Isothermal Time‐Series Determination of the Rate of Diffusion of Water in Pachuca Obsidian*

Friedman and Smith's (1960) article introducing an exciting, potentially precise and inexpensive method of dating obsidian artefacts has thus far failed to reach its potential. Numerous efforts to refine, improve and even redevelop the method since that time have similarly failed to achieve the original promise. Only within the last eight years have significant improvements been made, due to both improved analytical techniques and a better understanding of the hydration process. However, most of our mechanistic understanding of the interaction of water with rhyolitic glass is based on experiments performed on melts and glasses at temperatures above their glass transitions, conditions inappropriate for investigation of near‐surface environmental conditions. Unfortunately, studies detailing the temporal evolution of the diffusion profile at low temperatures are rare, and few useful data are available on the low‐temperature diffusive hydration of silicate glasses. This paper presents data on the experimental hydration of obsidian from the Pachuca source (a.k.a. Sierra de las Navajas, Basin of Mexico) at 75°C for times ranging from 3 to 562 days, and compares these results with data for samples obtained from a stratigraphic excavation of the Chalco site in the Basin of Mexico. Samples have been analysed using secondary ion mass spectrometry (SIMS) to provide concentration/depth data. While 75°C is still significantly above the temperatures at which archaeological obsidians hydrate, it is well below the glass transition temperature (approx. 400°C) and thus processes are likely to be similar to those that occur in nature, but fast enough to be observed over a laboratory timescale. The results demonstrate that a simple square‐root‐of‐time model of the evolution of the diffusion profile is not adequate to describe the diffusion process, as measured diffusion profiles exhibit the effects of concentration‐ and time‐dependent, non‐Fickian diffusion. With progressive hydration, characteristic diffusion coefficients first decrease, then increase with time. Surface concentration increases with time, but an intermediate plateau is observed in its time evolution that is consistent with results obtained from the suite of Chalco samples. Both of these effects have been observed during diffusion in glassy polymer systems and are associated with the build‐up and relaxation of self‐stress caused by the influx of diffusing material.     

CHARACTERIZATION OF ARCHAEOLOGICAL AND IN SITU SCOTTISH WINDOW GLASS

Scottish window glass from both archaeological sites and historic buildings was examined using portable X‐ray fluorescence (pXRF) and scanning electron microscopy – energy‐dispersive X‐ray micro‐analysis (SEM–EDX). The elemental composition of the glass provides information regarding the materials used and, subsequently, an approximate range of dates of manufacture. pXRF is shown to be more vulnerable than SEM–EDX to the effects of surface corrosion and matrix effects in archaeological samples. The study showed that the production of window glass in Scotland from the 17th century onwards appears to closely parallel that in England. It also demonstrated the potential of pXRF for in situ studies of window glass in historic buildings. pXRF was used to assess two Scottish buildings; one in state care and one in private ownership. The building in state care, the Abbot's House at Arbroath Abbey, showed a uniform glass type, suggesting that the building was re‐glazed completely at some point during the late 19th or early 20th century. The building in private ownership, Traquair House, had a range of glass types and ages, demonstrating a different maintenance and repair regime. This type of data can be useful in understanding historic buildings in the future, particularly if re‐glazing is being considered.     

THE BLUE ENAMELS IN THE BAROQUE DECORATIONS OF THE CHURCHES OF PALERMO,SICILY: FE2+‐COLOURED GLASSES FROM LIME KILNS*

Deep blue glasses coloured by octahedral Fe²⁺ cations are often reported as textbook examples of blue pigmentation. However, despite the possibility of laboratory synthesis under reducing conditions, to date there are no well‐reported occurrences of their production and use in the past. A thorough historical, ethnographic, mineralogical, and chemico‐physical investigation of the ‘smaltini di calcara’ from several baroque churches in Palermo, Sicily, has revealed that the blue enamels widely used for altar decorations in the 17th and 18th centuries are actually a unique case of ancient blue glasses pigmented by divalent iron cations in distorted octahedral coordination. This mixed‐alkali glass was accidentally produced under severely reducing conditions in the local kilns during production of lime.     

