Opaque Glass Research Articles

Production technology of Byzantine red mosaic glasses

The study of glass tesserae found in the excavations of the St Severo basilica at Classe, Ravenna, Italy, sixth century A.D., besides a comparison between these materials and those used for the decorations of the other churches of Ravenna built in the same epoch, has stimulated a discussion on the production technology of the red tesserae, which colour is due to the presence of metallic copper and/or cuprite (Cu2O) particles. As regards the opaque red glasses of the Iron Age, Roman and Byzantine periods, studies of English authors are particularly interesting, but the conclusions of the present study are partially in contrast with what reported in the literature that is based mainly on red enamels and much less on red mosaic glasses. For the studied Byzantine red mosaic glasses it is suggested the use of lead and lead-tin alloy scraps, besides additions of ash of the vegetal fuel, to attain the suitable reducing conditions during the melting process.

Physico-Chemical Properties, Composition, and Oxidative Stability of Olive and Soybean Oils Under Different Conditions

Commercial olive and soybean oils have been analyzed periodically in order to evaluate the influence of storage conditions on quality. The following parameters were determined every 10 days of storage: peroxide, saponification and acid values, absorption coefficients K270 and K232, phenols, chlorophylls and carotenoids contents, DPPH scavenging ability, and total antioxidant activity. Edible oils were exposed to daylight and stored at room temperature in different containers with the same surface area of exposure to air either in clear glass or opaque glass bottles. Changes in oils properties were also examined after the addition of Vit-E as an antioxidant in oil samples. The results showed a gradual loss of quality during storage, especially in clear glass bottles. The addition of the antioxidant, however, significantly reduced the deterioration and oxidation rate in the oil. The best containers for commercial packing of oil were opaque glass bottles containing antioxidant products.

Theoretical and experimental study of solar thermal performance of different greenhouse cladding materials

A theoretical nongray rigorous model was constructed to study the radiative heat transfer through different greenhouse covering materials by using Radiation Element Method by Ray Emission Model (REM2). This model was applied to find the difference in thermal performances performed by greenhouses that were covered with different claddings such as silica glass, Polyvinylchloride (PVC) and Low Density Polyethylene (LDPE) materials. By utilizing the wide-range spectral radiative properties (0.22–25μm) for these materials and taking into account the absorption and emission within the covering material, precise estimations of greenhouse temperatures have been achieved. Moreover, differences in greenhouse (enclosures) temperatures have been confirmed between the semi-transparent plastic films and opaque glass. In addition, outdoor experiments were conducted to measure how much heat can be trapped inside the three identical rectangular enclosures covered by the above mentioned materials. Enclosure inside air, ground surface and cover temperatures’ measurement showed a good agreement with the calculated ones by using the rigorous model.

Detailed modelling of flat plate solar thermal collectors with honeycomb-like transparent insulation

A detailed numerical model for flat-plate solar thermal collectors based on one-dimensional finite volume techniques was recently presented, see Cadafalch (2009). The model considers a solar thermal device as a pile of components represented by one or several layers characterized by thermal inertia, internal energy generation and heat transfer to neighboring layers. A multi-layer model is then used to evaluate the full flat-plate solar thermal device. The model permits to investigate any configuration and material by combining appropriate layers. Standard components as opaque insulation, absorbers, air-gaps and glasses were addressed in Cadafalch (2009).Here, a numerical model to evaluate honeycomb-like transparent insulation material in the covers as a component of the multi-layer model is discussed in detail. The honeycomb is evaluated coupling radiation, convection and conduction phenomena. The discret ordinate method is used to evaluate media participation in thermal radiation.A comparison of numerical and experimental results is presented and discussed in order to show evidence of the model credibility.

