Archaeological Glass Research Articles

Provenance studies of 18th century potassium-rich archaeological glass from Portugal

The archaeometric study of a group of colourless glass fragments recovered from two archaeological excavations performed in Lisbon, Portugal is here reported. The archaeological interventions were performed at Rua do Arsenal (LRA), where the ruins of the Côrte-Real Palace were partially discovered, and at the Roman Theatre Museum (LTR), where the remains of a middle-class house dated to the 18th century were found. The recovered glass fragments are dated between the end of the 17th century and the 18th century, and were chemically characterised with the aim of discussing its provenance. Micro particle induced X-ray emission (μ-PIXE) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were the chosen analytical methods to characterise the glass composition. All twenty-five fragments proved to be of a potassium-rich composition, where the choice of raw materials seems to have been made with extreme care. This is reflected in general by a composition with low levels of impurities, such as alumina and iron oxide, and high levels of silica.Two compositional groups were identified, that besides differing in other components have different contents of arsenic oxide. None of the groups could be undoubtedly compared with the few known potassium-rich compositions from coeval glass production centres in Europe. The majority of the analysed samples could only be compared, in terms of major oxides, with the potassium-rich production from the Coina Glass Factory in Portugal.

Experimental mixing of natron and plant ash style glass: implications for ancient glass recycling

The practice of re-melting glass was well known, certainly from the Roman period onwards. This can be seen not only in ancient literary evidence but also in the archaeological evidence, collections of broken glass have been found in, for example, Pompeii (79 AD) and the Iulia Felix shipwreck (Third century AD). Elevated levels of certain transition metals in archaeological glasses are interpreted as indications of the mixing and/or recycling of different glasses. Assumptions have been made that all glasses could be recycled, but to what extent are these valid? Why does the evidence for the recycling of glass only occur from the Roman period onwards? From the middle of the First millennium BC to the Ninth century AD, natron glass was the predominant glass type in the Mediterranean and Europe, however, plant ash glass was still in use in some areas. To test the effects on the final product of mixing different composition glass types, experimental glasses were made by mixing varying quantities of replica plant ash glass, replica natron glass, and a modern glass. At low temperatures crystalline material formed in the products containing replica plant ash glass. As the plant ash glass content increased, so too did the amount of crystalline material produced. This is due to a combination of the glass compositions and the firing temperature. It appears that natron type glass can be more easily recycled at lower temperatures, although, if a high enough temperature is used then most glass types can be recycled. Early furnace technology, i.e. the vertical heating chamber furnace, may not have been able to achieve these high temperatures, hence the widespread practice of recycling did not begin until after the invention of glassblowing which required a change in the furnace technology to the use of a horizontal heating chamber furnace.

Understanding the mechanisms of Si–K–Ca glass alteration using silicon isotopes

It is important to understand glass alteration mechanisms and to determine their associated kinetics in order to develop models able to predict the alteration of nuclear, basaltic or archaeological glasses. Recent studies revealed that the respective contributions of diffusion, dissolution, condensation and precipitation processes in alteration are still a matter for debate. In this work, the alteration of a medieval-type glass (Si–K–Ca) was investigated as it presents a specific composition (without B and with low Al). Experiments were performed using a dynamic device, at 30°C, at pH 8 and 9 and during 1month in order to simulate alteration in contact with water (rainfall or condensation). The solution was doped in 29Si to discriminate between the silicon from glass (mainly 28Si) and from solution. The results showed that the external region of the alteration layer is devoid of modifier cations (K, Ca) and presents a 29Si/28Si ratio close to the solution one. This excludes that the alteration layer is a glass skeleton and highlights a progressive hydrolysis/condensation process, even if non-hydrolyzed silica tetrahedra could remain when the Si isotopic equilibrium is not reached. The internal zone appears to be gradually depleted in modifier cations and partly enriched in 29Si, but the thickness of this zone is overestimated using SEM-EDS and SIMS techniques. Even if in these experiments the dissolution mechanism is favored, the contribution of interdiffusion cannot be neglected to explain the weathering of ancient stained glassed windows in the atmosphere. The respective contribution of diffusion and dissolution are also discussed as a function of glass composition and surface texture, as well as of experimental conditions (alkaline pH, renewal of the solution).