Chemical Analysis of 17th‐century Red Glass Trade Beads from Northeastern North America and Amsterdam

Seventeenth‐century opaque red (redwood) glass trade beads of different shapes and sizes were made of mixed alkali (mainly soda)–lime glasses and were coloured with Cu, presumably as cuprous oxide or as finely dispersed elemental Cu. During the early 17th century, beads of all shapes were opacified with Sn; cored beads, with uncoloured cores and hence lower Cu levels, also tended to have slightly lower Sn contents than uncored beads. By the mid‐17th century, cored tubular beads were being opacified with a combination of Sn and Sb, a technological change similar to that observed in white glass trade beads, while uncored redwood beads appear not to have been opacified with either Sn or Sb. Bead chemistries are sufficiently different to allow them to be sorted into subgroups, which may then be tracked in various archaeological sites and regions.     

DISCOVERY,PRODUCTION AND USE OF TIN‐BASED OPACIFIERS IN GLASSES,ENAMELS AND GLAZES FROM THE LATE IRON AGE ONWARDS: A REASSESSMENT*

Tin‐based opacifiers (lead stannate yellow and tin oxide white) were first used in glass production for a short period in Europe from the second to the first centuries bc , and then again throughout the Roman and Byzantine Empires from the fourth century ad onwards. Tin oxide was also used in the production of Islamic opaque glazes from the ninth century ad , and subsequently in enamels applied to Islamic and Venetian glasses from the 12th century ad onwards. A selection of published analytical data for the tin‐opacified glasses, enamels and glazes is summarized, and the methods used in their production are reassessed. The phase transformations occurring when mixtures of lead oxide, tin oxide and silica are fired are investigated with high temperature X‐ray diffraction (XRD) using a synchrotron radiation source, and these results are used to explain the observed differences in the glass, enamel and glaze compositions. Possible reasons for the use of tin‐based opacifiers in the second to first centuries bc , and for the switch from antimony‐ to tin‐based opacifiers in the fourth century ad are suggested, and the possible contexts in which tin‐based opacifiers might have been discovered are considered. The introduction of tin‐opacified glazes by Islamic potters in the ninth century ad is discussed in terms of technological transfer or independent invention.     

1H‐NMR AND 31P‐NMR CHARACTERIZATION OF THE LIPID FRACTION IN ARCHAEOLOGICAL OINTMENTS

Lipids are a broad group of naturally occurring molecules, which includes fats, oils, waxes, sterols, terpenes, fat‐soluble vitamins, monoglycerides, diglycerides, phospholipids and others. Lipids have been widely used in human history and they are often present in archaeological finds. In particular, in the field of medicine and cosmetics, lipids have been employed as base in the preparation of unguents, salves and balms. The characterization of these products and their degradation products induced by ageing is important for an understanding of the ancient pharmaceutical techniques and to assess the state of conservation. ¹H‐NMR and, for the first time, ³¹P‐NMR spectroscopy have been applied to the characterization of such compounds. By derivatization of the samples with 2‐chloro‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaphospholane, it is possible to recognize, quantify and evaluate the degradation degree of lipids in archaeological unguent samples. With this new approach, lipids have been recognized in 17th‐century archaeological ointments from the Aboca Museum. Moreover, severe hydrolysis and oxidation markers have been detected.     

Radical changes in Islamic glass technology: evidence for conservatism and experimentation with new glass recipes from early and middle Islamic Raqqa,Syria*

The chemical analysis of excavated glass fragments from dated archaeological contexts in Raqqa, Syria, has provided a detailed picture of the chemical compositions of artefacts deriving from eighth to ninth and 11th century glassmaking and glassworking activities. Evidence for primary glass production has been found at three excavated sites, of eighth to ninth, 11th and 12th century dates; the first two are discussed here. The 2 km long industrial complex at al‐Raqqa was associated with an urban landscape consisting of two Islamic cities (al‐Raqqa and al‐Rafika) and a series of palace complexes. The glass fused and worked there was presumably for local as well as for regional consumption. Al‐Raqqa currently appears to have produced the earliest well‐dated production on record in the Middle East of an Islamic high‐magnesia glass based on an alkaline plant ash flux and quartz. An eighth to ninth century late ‘Roman’/Byzantine soda–lime recipe of natron and sand begins to be replaced in the eighth to ninth century by a plant ash – quartz Islamic soda–lime composition. By the 11th century, this process was nearly complete. The early Islamic natron glass compositional group from al‐Raqqa shows very little spread in values, indicating a repeatedly well‐controlled process with the use of chemically homogeneous raw materials. A compositionally more diffuse range of eighth to ninth century plant ash glass compositions have been identified. One is not only distinct from established groups of plant ash and natron glasses, but is believed to be the result of experimentation with new raw material combinations. Compositional analysis of primary production waste including furnace glass (raw glass adhering to furnace brick) shows that contemporary glasses of three distinct plant ash types based on various combinations of plant ash, quartz and sand were being made in al‐Raqqa during the late eighth to ninth centuries. This is a uniquely wide compositional range from an ancient glass production site, offering new insights into the complexity of Islamic glass technology at a time of change and innovation.     