Fabrication of transparent sintered ZnO-B2O3-Bi2O3 glass body by pressureless firing and hot isostatic pressing

The optimum conditions for the fabrication of transparent glass body in the ZnO-B2O3 (ZB) and ZnO-B2O3-Bi2O3 (ZBB) systems were examined by a pressureless firing and subsequent oxygen-supplied hot isostatic pressing (HIP). The pressurelessly-fired opaque ZB glass body possessed the maximum relative density (99.1%) when fired at 620°C for 15 min in air, and was hot isostatically pressed at 630°C for 12 h under the pressure of 150MPa (80%Ar – 20%O2 atmosphere) to eliminate the residual pores; the light transmittance of this glass body was in the range of 35 to 51% (380 to 800 nm). In order to fabricate the transparent glass body at lower temperature, the fabrication conditions of ZBB glass body were examined. The pressurelessly-fired ZBB glass body possessed a maximum relative density (98.8%) when fired at 500°C for 2 h in O2 atmosphere and hot isostatically pressed at 490°C for 12 h; the transmittance of the transparent ZBB glass body was in the range of 48 to 58% (500 to 800 nm).

Effects of nucleating agents on crystallization and microstructure of fluorophlogopite mica-containing glass–ceramics

The alteration of crystallization behavior, microstructure, and thermal properties of fluorophlogopite mica-containing glass–ceramics by nucleating agent is systematically studied. TiO2, TiO2 + ZrO2, and ZrO2 have been doped as the nucleating agents in the SiO2–MgO–Al2O3–B2O3–K2O–MgF2 (BMAPS) glass system and prepared by the melt-quench technique. The glass without nucleating agent is also prepared to ascertain the influence of nucleating agent. Addition of nucleating agents effectively increases the softening as well as glass transition temperatures. From the DSC study, it is found that the fluorophlogopite mica crystallization exotherm exhibited in the temperature range 800–850 °C and the activation energy varies in the range 167–182 kJ/mol. The opaque mica glass–ceramics are derived from these BMAPS glasses by a controlled heat treatment process and heat treatment at 1050 °C is found to be optimum. The mica crystals were identified as fluorophlogopite for all the four BMAPS glasses by X-ray powder diffraction (XRD) and subsequently confirmed by FTIR spectroscopy. Excellent matching with fluorophlogopite crystal was obtained in Zirconia-containing glass–ceramic as perceived from the XRD and FTIR studies. The microstructure of interlocked card-like mica flake crystals is found to form as seen from scanning electron microscopy, and such microstructure is obtained when ZrO2 has been used as nucleating agent. Glass–ceramic without nucleating agent possesses Vickers hardness value 4.58 Gpa and it is increased with addition of the nucleating agent (5.67–6.56 GPa), ZrO2-containing glass–ceramic possess lower hardness (5.67 GPa) and better machinability. Therefore, ZrO2 is the most efficient nucleating agent to generate fluorophlogopite mica in these glass–ceramics useable for SOFC applications.

Production technology and replication of lead antimonate yellow glass from New Kingdom Egypt and the Roman Empire

Lead antimonate was used to produce opaque yellow glasses from the beginnings of glass production in the Near East and Egypt around 1500 BC through into the Roman period. The composition and crystallographic structure of lead antimonate particles present in a small group of New Kingdom Egyptian and Roman glasses were investigated using analytical scanning electron microscopy and X-ray diffraction. The results showed that the particles were of the type Pb2Sb2O7 with a cubic structure and with the antimony partially replaced by iron and zinc in the case of the Egyptian glass, and by iron and tin in the case of the Roman glass. Synthesis in the laboratory of lead antimonate pigments, animes (i.e., lead–antimony–silica mixtures) and yellow glasses established that New Kingdom Egyptian and Roman yellow glasses could have been produced by stirring, respectively, lead antimonate pigment or anime, containing excess lead oxide, into a molten colourless glass. It is further shown that yellow lead antimonate particles are stable in glass up to operating temperatures in the range 900–1000 °C before converting to white calcium antimonate, and that their stability is enhanced by incorporating small amount of impurities such as iron, zinc and tin. The effect of different synthesis parameters and compositions on the colour of the glasses is investigated using UV–vis reflectance spectrometry.