Glassmaking using natron from el-Barnugi (Egypt); Pliny and the Roman glass industry

Pliny the Elder describes the discovery of a process for making natron glass, which was widely used for much of the first millennium bc and ad. His account of glassmaking with natron has since been corroborated by analyses of archaeological glass and the discovery of large-scale glass production sites where natron glass was made and then exported. Analyses of Egyptian natron have shown it to be a complex mixture of different sodium compounds, and previous experiments to make glass with Egyptian natron have been unsuccessful. Here, natron from el-Barnugi in the Egyptian Nile delta, a site which also probably supplied Roman glassmakers, is used to produce glass. The experiments show that high-quality glass, free of unreacted batch or bubbles, could have been produced from natron in its unprocessed form in a single stage, that larger quantities of natron would be required than has previously been anticipated, that the presence of different sodium-containing compounds in the deposit aided melting, and that negligible waste is produced. The implications for the identification of glass production sites, for the organisation of trade and for the supply of natron within and outside Egypt are discussed in the light of Pliny’s accounts.

Electrochemical Fingerprint of Archeological Lead Silicate Glasses Using the Voltammetry of Microparticles Approach

The application of a solid‐state electrochemical technique, voltammetry of microparticles (VMP), for studying archeological lead glass is described. Upon attachment to graphite electrodes immersed into aqueous acetate buffer, characteristic voltammetric profiles were obtained for submicrosamples of archeological glasses dated between the 9th and 19th centuries. Bivariate and multivariate chemometric analyses of the VMP data allowed us to characterize individual workshops/provenances which enabled a clear discrimination between soda‐rich and potash‐rich glasses. An analysis of the VMP data, combined by XRF, FESEM, AFM and ATR‐FTIR and Micro‐Raman spectroscopies, denoted the presence of Pb(IV) centers accompanying network‐former and network‐modifier Pb(II).

Chemical characterisation of archaeological glasses from the Hellenistic site of Jebel Khalid, Syria by electron probe microanalysis

Jebel Khalid is a single period Hellenistic site on the west bank of the Euphrates River in northern Syria. The occupation of the site dates from the early 3rd century BCE until its abandonment in the late 70s BCE. The so-called Governor’s Palace, an administrative centre on the Acropolis of the site, overlooked this walled Greek garrison city. A considerable quantity of glass, predominantly drinking bowls, was excavated from this building complex. This study concerns the elemental analysis of glass samples from this assemblage by electron probe microanalysis (SEM-WDS). The preliminary analyses presented in this report reveal that the Jebel Khalid glasses are of the silica-soda-lime type fluxed with mineral soda, typical of late 1st millennium BCE glass composition. Manganese was employed as the chief decolourant. Glass compositions of monochrome bowls, core-formed and mosaic glass vessels are very similar, despite the different forms, colours and manufacturing techniques of the vessels. While the production centre for the Jebel Khalid glass remains elusive, the similarity to other published Hellenistic glasses from Greek mainland sites, Rhodes, Tel Anafa in Israel, and Gordion in central Turkey, indicates a tightly controlled composition with comparable batch ingredients. Without more comparative material of this date from the Near East and Greece, it is difficult to determine whether production of the vessel glass from this Seleucid site in the Near East occurred in the Aegean region or the Syro-Palestinian Levant, or both. Vessel style and archaeological context lean towards an Aegean connection, but until more comparative glass is analysed, and trace element and isotope data are considered, questions of primary and secondary production remain unresolved.

Gilding on glass: New evidence from a 17th century flask found in Portugal

In the present work, a set of archaeological glass fragments belonging to a singular 17th century glass flask with gilded decoration was sampled and analyzed. The fragments were excavated in Coimbra, Portugal. The main focus of this study is to bring to light the flask production technique, in particular the gilding process, and additionally, to investigate the object's provenance based on the composition of the glass. A comprehensive survey of ancient and traditional glass gilding techniques is also presented.The glass and the gilded areas were characterized using micro energy dispersive X-ray fluorescence spectroscopy (μ-EDXRF), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray electron probe micro-analysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).The flask is made of soda-lime-silica glass and the use of coastal plant ashes is suggested by the relatively high content of MgO and K2O, as well as by the presence of chlorine. The high alumina content excludes a Venetian provenance, and with regard to the contents of Na2O, SiO2, K2O, and CaO, the glass composition is distinct from the façon-de-Venise glasses which have been studied, and only comparable to a few 17th century millefiori glasses, also recovered in Coimbra.Lead was detected in the gilded areas suggesting that a lead based mordant was used in the gilding process to promote the adhesion of the gold leaf to the glass during the low temperature reheating of the object. The gold leaf composition was determined by LA-ICP-MS, and it was possible to ascertain its purity: between 22 and 23 gold carats.

