage sites in King Herod's Roman harbour,Caesarea Maritima,Israel

Ballast stone deposits are a common feature of sediments in ancient harbour basins but are often overlooked as a potential source of archaeological information. Recent geophysical investigations at Caesarea Maritima in Israel have discovered a thick, laterally extensive ballast layer in the area seaward of the 1st c. BC Roman harbour. The ballast deposits were identified by low-relief mounds on the seabed with elevated magnetic intensities. Jet probing and excavation of magnetic anomalies at several locations revealed a 20–60 cm thick rubble layer containing large quantities of Late Roman and Byzantine pottery, local sedimentary boulders (kurkar sandstone, limestone cobbles) and foreign igneous and metamorphic boulders (granite, schist, volcanics; ca. 50%). The foreign boulders and pottery identify the rubble layer as ballast and ships refuse jettisoned by merchant ships outside the harbour. The strong magnetic contrast between the ballast deposits and the natural seabed sediments is attributed to the high magnetic susceptibility (>10⁻³ SI) of crystalline boulders and pottery materials within the ballast rubble.     

Tracing firing technology through clay properties in Cuzco,Peru

The purpose of this study was to identify changes in firing practices that occurred during a timeframe that saw the introduction of European kiln technology to the Andes (AD 900–1800). Pottery from an excavated context at the archaeological site of Aqnapampa in the southern highlands of Peru was examined for changes in paste recipes that adapted local materials to increased firing temperatures indicative of evolving firing technologies. Sherds (60) and fragments refired to 890 °C from 12 stratigraphic levels were compared by style, surface treatment, paste color, and vitrification structures (ESEM). Four technological phases of the Cuzco pottery sequence emerged and were used to evaluate the trajectory of a single decorative style (Killke). Previously thought to have been produced in pre-Inca times and curated into later periods, the Killke sherds presented evidence that the style was produced using technologies introduced in the Inca and Spanish Colonial Period.     

Too little,too late: the geochemistry of a 1773 Philadelphia porcelain openwork basket

A dated (1773) openwork basket labelled “PHILADELFIA” attributed to the Bonnin and Morris factory has a lead-bearing, silicious–aluminous–calcic (S-A-C) composition that contrasts with the phosphatic (bone ash) porcelains known to have previously been made during the mid-1760s to early 1770s in what is now the United States. The basket was underfired and so contains relics of a flint (Pb) glass flux, but kiln temperatures were nonetheless sufficient for subsolidus pseudowollastonite and anorthite to have been resorbed, implying that the duration of firing (soaking) near peak kiln temperatures was insufficient to ensure thorough vitrification. During cooling, liquidus pseudowollastonite and silica polymorphs (but not anorthite) formed, showing that the melt was confined to the tridymite–pseudowollastonite cotectic above the Trd–Wol–An eutectic (1170 °C) in the SiO₂–Al₂O₃–CaO system. Rapid cooling is also indicated by quenched silica polymorphs in the relict glass particles. Although Bonnin and Morris employed some former Bow (London, c. 1743–74) workers, the S-A-C wares initially produced by this factory are compositionally distinct from the 1773 basket, which in this regard more closely resembles the body and glaze of a reputed Chelsea triangle-period (London, c. 1745–49) vessel. Regardless of how they obtained this technology, it is ironic that Bonnin and Morris chose to abandon phosphatic pastes in favour of what in Britain had become an obsolete formula.     

Roman blue-green bottle glass: chemical–optical analysis and high temperature viscosity modelling

Chemical analysis, optical absorption spectroscopy and mathematical modelling of high temperature viscosity have been carried out on five 1st–2nd century AD Roman blue-green bottle glass fragments from Coppergate, York. Modelled viscosities indicate remarkable consistency within the sample set studied and support the suggestion that temperatures of ∼1000–1150 °C were required to remelt these glasses and to provide suitable viscosities for forming articles. Iron redox ratios (Fe²⁺/ΣFe), analysed SO₃ contents and the absence of characteristic Fe³⁺–S²⁻ amber absorption bands suggest that melting conditions for all studied glasses were mildly, rather than strongly, reducing (estimated pO₂ ≈ 10⁻¹–10⁻⁶ bar). These furnace conditions are consistent with the effects of combustion gases and carbonaceous matter contained in the raw materials.     