Evaluation of optical properties and thermal performances of different greenhouse covering materials

An inverse method was conducted to obtain the spectral optical properties of four greenhouse covering materials, (Low Density Polyethylene (LDPE), Polyolefin (PO), Polyvinylchloride (PVC) and Fused Silica Glass). Diffuse reflectance and transmittance of the covering materials were measured using spectrophotometric method; the complex index of refraction in the range between 0.22 and 25μm was deduced by inverse calculation using Radiative Element Method by Ray Emission Model (REM2). At longwave radiation, the optical constants of opaque glass material were found by utilizing Kramers–Kronig method resulting good correlation with results obtained by other investigations. A rigorous model for radiative heat transfer analysis to an agricultural greenhouse was developed. The greenhouse covering material was analyzed as a non-gray one-dimension plane-parallel medium subjected to solar and thermal irradiation using REM2. Specular reflectance and diffuse incident irradiation were treated at the boundary surfaces and absorption and emission were taken into account. Thermal performance was evaluated for the above mentioned covering materials.

Technical Note: Comparing von Luschan skin color tiles and modern spectrophotometry for measuring human skin pigmentation

Prior to the introduction of reflectance spectrophotometry into anthropological field research during the 1950s, human skin color was most commonly classified by visual skin color matching using the von Luschan tiles, a set of 36 standardized, opaque glass tiles arranged in a chromatic scale. Our goal was to establish a conversion formula between the tile-based color matching method and modern reflectance spectrophotometry to make historical and contemporary data comparable. Skin pigmentation measurements were taken on the forehead, inner upper arms, and backs of the hands using both the tiles and a spectrophotometer on 246 participants showing a broad range of skin pigmentation. From these data, a second-order polynomial conversion formula was derived by jackknife analysis to estimate melanin index (M-index) based on tile values. This conversion formula provides a means for comparing modern data to von Luschan tile measurements recorded in historical reports. This is particularly important for populations now extinct, extirpated, or admixed for which tile-based measures of skin pigmentation are the only data available.

Glass from the Archaeological Museum of Adria (North-East Italy): new insights into Early Roman production technologies

In the present study, the first archaeometric data on an ample selection of intentionally coloured (or decoloured) Early Roman glass (1st–2nd centuries AD) from the Archaeological Museum of Adria (Rovigo, Italy) are reported. The analysed samples are 61 in total, both transparent and opaque, and were characterised from the textural (SEM-EDS), mineralogical (XRPD) and chemical (XRF, EPMA, LA-ICP-MS) points of view. This combined approach allowed us to identify the raw materials and production technologies employed in the manufacture of glassware. Results for the transparent samples show that they are all silica-soda-lime glasses. Most of them, independently of colour, have compositions close to those of typical Roman glass, produced with natron as flux. No relationships were identified among chemical compositions, types or production techniques, but a dependence on bulk composition was identified for some particular colours, revealing the careful and intentional selection of raw materials. This is the case of Sb-colourless glass, produced with sand of high purity, a group of intensely coloured objects, mainly emerald green and black, produced with soda ash as flux, and some blue examples produced with various sources of sand or soda ash as flux. Two main types of opacifiers were identified for the opaque samples: calcium antimonate for white, mauve and blue glasses, and lead antimonate for the yellow ones; in one case, a yellow lead-tin antimonate was also identified. As regards the opaque glasses, most of the samples opacified with calcium antimonate are silica-soda-lime in composition, similar to the typical Roman glass. Instead, samples opacified with lead and/or lead-tin antimonates are lead glasses, suggesting different production technologies.

Distinguishing between Apollo 14 impact melt and pristine mare basalt samples by geochemical and textural analyses of olivine