SIMS‐SS,A NEW OBSIDIAN HYDRATION DATING METHOD: ANALYSIS AND THEORETICAL PRINCIPLES*

The water diffusion mechanism in obsidian has been revisited with the advent of a new dating approach employing secondary ion mass spectrometry (SIMS). The water diffusion SIMS(+) profile and the concept of a surface saturation (SS) layer in obsidians both provide a sound basis for the new diffusion age equation (SIMS‐SS) and are supported by dated world examples ( Liritzis et al. 2004 ). Here, we present the basic physical–chemical analysis of the mass transport phenomenon on which the new dating method is based. The crucial age parameter of the SIMS‐SS dating approach for archaeological obsidians—that is, the surface saturation (SS) layer—is supported by both theoretical and experimental data.     

A chronometric tool for Hawaiian archaeology: the hydration dating of Pu'u Wa'awa'a trachytic glass

The Pu'u Wa'awa'a trachytic glass deposit located on the Big Island of Hawai'i was a source of lithic tools for much of Hawaiian prehistory. Routinely encountered at habitation sites, the glass has the potential to provide absolute dates based upon the degree of surface hydration. Infrared photoacoustic spectroscopy and secondary ion mass spectrometry were used to monitor the diffusion of water in archaeological and experimental samples. Accelerated laboratory hydration experiments show that water diffusion in trachytic glass containing a structural water content of 0.16% ± 0.03% is linear with time. Application of the calibration to trachytic glass artifacts from the Kahalu'u habitation cave have produced chronometric dates in the 17th–18th centuries. These age estimates are in agreement with radiocarbon dates and artifactual data that bracket the site occupation. However, the glass dates do not correlate well with site stratigraphy and this suggests that slight sample imperfections that retain water may be one factor that results in ages that are too early for later occupation levels.     

Portuguese Blue‐on‐Blue 16th–17th Century Pottery

Blue‐on‐blue (‘berettino’) sherds have appeared in numerous production and consumption archaeological excavations in Lisbon and other archaeological sites in Portugal (dated from the mid‐16th century to the beginning of the 17th century). The abundance of this interesting faience led us to compare it with similar pottery from other well‐known production centres in Italy, namely Liguria (Savona and Albisola), Spain (the Triana kilns) and the Low Countries. Differences in the diffraction patterns of the sherds' pastes from the four countries were observed. In most samples, cobalt blue silicate (cobalt olivine) was identified in the dark blue or light blue glazes through the use of micro‐Raman spectroscopy and diffuse reflectance spectra. A remarkable difference in the calcite contents of the Lisbon and Seville pottery sherds was observed, in accordance with previous observations of high calcite contents of Seville ceramics. A comparison was also made for all of the blue‐on‐blue sherds studied here with many other 16th–17th century sherds from Lisbon using bivariate plots of K/Si versus Ca/Si. Lisbon and Seville pottery behave very differently, whereas sherds from Italy and the Low Countries occupy intermediate positions.     

WASTE GLASS,VESSELS AND WINDOW‐PANES FROM THAMUSIDA (MOROCCO): GROUPING NATRON‐BASED BLUE–GREEN AND COLOURLESS ROMAN GLASSES

A collection of window‐panes, vessels and alleged waste from Thamusida has been investigated by OM, SEM–EDS, ICP–MS, ICP–OES and XAS at the Fe–K and Mn–K edges. Glass samples have been characterized as natron‐based soda–lime–silica glasses, with low magnesium and low potassium. The results have been compared with 43 reference groups available for ‘naturally coloured’ and colourless glasses of both Roman and later ages. Two main types were distinguished: RBGY 1 (R oman B lue–G reen and Y ellow 1) and RBGY 2 (R oman B lue–G reen and Y ellow 2). Given their compositional similarity to the Levantine I or, to a lesser extent, HIMT glasses, the Syrian–Palestinian coast for RBGY 2 and Egypt for the RBGY 1 have been suggested for their provenance. Most Thamusida samples have been assigned to the RBGY 2 type. A small group of Thamusida colourless vessels was included into the RC (R oman‐C olourless) compositional field; the latter still being defined. The alleged waste pieces may define a local production that should have been of secondary type. The investigations performed on local raw materials seem to discount the possibility of a primary glass‐making site. XAS measurements determined that Fe²⁺ contents ranging between 30 and 52% are able to assure an aqua blue colour; below 30%, the glasses turn light green or light yellow.     