A study by thermal treatment and X-ray powder diffraction on burnt fragmented bones from tombs II,IV and IX belonging to the hypogeic necropolis of “Sa Figu” near Ittiri,Sassari (Sardinia,Italy)

In the course of an anthropological investigation of three tombs of the hypogeic necropolis of “Sa Figu” (near the village of Ittiri in North Sardinia, Italy), numerous burnt bone fragments were collected. In particular, from the whole necropolis we selected a tenth of long bones from tomb IV, a small fragment of femur from tomb II and four fragments belonging to tomb IX. The aim of this work is to determine a temperature range to which the bone fragments were heated, in order to assess a funerary cremation which was presumably used at that time to quickly and hygienically eliminate the flashy parts of deceased people rather than a purification rite with fires inside the sepulchres. We attempted to evaluate the range of temperature to which the bones were likely subjected, making a joint use of thermal treatment and powder X-ray diffraction investigations. From our X-ray line broadening results carried out with a modern approach (Rietveld method), it emerged that a group of five fragmented burnt bones (one specimen belonging to tomb IV, the other four from tomb IX) were subjected to a heat treatment in a temperature range from 600 and 750 °C. Conversely another group of bones (belonging to tombs II and IV) turned out to be subjected to temperatures not higher than 250 °C.     

On the provenance and manufacture of red-slipped fine ware from ancient Cassope (NW Greece): evidence by X-ray analytical methods

Energy-dispersive X-ray fluorescence spectroscopy was used to characterize red-slipped pottery (2nd–1st century BC) from ancient Cassope, north-western Greece. The compositional data were statistically treated by principal component analysis and chemical groups were established, representing locally produced and imported items. Mineralogical investigation by X-ray diffraction indicated firing temperatures in the range from 850 to 1000 °C for most of the sherds, while one group consisted of over-fired items, possibly in excess of 1050 °C. The morphology and elemental composition of the ceramic bodies and surface slips were examined through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The analyses revealed that different pottery groups exhibit surface slips of different nature, in terms of thickness, degree of vitrification and elemental composition. Overall, the diversity in technological characteristics of the examined sherds is indicative of the socio-economic conditions prevailing in Cassopaea during the late Hellenistic period.     

Celtic vitrified forts: Implications of a chemical-petrological study of glasses and source rocks

The term “vitrified forts” refers to remnants of stony fortifications of early Iron Age in which constituent rock fragments and boulders have been melted and/or welded together by heat, apparently in situ. The methods used are a matter of controversy, and even the question whether the firing was constructive or destructive is disputed. In this study we present bulk analyses of some twenty source rocks and of fifty glasses (in petrographic thin sections) from eleven sites and attempt to relate these data to the processes (and purposes) producing the observed sintering, welding and melting. The results are consistent with progressive partial, sometimes total, melting of the rocks used. In agreement with most previous investigators we conclude that no exotic rocks (although limited amounts of clays or organic debris cannot be excluded) were used as flux nor were easily fusible materials selected. On the other hand, simply burning an ordinary (of the later murus gallicus type) timber-laced wall cannot account for the evidence of strongly reducing conditions and sustained high temperatures, probably for days and in some cases well above 1000 °C. Rather, the fires seem to have been contained, perhaps by filling the space between the rocks in the timber framework with soil, clay and combustible materials, e.g. peat, brushwood and domestic debris. We cannot conclude whether the firing was accidental, or set by enemies or by the builders. In any case, the builders appear to have used more sophisticated techniques than previously believed to ensure the durability of their constructions.     

A pilot study into the effects of X-ray and computed tomography exposure on the amplification of DNA from bone

This research investigates the intersection of radiography and aDNA, two commonly used methods in bioarchaeology. The goal of this project was to investigate the effects of radiation on the ability to amplify DNA from bone. Bones (n = 124) from domestic pig (Sus scrofa) feet were randomly sorted into a control group and four treatment groups: (1) single exposure X-ray; (2) single exposure CT; (3) multiple exposures X-ray; and (4) multiple exposures CT. Number of PCR cycles required to amplify DNA in 100 bp, 200 bp and 400 bp segments were used as a proxy for the amount of available DNA. In the 200 bp CT sample, distal phalanges required significantly more amplification cycles than did the other bones and were removed from analysis. Results suggest that in general radiation exposure fragments DNA thereby decreasing the amount that is amplifiable. While these results are suggestive, further research is required to elucidate the degree to which radiation fragments DNA in archaeological specimens.     