Combined Spectroscopic Analysis of Beads from the Tombs of Kindoki, Lower Congo Province (Democratic Republic of the Congo).

Raman spectroscopy and X-ray fluorescence (XRF) analysis are commonly applied to archaeological objects as a fast and nondestructive way to characterize the materials. Here, micro-Raman spectroscopy and chemometrics on handheld XRF results were used to completely characterize beads found during archaeological excavations in the Congo. Metallic objects, organogenic materials, and glass beads were studied. Special attention was paid to the glassy materials, as they seem to be of European production. The matrix family and crystalline phases assemblage, as well as the results from principal components analysis on the elemental data, were used to define groups of beads of similar composition, and therefore probably of similar origin. This research project establishes the feasibility of this approach to archaeological glasses, and can be used to confirm and support the bead typologies used by archaeologists.

Geochemical heterogeneity of sand deposits and its implications for the provenance determination of Roman glass

During the production of natron glass most features of the raw materials are lost and only some bulk geochemical characteristics have potential as provenance indicators. To determine the primary origin of archaeological glass artefacts, suitable sand raw materials have to be accurately characterised. In this respect, information about the possible variation in geochemical properties within a silica source is also vital to account for potential (partial) overlap of different sources.In this study, it is shown that the variation in major and minor elemental composition of beach sand on a local scale is smaller than the variation in Roman natron glass. Therefore, a single sand deposit can be seen as a relatively homogeneous source of silica for glass production. Nd isotopic signatures are identical for all samples analysed. The isotopic composition of Sr however varies considerably due to local variations in the relative proportions of carbonates and silicates (mostly feldspar).

Compositional identification of 6th c. AD glass from the Lower Danube

A group of finds (vessels, raw glass chunks, window panes) from three sites in present-day Bulgaria was selected as representative of the circulation and usage of glass in the Lower Danube region during the 6th c. AD. In total, 79 samples were analysed by EPMA and/or LA-ICP-MS techniques. The data quality was assessed for each analytical run according to the measurement of reference glasses and to pairs of results obtained from representative samples of archaeological glass analysed by both techniques. Combining EPMA and LA-ICP-MS data allowed a sufficiently consistent and unified set of primary results to be formed. As already suggested in an earlier preliminary paper, only a single glass composition was found to dominate the 6th c. contexts in the region. The current study recognises this 6th c. glass from the Lower Danube as identical with the so called ‘Serie 2.1.’ defined by D. Foy and co-workers (2003) in various assemblages in Southern France and North Africa. The major, minor and trace oxide evidence presented here indicates that this is a distinct primary glass composition, with an iron-rich sub-group tentatively differentiated within the main group. Accordingly, an attempt is made to situate it relative to the other main primary compositions in the region. The proposed interpretation is that the 6th c. glass should not be linked to the HIMT glass despite the nominal similarity between them due to their elevated iron oxide, manganese, and titania concentrations. Instead, a possible link between the geochemical characteristics of the 6th c. glass and an earlier group of manganese decolourised glass, equivalent to ‘Serie 3.2.’ outlined by D. Foy and co-workers (2003) is suggested. This may imply the use of sand from a broadly identical geological area, hence it is possible that both the 6th c. glass and the manganese decolourised composition are likely to share a common origin.

Application of 12 MeV proton activation to the analysis of archaeological specimens

12 MeV proton activation analysis is applied to a variety of archaeological specimens (glass, pottery, mortar and ivory) and its usefulness studied. The method is non-destructive and Ca, Ti, V, Cr, Fe, Cu, Zn, As, Sr, Y, Zr and Sb, ranging from percentage to parts per million (ppm) level were determined. The detection limits in archaeological glass for Ti, V, Cr, Fe, As, Sr, Y and Zr are at 1–10 ppm level; Cu, Zn and Sb at 20–35 ppm level, and Ca at 150 ppm level.