ARCHAEOLOGICAL,STYLISTIC AND SCIENTIFIC RESEARCH ON 11TH–13TH CENTURY AD PAINTED FRAGMENTS FROM THE SAN GIOVANNI BATTISTA CHURCH IN CEVIO (SWITZERLAND)

The painted fragments collected during the archaeological excavation campaign in the San Giovanni Battista church in Cevio represent a unique patrimony of Romanesque wall painting in Tessin, Switzerland, having a strong stylistic linkage with the Lombardic art of the same period. The archaeological and stylistic research allowed the fragments to be dated between the 11th and 13th centuries ad and to group them in three chronological phases. The scientific research (p‐XRF, OM, SEM–EDS, FTIR and XRD) was aimed at characterizing the pigments and the pictorial techniques used. Important changes occurred in terms of some pigments used during the 11th and 12th centuries: in particular, azurite was used to decorate the earlier wall paintings while lapis lazuli was used for the 12th‐century ones. During the second period, lead‐based pigments (lead white and minium) were introduced into the palette. The use of natural yellow and red ochres and green earth was common for the three periods. The fresco technique was generally used, except for the application of azurite and lead‐based pigments, where the a secco technique was adopted. The integrated research is a contribution to the knowledge of Romanesque art in the Insubric Region.     

THE APPLICATION OF A PORTABLE X‐RAY FLUORESCENCE SPECTROMETER TO THE ON‐SITE ANALYSIS OF GLASS VESSEL FRAGMENTS FROM SOUTHERN THAILAND*

Ancient glass vessel fragments belonging to the seventh to ninth centuries ad , from the Ko Kho Khao, Laem Pho and Khuan Lukpad sites in southern Thailand, were studied. The glass vessel fragment samples are a collection belonging to the Department of Archaeology, the 15th Regional Office of Fine Arts of Thailand. The chemical compositions of the glasses were analysed using a modified portable energy‐dispersive X‐ray fluorescence spectrometer (OURSTEX 100FA‐II) by the introduction of a MOXTEK^® AP3.3 polymer window (5 mm²?) to the KETEK silicon drift detector for the measurement of light elements. The non‐destructive analysis was performed at the National Museum, Phuket, in Thailand. It is shown that the glass chemical compositions belong to mineral and plant‐ash based soda–lime–silicate glass. The origins of the glass artefacts are discussed in terms of raw materials and glass decoration, and compared with previously reported similar typological glasses from sites in the port city of Rāya and the Monastery of Wadi al‐Tur in Egypt.     

SCIENTIFIC ANALYSIS OF SEVENTH‐CENTURY GLASS FRAGMENTS FROM THE CRYPTA BALBI IN ROME*

Inductively coupled plasma emission spectroscopy, reflectance spectroscopy and X‐ray diffraction were used to study seventh‐century AD glass fragments from the Crypta Balbi in Rome. All the samples were found to be silica‐soda‐lime glasses. Iron determines the colour of blue‐green, green and yellow‐green transparent glasses; chemical composition suggests deliberate addition of iron and/or manganese in about half the samples. Copper was found as the main colourant in red, pale blue and blue‐green opaque fragments; elemental copper acts as an opacifier in red glass, and calcium antimonate in white, pale blue and blue‐green glasses. Detection of antimony in transparent fragments suggests recycling of opaque mosaic tesserae.     