The geochronological potential of isoleucine epimerisation in cassowary and megapode eggshells from archaeological sites

Our research demonstrates that the extent of isoleucine epimerisation (A/I) in fragments of avian eggshells provides geochronological information in archaeological contexts. In the archaeological sequence of Hay Cave, northern Queensland, Australia, there is an excellent correspondence between the A/I values of Australian brush-turkey (Alectura lathami) eggshells (n = 99) and independent geochronological control (n = 16 radiocarbon ages including 4 on eggshell calcite). The A/I values identify three phases of deposition during the Holocene at Hay Cave. In contrast to the Alectura eggshell A/I values, a poor correspondence was observed between the A/I values of cassowary (Casuarius) eggshells from Toé (n = 35) and Kria caves (n = 23) (Ayamaru Plateau, Papua) and the depths from which the specimens were recovered in these stratified sequences. Given coherent archaeofauna trends and radiocarbon chronologies (n = 8 and 2 eggshell calcite radiocarbon ages at Toé and Kria, respectively) with respect to depth, the variable A/I values are not explicable in terms of mixing. Rather, the variability is most likely due to exposure of the eggshells to the high temperatures of campfires. Despite the variability, eggshells with relatively low A/I values amongst specimens recovered from similar depths (and therefore presumably least influenced by high temperatures) exhibit a gradual increase in A/I with respect to depth, as expected in a stratified deposit. From this observation it is suggested that the identification of heated eggshells will increase confidence in geochronological information provided by A/I. These studies illustrate the complications that arise from campfire-induced acceleration of amino acid racemisation and emphasise that although this phenomenon is common, it is not universally encountered in archaeological contexts.     

Morphological,chemical and physical changes during charcoalification of wood and its relevance to archaeological contexts

Wood exposed to a heat source can be transformed into charcoal if subject to conditions of carbonisation (in the absence of air) or charring (in restricted air). Charcoal recovered from archaeological sites can yield fundamental information to our understanding of human economic and cultural development over time and (ecological) setting. This work describes the morphological (anatomy, degree of shrinkage), physical (reflectance) and chemical (elemental, molecular composition) properties of charcoal in relation to heat source and wood variables. In this study charcoal and charcoal fuel were experimentally produced whereby temperature (160–1200 °C), time of exposure (2–1440 min), heating rate (high and low) and wood type (angiosperm and conifer) were varied. The results show that charcoal, often described as an inert, black material, has different chemical and physical properties in relation to the investigated variables. By using these different properties it is possible to distinguish between the different types of fires (domestic and industrial) exploited by humans in the past. Morphological analyses and reflectance measurements are effective tools for this purpose and can be used in wood exposed to temperatures of 300 °C and above—temperatures which are relevant to archaeological research. Angiosperm and conifer wood react in different ways when exposed to heat and thus the taxonomic identity of archaeological material needs to be known. Chemical analyses can be used for wood exposed to temperatures below 400 °C whereas elemental analyses of the carbon content can be used for wood exposed to temperatures up to a maximum of 650 °C.     

Going underground: experimental carbonization of fruiting structures under hearths

We show that carbonized fruits and seeds recovered from Middle Stone Age deposits in rock shelters are likely to have been carbonized as part of post-depositional processes. We buried indigenous South African fruits, nuts and seeds at pre-determined depths and distances from the centers of experimental fires. The cold ashes of the hearths and the sand surrounding them were subsequently excavated, using standard archaeological techniques and dry-screening. The fruiting structures from the oxidizing part of the fire were burnt to ashes, whereas those buried in sand under anoxic conditions survived in varying forms. Those buried 5 cm below the center of the fire were carbonized; those buried 10 cm below the center of the fire were dehydrated; and those 5 cm and 10 cm below the surface at the outer edge of the fire were unaffected. Size, moisture or oil content of the original fruit or seed did not appear to influence whether or not carbonization took place. Temperatures recorded 5 cm below the experimental fires suggest that the carbonization occurred at or before a maximum temperature of 328 °C, and also at lower maximum temperatures (152 °C) that were maintained for long periods. Even when the quantities of a particular wood are controlled, open fires may produce variable underground temperatures and the temperatures below ancient hearths would have been equally variable. We suggest that Cyperaceae (sedge) nutlets, the most numerous fruiting structures in the Sibudu Middle Stone Age archaeobotanical assemblage, occur in the shelter as a result of human activity, subsequent burial, and accidental carbonization when hearths were built directly above the buried nutlets.     