Cyclododecane as opacifier for digitalization of archaeological glass

Abstract This paper faces the problem of acquiring archaeological artifacts using triangulation based 3D laser scanners and focusing on reflective/refractive surfaces. This kind of artifacts are mostly made of glass or polished metal, and the properties of their surfaces violate most of the fundamental assumptions made by vision algorithms. Also, the unique and fragile nature of archaeological artifacts adds an extra constraint to the acquisition process: the use of industrial whitening sprays has to be avoided, due to the physicochemical processes required to clean the surface after scanning and because the chemical properties of these sprays may damage the original object. As an alternative to them, a new way to use a common conservation material is proposed: the use of cyclododecane as a whitening spray. Thanks to its chemical stability and to the fact that it sublimes at room temperature, together with its good film-forming capabilities, a set of evaluation tests is presented to prove that the error introduced by the opaque thin layer created on the surface of the artifact is smaller than the accuracy of the 3D scanner and, thus, no acquisition errors are introduced. A comparison with general-purpose industrial whitening sprays is also presented, and achieved results show no significant differences in the quality of the resulting 3D models.

Laser ablation-ICP-MS depth profiling to study ancient glass surface degradation.

In general the analysis of archeological glass represents a challenge for a wide variety of objects because of the presence of physical and/or chemical damage on the surface of the artifact, also known as weathering or corrosion. To retrieve accurate bulk elemental information by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS), the original, pristine glass needs to be "reached", thereby penetrating the alteration layer which is often more than 10μm thick. To study this alteration layer the laser was operated in the drilling mode, either with a low (1Hz) or a high (10Hz) pulse repetition rate for a period of 50s yielding detailed spatial information for ca. 20 elements over a shallow depth (ca. 5μm) or less-detailed spatial information for 50-60 elements over a greater depth (ca. 50μm). Quantitative elemental depth profiles (in wt%) were obtained with the so-called sum normalization calibration protocol, based on summation of the elements as their oxides to 100wt%. We were able to associate the increase of SiO2 (in wt%) in the alteration layer to the volumetric mass density change in the glass as a result of depletion of Na2O and K2O. Also the interaction of the number of laser shots with the alteration layer is shown experimentally via depth measurements using profilometry. Chemical and physical changes in four ancient glass artifacts, directly and indirectly measureable by laser drilling, were studied as a function of internal and external factors such as age, composition, and exposure conditions.

Application of low temperature plasmas for restoration/conservation of archaeological objects

The low-temperature low-pressure hydrogen based plasmas were used to study the influence of processes and discharge conditions on corrosion removal. The capacitive coupled RF discharge in the continuous or pulsed regime was used at operating pressure of 100-200 Pa. Plasma treatment was monitored by optical emission spectroscopy. To be able to study influence of various process parameters, the model corroded samples with and without sandy incrustation were prepared. The SEM-EDX analyzes were carried out to verify corrosion removal efficiency. Experimental conditions were optimized for the selected most frequent materials of original metallic archaeological objects (iron, bronze, copper, and brass). Chlorides removal is based on hydrogen ion reactions while oxides are removed mainly by neutral species interactions. A special focus was kept for the samples temperature because it was necessary to avoid any metallographic changes in the material structure. The application of higher power pulsed regime with low duty cycle seems be the best treatment regime. The low pressure hydrogen plasma is not applicable for objects with a very broken structure or for nonmetallic objects due to the non-uniform heat stress. Due to this fact, the new developed plasmas generated in liquids were applied on selected original archaeological glass materials.

Restoration and Conservation of a Model of Archaeological Glass Objects Used for Medical Purposes. Museum of Islamic Art in Cairo: (Applied Study)

Restoration and Conservation of a Model of Archaeological Glass Objects Used for Medical Purposes. Museum of Islamic Art in Cairo: (Applied Study)

Restoration and Conservation of a Model of Archaeological Glass Objects Used for Medical Purposes. Museum of Islamic Art in Cairo: (Applied Study)

Restoration and Conservation of a Model of Archaeological Glass Objects Used for Medical Purposes. Museum of Islamic Art in Cairo: (Applied Study)

Suitability of the voltammetry of immobilized microparticles to detect and discriminate lead compounds in microsamples of ancient black cosmetics