Apollo 14 (A-14) impact melt olivine vitrophyres (OVs), composed of olivine phenocrysts in an opaque glass matrix with minor amounts of pyroxene and plagioclase, are petrographically similar to pristine quenched A-14 high-alumina (high-Al) and Apollo 12 (A-12) basalts. Textural and chemical analyses have been conducted on olivines within impact melt and pristine mare basalt clasts from A-14 breccia 14321 as well as various olivine-phyric Apollo 12 and 17 basalts to be able to distinguish between the petrographically similar samples. The A-14 high-Al basalts examined here represent samples from each of the three chemical groups (A, B, C). Examples from the three A-12 basalt suites (Ilmenite, Olivine, Pigeonite) and olivine-rich Apollo 17 (A-17) Type C basalt, 74275, have also been analyzed. As a complement to the chemical analyses, crystal size distributions (CSDs) were determined for approximately half of the samples investigated here (due to a small number of olivine crystals that did not produce statistically meaningful CSDs on half of the samples), and confirm that although similar, the basalts and impact melts are texturally distinct. Olivines from A-14 impact melts have the highest average forsterite contents (average Fo ∼0.82) and generally the lowest average Co (37ppm) and Mn (1544ppm) abundances, thus chemically distinguishing them from the pristine basalts. In addition, chemical compositions obtained for olivine from 14321,1486 are most likely representative of an impact melt and thus contradict its previous classification as a high-Al basalt (Neal et al., 1988); olivine from, 1486 have similar average forsterite (average Fo ∼0.82) and Ti/V-ratio to the OVs. Furthermore, on the basis of their chemical compositions, olivines have been identified within the impact melts that are likely inherited from basalts; these olivines are chemically distinct from the rest of the impact melt olivine population with lower forsterite (0.67–0.80) and low Ti/V (∼10), which are similar to olivine compositions from the A-14 high-Al basalts. In addition to distinguishing between sample types from A-14, olivine compositions can also be used to distinguish between pristine mare basalts from various missions. Olivine within the selected samples from the individual A-12 basalt suites can also be distinguished chemically from one another using the Ti/V ratio, where Olivine suite basalts have Ti/V <3 and Ilmenite suite basalts have Ti/V >3.5. The results indicate that combined use of CSDs and chemical analyses of olivine can be used to reliably distinguish between (1) impact melts and pristine Apollo 14 basalts, (2) basalts from different landing sites, and (3) individual basalt suites from a single site.

Isotopic analysis of antimony using multi-collector ICP-mass spectrometry for provenance determination of Roman glass

Based on promising results obtained in earlier work on antimony ores, we have investigated the use of natural variation in the isotopic composition of Sb as determined using multi-collector ICP-mass spectrometry (MC-ICP-MS) for provenancing Roman glasses. In antiquity, Sb was used either as a decolourizer or as an opacifier and thus, colourless and opaque coloured glasses from different regions and periods were selected for investigation. Both, the sample digestion and isolation of Sb preceeding isotopic analysis via MC-ICP-MS have been optimized and validated for this type of materials. For this purpose, NIST SRM 610 glass reference material and an in-house standard were employed. Isotope ratio determinations were carried out by MC-ICP-MS, relying on In as an internal standard for correction for instrumental mass discrimination. The merits of external calibration in a sample-standard bracketing approach and the so-called “revised Russell's law” for mass bias correction were compared, with the latter providing higher precision and better reproducibility. The 123Sb/121Sb isotope ratio in glass could be determined with a reproducibility (or external precision) of ca. 0.4ε, while in Roman colourless and Hellenistic opaque glass samples, a variation of 3 to 4ε units was found. The results seem to suggest the use of similar Sb sources for both types of glasses, and the existence of at least two different Sb sources for glass production in the Roman era.

Im flüßgen Element hin und wieder schweifen : Development and Return in Goethe’s Poetry and Hegel’s Philosophy