The Altars of Zeus and Hera on Mt. Arachnaion in the Argeia,Greece

Abstract

Pausanias (ii.25.10), who traveled extensively in Greece in the 2nd century A.C., mentioned the existence of two altars of Zeus and Hera on Mount Arachnaion above the village of Lessa in the Argeia of the Greek Peloponessos. Two travellers in the early 19th century climbed to the saddle between the two peaks of the mountain and saw there a quadrangular enclosure wall of polygonal masonry on a low hill which they assumed to be the site of these altars. Since then this identification has been accepted by most scholars, including J. G. Frazer. Since most altars of Zeus are found on or near the top of the mountains, I climbed the mountain to check this attribution.

A section of a crude polygonal retaining wall exists on the hill but no traces of the altars were found. Obsidian bladelets and sherds found on the surface suggest that the wall might mark the location of a farmstead or small settlement dating as early as the Bronze Age. On the summit of the western peak of the mountain two low foundations of rubble masonry and three concentrations of sherds and burnt animal bone fragments in a blackish-brown soil matrix were discovered. One of the foundations must represent the ruins of the chapel of Hagios Elias known once to have stood on the summit. The sherd concentrations, which date from the mid-8th century B.C. through at least the 6th century B.C., must represent remains associated with the altars of Zeus and Hera.     

Lower Pecos and Coahuila peyote: new radiocarbon dates

Peyote, a psychoactive cactus native to the Chihuahuan Desert, has been preserved from excavations at only two archaeological sites: Shumla Caves in the Lower Pecos region of southwest Texas and shelter CM-79 near Cuatro Ciénegas in Coahuila, Mexico. We determined three indistinguishable radiocarbon ages of 5160 ± 45, 5200 ± 35, and 5210 ± 35 ¹⁴C years BP, yielding a mean age of 5195 ± 20 ¹⁴C years BP for the three specimens from Shumla Caves. For one of the Cuatro Ciénegas specimens we obtained the first direct radiocarbon date of 835 ± 35 ¹⁴C years BP. This study demonstrates the use of peyote by inhabitants of the Lower Pecos region of the Chihuahuan Desert about 6000 calendar years ago, and confirms its use by inhabitants of the Cuatro Ciénegas region of the Chihuahuan Desert in Late Prehistoric times. The Shumla Caves' specimens are composed of an aggregate of ground peyote mixed with other plant material, i.e., they appear to be manufactured peyote effigies, and are definitely not intact peyote buttons.     

Identification of fragmentary bone from the Pacific

We explore bone microstructure for taxonomic identification of archaeological bones too fragmentary to permit secure identification on morphological grounds. Backscattered electron (BSE) imaging is used to observe bone tissue types and the arrangement of vascular canals, and to facilitate quantification of osteonal canal dimensions. Examination of known examples of relevant taxa (humans [n = 8], pigs [n = 4] and dogs [n = 4]) shows significant differences among them. When the results of this examination are applied to a blind test of modern and archaeological specimens (humans [n = 8], pigs [n = 2]), 100% of specimens are identified correctly. The approach is applied to 13 morphologically unidentifiable fragments from Hawai’i and Fiji to evaluate its potential for identifying bone tools and to increase the number of samples available for dietary analysis. Potential applications of the approach for other contexts are discussed.     