Lead compounds, in the form of galena, have been used as eye cosmetics since ancient times and they still appear in traditional products. The presence of some black pigments in several archaeological glass objects gave us the opportunity to study the nature of these products, in order to evaluate the results of an electrochemical method to characterise lead compounds when only heterogeneous microsamples are available and the material requires to be as less manipulated as possible. The present paper describes the data obtained with an electroanalytical methodology (Voltammetry of immobilised microparticles, VMP), and a complementary Scanning Electron Microscopy study, to detect these lead compounds. A simple and fast characterisation method is discussed in order to be able to monitor the presence of lead compounds without previous sample preparation, directly in the solid micro-sample, and using an affordable instrumentation. PbS could be identified and distinguished from other lead compounds in cosmetics by Differential Pulse VMP in 1M NaCl medium by a set of three peaks (−0.63V, −0.44V, +0.45V) in the anodic voltammogram and two peaks around −0.65V and +0.45V in the cathodic scan. The results showed the suitability of the electroanalytical method, offering valuable information about the chemical and mineral composition of the samples using a minimum amount of material, and illustrating the advantages in terms of time consuming, cost and accessibility of the laboratory facilities.

The source of blue colour of archaeological glass and glazes: the Raman spectroscopy/SEM‐EDS answers

The founding of lapis lazuli to give blue colour to glass and glazes is more and more coming out from the most recent studies of pottery and glassware of different epochs and provenances. The recent discovery in the south of Italy (Frederick II, Melfi castle) of enamelled glass pieces including blue enamels questioned the real nature of the blue colour raw materials because the castle is built over and not far from outcrops of two volcanic rocks – haüynophire and phonolite – that contain haüyne, mineral belonging to sodalite group as lazurite, that can be blue or become blue after heating. Raman microscopy and scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy were tested in order to identify the rock used as raw material and to understand if the chromophore‐bearing mineral in the artefacts could be other than lazurite. To do this, the two volcanic rocks, lapis lazuli and archaeological glass with blue enamels, were studied. In particular, temperature‐dependent Raman measurements and Raman mappings both on single lazurite and haüyne crystals and on the rocks and the enamels were carried out also in order to investigate the colouration mechanism of haüyne. The results obtained allowed to make hypotheses about the transformations occurring in haüyne with heating and about the procedures of distinguishing the raw materials. Copyright © 2014 John Wiley & Sons, Ltd.

Herding cats – Roman to Late Antique glass groups from Bubastis, northern Egypt

Eighty-seven glass fragments from Roman and Late Antique layers at Tell Basta/Bubastis in the Eastern Nile Delta were typologically evaluated and chemically analysed to determine chronological and compositional patterns of glass use at this important Egyptian city, and how this relates to larger pattern of glass production and consumption in the first half of the first millennium AD. Bubastis is situated in geographical proximity to Alexandria, an important seaport, and at the same time close to the raw glass production areas in the Wadi Natrun and Sinai peninsula. This paper reports the first substantial set of compositional data of Roman to Late Antique glass from a settlement in northern Egypt, filling an important gap in our knowledge of glass consumption pattern in the first half of the first millennium AD. The glass from Bubastis falls into several compositional groups known already from elsewhere in the Roman and Late Antique world, including antimony- and manganese-decoloured glass and two varieties of HIMT glass. Changes in glass composition over more than 500 years are in line with earlier observations concerning changes in prevalence of these glass groups. However, compositional groups known to dominate archaeological glass assemblages elsewhere, such as Roman blue/green during the earlier part of the period under study, or Levantine I in the later period, are notably absent. For the later period, this is probably due to the proximity of Tell Basta to the suspected production region of HIMT glass in northern Sinai/Egypt. By analogy, this might indicate that the earlier Roman blue/green glass has a production origin further away from the Delta than the decolourised glasses prevailing in Bubastis. A particular vessel type, small-volume thick-walled dark green unguentaria, is made of probably Egyptian plant ash glass, indicating the existence of a specialised glassmaker during the early first millennium AD.

X-Ray Diffraction in Cultural Heritage and Archaeology Studies

X-ray powder diffraction methods have been more and more extensively used, in the last twenty years, in the characterization of different crystalline and non-crystalline materials of archaeological, historical, artistic interest. The present paper aims to discuss the use of these methods in studying different aspects related to the Cultural Heritage conservation. This purpose has been achieved by examining the results obtained during the studies carried out by the author and his collaborators on a number of objects formed by different materials, such as cellulose, paper, wood, papyrus, archaeological glasses, mosaics (non crystalline or only partially crystalline materials), ceramic, metals, their corrosion products, slags, stones, mortars, pigments (partially or almost completely crystalline materials).