After an exchange of letters early in 1821, Goethe was so pleased by sensitivity of Hegel's reflections on a concept central to his own thought that he sent Hegel a gift of an opaque wine glass, with dedication:Dem Absolutenempfiehlt sichschonstenszu freundlicher AufnahmeUrphanomen.1This vignette, tongue-in-cheek though it is, points to an enduring meeting of minds between two thinkers, which can be detected in most surprising places. The parallels between Goethe's West-ostlicher Divan (1819) and fundamentals of Hegel's thought have never been remarked upon, even though they are remarkable. My purpose here is to draw out those similarities, to listen beyond apparent differences in voices of these two thinkers to internal resonance between their ideas.Goethe and Hegel corresponded intermittently for some two decades, and there was significant mutual respect, even admiration, between them. Hegel was outspoken in his defense of Goethe's Farbenlehre, which had been harshly received, and he was deeply influenced by Goethe's theory of morphology.2 Goethe, for his part, valued Hegel's unique mind, and commented on more than one occasion on Hegel's sensitivity to his own ideas.3 Of course, they remained profoundly different thinkers. It goes without saying that Goethe did not share Hegel's conception of Geist, and that he did not seek, as Hegel did, to develop an all-encompassing philosophical system. Moreover, in his drafted letter to Seebeck of November 28, 1812, Goethe expresses disquiet at concept of negation Hegel deploys in his account of natural development in Vorwort to his Phanomenologie des Geistes (not, as Goethe calls it in letter, Logik, which at time was unpublished): Die Knospe verschwindet in dem Hervorbrechen der Blute, und man konnte sagen, das jene von dieser widerlegt wird .. 7T28-31).4 Although Goethe retracted his initial scathing comments almost immediately (FA 7:131), and declared himself to be more satisfied once Seebeck had explained context of remark to him (FA 7:151), negation was one aspect of Hegel's system that remained foreign to him.5 Yet other moments in Phanomenologie bear a much stronger relation to Goethe's way of thinking. The similarities between their conceptions of development-in Hegel's case, of Geist, in Goethe's, of self and poetry-are particularly striking, and demand to be explored further. My concern here is not with narrow question of who influenced whom: indeed, such an approach would hardly allow comparison room to breathe. Rather, parallels can be attributed partly to philosophical tradition (especially thought of Leibniz and Spinoza) in which both were steeped, and partly to currents of thought, known collectively as Idealism, which were swirling around both.Goethe and Hegel share an understanding of being as becoming, as Werden-, for both, process of becoming perfect or complete is as significant as goal; and it is interdependence of these two, of process and telos,that constitutes life.6 In preface to his Phanomenologie, Hegel lays down fundamental principles of life of Geist: [Das Wahre] ist das Werden seiner selbst, der Kreis, der sein Ende als seinen Zweck voraussetzt und zum Anfange hat und nur durch die Ausfuhrung und sein Ende wirklich ist (Werke 3:23)For Hegel, then, end state of Geist (its truth), goal of its development, is always implicit in its beginning; many forms that it takes are all part of a process of it becoming more itself. Old and new, beginning and ending, are not separate, static poles, but are intimately bound up in one another. That which is old is also, in some ways, most new, in sense that it is originary, embryonic, and always present in newer forms that succeed it. Brady Bowman observes that the peculiar coincidence of succession and simultaneity, of genesis and structure, is a striking feature shared by [the] methods [of both Goethe and Hegel];7 and in Divan poem Unbegrenzt (FA 3. …

Owners fail to influence the choices of dogs in a two-choice, visual pointing task

Experiments that use human pointing gestures in two-way object choice tests are popular for studying visual communication and referential understanding but results may be influenced by involuntary cues from handlers or experimenters (i.e., ‘Clever Hans Effects’). In this paper we investigated whether such cues from a dog’s owner affected performance of dogs during momentary distal pointing trials. Dogs were tested in four groups. In the ‘Blindfolded Owner’ group, the owners did not see the experimenter’s pointing gestures because they wore opaque glasses. In the ‘Passive Clever Hans’ group, owners were told before the test that if their dogs performed without error, they would receive a gift and their dog would be recorded in the ‘smartest dogs registry’. In the ‘Active Clever Hans’ group, owners were instructed to help their dogs to the correct side by pushing them gently in the correct direction. The fourth group served as a control and owners did not wear a blindfold or receive any specific information. We found no influence of cues from the owners in any of the experimental groups. In contrast to studies based on olfactory cues, this suggests that momentary pointing gestures from a human experimenter can be a reliable communicative cue for adult companion dogs, even when dog owners are present and provide additional voluntary or involuntary cues. We suggest that for short-term studies of visual communication, where individual dogs have little opportunity to learn their owners’ cues in the experimental context, the presence of owners may not necessarily distort results.

Structural characteristics and dielectric response of some zinc tellurite glasses and glass ceramics

The structural characteristics of a system of optically transparent xZnO(1−x)TeO2 glasses, with x=0.1, 0.2, 0.3 and 0.4 (mole fraction) obtained by conventional melt-quenching technique and heat treated glass ceramics were studied with X-ray diffraction (XRD), micro-Raman and infrared spectroscopy (FTIR) techniques. The dielectric spectroscopy measurements were performed over the temperature range of 100K to 360K and frequency range from 40Hz to 2MHz.The as-prepared transparent yellow glasses were found to turn into opaque (white) glass ceramics when heat treated at three temperatures (350°C, 440°C and 505°C); the temperatures were chosen on the basis of DTA data of the base glasses. The XRD patterns of the glasses treated above 350°C show the formation of crystalline phases of Zn2Te3O8, Zn(TeO3) and TeO2. The FTIR and the Raman spectra, obtained using an excitation line of 532nm, are in agreement with the structural changes inferred from the X-ray data. Dielectric relaxation phenomena were observed in these samples and correlated with the heat treatment parameters.