Fire and ritual: bark hearths in South-American Tupiguarani mortuary rites

High proportions of bark pieces (up to 85% of the charcoal content) were found in several hearths from Morro Grande archaeological site (Southeastern Brazil). This site, dated between 3220–2840 and 1820–1390 yrs cal BP, is associated to the Tupiguarani Tradition, attributed to supposed ancestors of Tupinambá native populations, who occupied the major part of the Brazilian coast in the XVIth century. Bark hearths, archaeologically associated with the mortuary ritual, were found encircling a funerary urn and associated with ceramic fragments painted with elaborated patterns in black, white, and red. Other hearths, spatially isolated from the funerary area, were associated to fragments of utilitarian non-painted ceramics and therefore attributed to domestic contexts. These ones presented few or no bark fragments. It is clear that bark was intentionally selected as fuel for the funerary hearths. Although bark is related, in historic accounts, as a specialized firewood for ceramics firing, its presence in ritual context has not been previously recorded. In this paper, the anthracological record is discussed in the light of ethnographic and historic accounts. A possible explanation for the presence of bark hearths in funerary context is proposed, suggesting it might be a symbolic parallel with the quotidian: the potency and power of transformation of bark as a fuel would be regarded in a spiritual level, achieving the transformation of the body soul in the revered soul – an Ancestor.     

Identifying a Roman Casting Pit at Tel Dor,Israel: Integrating Field and Laboratory Research

Abstract

The functional identification of industrial features is difficult when few characteristic artifacts are preserved. We studied a Roman-period pyrotechnological feature at Tel Dor, Israel, where the only possibly diagnostic ceramic artifacts were found in fill between the walls and above the floor, rendering their association with the feature itself uncertain. The ceramic artifacts included coarse slabs and fragments of utilitarian vessels, some vitrified with adhering bronze droplets or slag-like residues. Analysis of the sediments within and around the industrial feature, using an X-ray fluorescence spectrometer on-site, revealed high concentrations of copper and lead, indicating metallurgical activity. Lead isotope analyses showed that the slag-like residue adhering to a ceramic fragment had the same isotopic values as the sediments, implying that the fragment was associated with the activities carried out in the feature. Microscopic and chemical analyses of the slag-like residue demonstrated that it was produced from melting leaded bronze. Some of the ceramic fragments contained elongated impressions on their inner surfaces, similar to those of casting molds found at other sites. We propose that the feature was used as a casting pit for bronze objects.     

Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment

The early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations. Lithic vestiges are the only sources that remain of this process and the understanding of the material’s properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment. Several models of the structural transformations upon heating have been proposed in the current literature. These models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony. In order to propose a new model, we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy, solid state NMR, X-ray diffraction and electron microscopy. The results show that the major transformation to happen is the loss of silanole (SiOH) and the creation of new Si-O-Si bonds according to the reaction: Si?OH HO-Si → Si-O-Si + H₂O. This reaction starts between 200 °C and 300 °C and causes an increase in the hardness of the rocks. The maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created H₂O and depend on the size of the specimen and the volume of its porosity. These results also show that the annealing duration at maximum temperature can be relatively short (<50 min) for a sufficiently large amount of transformation to be accomplished.     

Pre-pottery farmers on the Pacific coast of southern Mexico

Large island-like shell mounds along the southern coast of Mexico are the earliest known archaeological sites on the Pacific margin of Mesoamerica. These aceramic deposits date to between 7500 and 3800 cal BP and have been interpreted as locations where foragers, living elsewhere seasonally on the coastal plain, harvested shellfish and other estuarine resources. Based on an accumulation of paleoecological data from elsewhere in the lowland Neotropics of Mesoamerica, southern Central America and South America we pose and provide a first test of an alternative subsistence model: that the Archaic Period populations in this area were slash and burn farmers. Burned maize phytoliths first appear in these sedimentary records at 6500 cal BP in association with macroscopic charcoal and forest disturbance plant taxa. Periodic burning and forest disturbance, consistent with farming activities, are also evident in the macroscopic charcoal record between 6500 and 4700 cal BP. Pollen, phytolith and charcoal records all point to sustained burning, forest disturbance and the cultivation of maize between 4700 and 3800 cal BP. These data suggest that people were slash and burn farming during the Archaic Period prior to the adoption of pottery and the proliferation of Early Formative Period villages and full-fledged agriculture based on near or total reliance on crop plants after ∼3800 cal BP.