‘The Ghost Ship’. An Intact Fluyt from c.1650 in the Middle of the Baltic Sea

We report an exceptionally well preserved 17th‐century shipwreck in the Baltic Sea. The investigation of the intact 3‐dimensional hull at 130 m depth in the cold dark water has demanded new methods of documentation. Field investigation of ‘The Ghost Ship’ has been done in co‐operation with a nautical survey company, combining archaeological skills with advanced technology and filming for a television documentary. The discovery offers detailed knowledge about Dutch shipbuilding and the construction of fluyts. We also believe that study of the social organisation aboard this small trading ship can give insights into the mentality and ideology of the period. © 2012 The Authors     

Chemical analysis of 17th century Millefiori glasses excavated in the Monastery of Sta. Clara-a-Velha,Portugal: comparison with Venetian and façon-de-Venise production

A set of ten Millefiori glass fragments dating from the 17th century, originated from archaeological excavations carried out at the Monastery of Sta. Clara-a-Velha (Coimbra, Portugal), were characterized by X-ray electron probe microanalysis (EPMA), Raman microscopy and UV–Visible absorption spectroscopy. All glasses are of soda-lime-silica type. The use of coastal plant ash is suggested by the relatively high content of MgO, K₂O and P₂O₅, as well as by the presence of chlorine. Tin oxide or calcium antimonate were the opacifiers used in the opaque glasses, cobalt in the blue glasses, copper in the turquoise glasses, iron in the yellow and greenish glasses, and iron and copper were found in the opaque red and aventurine glasses. Based on the concentrations of alumina and silica four different sources of silica were identified, allowing the classification of the glasses into the following compositional groups: low alumina (<2 wt%), which includes a sub-group of cristallo samples with SiO₂ > 70 wt%, medium alumina (2–3 wt%), high alumina (3–6 wt%) and very high alumina (>6 wt%). Comparison with genuine Venetian and façon-de-Venise compositions showed that two fragments are of Venetian production, one of Venetian or Spanish production and the remaining are of unknown provenance. In two fragments the glass of the decoration is probably Venetian or Spanish but the glass used in the body is also of unknown provenance.     

Admiral: a 19th‐century Tyne‐built paddle tug

This paper reports on the discovery in the Thames Estuary and the partial recovery and recording of the remains of a 19th‐century Tyne‐built paddle tug. The wreck is believed to be that of Admiral built in Newcastle in 1870 and sunk following a collision in the estuary in 1872. This unexpected discovery provided a rare opportunity to examine the archaeological assemblage of one these once‐familiar working vessels and revealed the continuities and innovations of a specific type of engine used on paddle tugs.     

Analysis of Medieval and Post‐Medieval Glass Fragments from the Dubrovnik Region (Croatia)

Dubrovnik was an important trade city throughout the medieval and post‐medieval time period, maintaining its own glass production from the 14th to the 16th century. Unfortunately, Dubrovnik glass discoveries have not been well investigated up until now, except via archival data in large data analyses. In the following work, we will shed new light on the glass material found in this region, which has diverse origins, chronology, typology and style. Medieval and post‐medieval glass finds (10th/12th–18th centuries) discovered during archaeological excavations in Dubrovnik and the Dubrovnik region were analysed using particle‐induced X‐ray emission (PIXE) and particle‐induced gamma‐ray emission (PIGE), which revealed three main compositional groups: natron glass, plant‐ash glass and potash glass. This demonstrates the important commercial links present between Dubrovnik and other major glass‐making centres.     

Strontium Isotopes in the Investigation of Early Glass Production: Byzantine and Early Islamic Glass from the Near East*

⁸⁷Sr/⁸⁶Sr ratios have been determined for glasses from four production sites, dated to between the sixth and the 11th centuries, in the Eastern Mediterranean region. On the basis of elemental analyses, the glasses at each location are believed to have been melted from different raw materials. Two glass groups, from Bet Eli‘ezer and Bet She‘an, in Israel, are believed to have been based upon mixtures of Levantine coastal sands and natron, and have ⁸⁷Sr/⁸⁶Sr ratios close to 0.7090, plus high elemental strontium, confirming a high concentration of modern marine shell (⁸⁷Sr/⁸⁶Sr ~ 0.7092) in the raw materials. The isotopic compositions of these two groups of glasses differ slightly, however, probably reflecting a varying ratio of limestone to shell because the sands that were utilized were from different coastal locations. Natron‐based glasses from a workshop at Tel el Ashmunein, Middle Egypt, have ⁸⁷Sr/⁸⁶Sr values of 0.70794–0.70798, and low elemental strontium, consistent with the use of limestone or limestone‐rich sand in the batch. High‐magnesia glasses based on plant ash, from Banias, Israel, have ⁸⁷Sr/⁸⁶Sr values of 0.70772–0.70780, probably reflecting the isotopic composition of the soils that were parental to the plants that were ashed to make the glass. Strontium and its isotopes offer an approach to identifying both the raw materials and the origins of ancient glasses, and are a potentially powerful tool in their interpretation.