Polymerization efficiency through translucent and opaque fiber posts and bonding to root dentin

PurposeTo investigate the polymerization efficiency through translucent and opaque glass fiber posts and the bond strength of a self-adhesive resin to root dentin. MethodsTranslucent and opaque silanated conical posts, identical in length, diameter and shape (n=8), were cemented to incisor bovine roots using RelyX Unicem Clicker. Photoactivation was performed only through the posts. The roots were transversally sectioned (cervical, middle and apical thirds) and the push-out test was carried out. Data were analyzed using two-way ANOVA and Fisher's LSD method (5%). Failure modes were classified under magnification. An elastomer mold of a bovine incisor root was filled with flowable composite and the posts inserted into the mold. After photoactivation through the post and removal of unpolymerized material, the polymerization efficiency was estimated by percentage of mass gain (n=5). Data were analyzed using t-test (5%). ResultsThe bond strength of the translucent post was higher than the opaque post for all root thirds. For both posts the bond strength at the cervical third was higher than at the middle and apical thirds. A predominance of adhesive failures was detected for all conditions. Mixed failures were more frequently observed for the opaque post. Almost all the composite polymerized and bonded to the extension of the translucent post, whereas polymerization of the composite was restricted to the cervical area of the opaque post. ConclusionsThe use of translucent post may positively influence the polymerization efficiency and bond strength of resin cement to intraradicular dentin.

Investigation of matrix effects in 193 nm laser ablation-inductively coupled plasma-mass spectrometry analysis using reference glasses of different transparencies

The degree of transparency of glasses, which depends on the Fe content, may influence the ablation behavior during laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis. To test possible matrix effects when using a 193nm Nd:YAG laser, we have analyzed transparent and opaque NIST, BAM and USGS reference glasses. These reference materials are ideal for such investigations, because they are well characterized, most elements are homogeneously distributed at the micrometer scale, and their Fe content varies over a very large range, from 16 to 130,000μgg−1. Our measurements show that the fractionation factors of refractory and volatile lithophile elements, such as Sr, Ba, and Rb, are 1.00±0.03 and independent of the degree of transparency. However, for volatile chalcophile/siderophile elements (e.g., Zn and Pb) the fractionation factors vary significantly between 0.7 and 1, depending on the spot sizes and the transparency of the material. Mass-load-induced matrix effects may also influence the accuracy of LA-ICP-MS analysis. They are less than 2% for the lithophile and up to 10% for volatile chalcophile/siderophile elements when the mass load varies by a factor 2.4. Relative sensitivity factors used for calibration of lithophile elements agree within uncertainty limits for transparent and opaque glasses when using a 193nm laser. Even for volatile/chalcophile elements they differ only by 5–10%.The reliability of the LA-ICP-MS analyses is demonstrated by presenting concentration data of 27 trace elements in the NIST, BAM and USGS reference glasses using NIST SRM 612 for calibration, where highly accurate reference values are available. For trace element concentrations in the range between 1 and 500μgg−1, the reproducibility and the uncertainties at the 95% confidence level of the measurements vary between 1–4%, and 7–10%, respectively.

Study of an archeological opaque red glass bead from China by XRD, XRF, and XANES

As a kind of rare archeological founding in China, red decorative beads (300–400 ad) were discovered in Leijiaping, Badong County, Hubei, China. For the first time, this paper reports an advanced structural analysis of glass beads using micro synchrotron X‐ray near‐edge absorption spectroscopy. The results show that in spite of being opaque, the red bead is made of glass containing two forms of copper atoms, including 0+ and 1+. In combination with X‐ray diffraction results, it is advised that the mechanism of red coloration mainly comes from metallic copper. This paper indicates that micro synchrotron X‐ray near‐edge absorption spectroscopy is an outstanding and advanced technology to study ancient glass objects with nondestructive mode. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Pre-Roman glass from Mozia (Sicily-Italy): the first archaeometrical data

This study present the results of an archaeometrical investigation performed on a series of opaque pre-Roman glass (vessels and ornaments) dated from the 6th to 4th century BC coming from Sicily. Sixteen core formed vessels, twelve beads, three pendants and one spindle-whorl recovered in the Phoenician-Punic sites of Mozia and Birgi were analysed thought a micro destructive approach. The complete chemical analyses and X-Ray diffraction analyses were performed on small fragments of glass. The aims of this work are: 1) to obtain a chemical characterization of these samples in order to understand the raw materials employed for their production; 2) to obtain information regarding the opacifying phases dispersed in the glass; 3) to make a comparison with the results recently obtained on coeval and similar finds recovered in other cultural context, in particular in Northern Italian Etruscan contexts in order to understand whether they could belong to the same Greek-Eastern production.The chemical data of these samples confirm they are silica soda lime glass produced with natron. The opaque decorations of the samples were done by using Sb based opacifiers. The major and minor analyses of the majority of the samples seem to suggest a common origin with the coeval material found in Northern Italian context. On the contrary, for some artifacts, in particular the pendants, a Phoenician-Punic origin is supposed.

The palaeo-Christian glass mosaic of St. Prosdocimus (Padova, Italy): archaeometric characterisation of tesserae with antimony- or phosphorus-based opacifiers

The present paper reports the results of archaeometric characterisation of the opaque tesserae, intentionally coloured with antimony- or phosphorus-based opacifiers, coming from one of the two only palaeo-Christian glass mosaics known in the Veneto region (Italy), i.e., the mosaic which decorated the votive chapel of St. Prosdocimus in Padova. In particular, 55 tesserae belonging to glass types “White”, “Blue”, “Yellow”, “Green” and “Brown” are examined here. The multi-methodological approach (SEM-EDS, EMPA, XRPD, imaging spectroscopy coupled, in some cases, with XAS) gave valuable insights into the complexities of palaeo-Christian glass mosaic production technologies. Two main groups are identified, one characterised by glassy matrixes and opacifiers (calcium or lead antimonate) typical of the Roman period and comprising all “White”, “Blue”, and “Yellow” tesserae and some “Green” ones, and the other characterised by glassy matrixes and an opacifier (calcium phosphate) typical of the 6th century AD, composed of “Green” and “Brown” tesserae. This suggests that, during that century there was a gradual change from older to “new” production technologies: although new opacifiers such as calcium phosphate started to be used, the frequent use of antimony-based ones (43/55 samples) supports the hypothesis that their systematic use was extended until the 6th century, although re-using old tesserae cannot be completely excluded. In addition, comparisons with compositional groups already identified in the “gold” tesserae of the same mosaic and tesserae from Ravenna demonstrate that both the same “base compositions” of the glass were used to produce transparent and opaque glass. This evidence, coupled with the results of the historical-artistic study, suggests technological connections between Padova and Ravenna, the capital of Byzantine mosaics in Italy. Micro-structural observations and chemical analyses of the Paduan antimony-based opacified glass demonstrate that different processes and raw materials were used in their production. Both in situ and ex situ crystallisation can be identified for calcium and lead antimonate in Paduan tesserae, whereas the production of tesserae opacified with calcium phosphate generally appears to be highly standardised. Although the opacifiers used in the Paduan tesserae support technological transitions, the colouring elements identified here, i.e., iron and manganese for white, yellow, brown and some green tesserae, cobalt for blue, and copper for blue and green, suggest continuity, because their use is widely testified in the production of both transparent and opaque glass artefacts dating from the Bronze Age until Medieval times, from whichever archaeological site the samples come. Peculiar relationships among the oxidation states of colouring elements, their contents in the glassy matrix, the types of opacifiers used, and the final colour of tesserae were identified. In addition, the correlations of cobalt and/or copper with other elements, together with identification of relics of colouring and “metallic” droplets, allow us to speculate on possible sources and production technologies. Lastly, identification of newly formed crystalline inclusions in tesserae also yields information on kiln temperatures, which ranged between 900 and 1150 °C, a range easily reached in the furnaces of the 6th century AD.