Calcium Antimonate Research Articles

PXRF, μ-XRF, Vacuum μ-XRF, and EPMA Analysis of Email Champlevé Objects Present in Belgian Museums

The enamel of 20 Email Champlevé objects dating between the 12th and 19th centuries was investigated by means of microscopic and portable X-ray fluorescence analysis (μ-XRF and PXRF). Seven of these objects were microsampled and the fragments were analyzed with electron probe microanalysis (EPMA) and vacuum μ-XRF to obtain quantitative data about the composition of the glass used to produce these enameled objects. As a result of the evolution of the raw materials employed to produce the base glass, three different compositional groups could be discriminated. The first group consisted of soda-lime-silica glass with a sodium source of mineral origin (with low K content) that was opacified by addition of calcium antimonate crystals. This type of glass was only used in objects made in the 12th century. Email Champlevé objects from the beginning of the 13th century onward were enameled with soda-lime-silica glass with a sodium source of vegetal origin. This type of glass, which has a higher potassium content, was opacified with SnO2 crystals. The glass used for 19th century Email Champlevé artifacts was produced with synthetic and purified components resulting in a different chemical composition compared to the other groups. Although the four analytical techniques employed in this study have their own specific characteristics, they were all found to be suitable for classifying the objects into the different chronological categories.

A Raman spectroscopic study of glass trade beads excavated at Mapungubwe hill and K2, two archaeological sites in southern Africa, raises questions about the last occupation date of the hill

Thousands of glass trade beads were excavated over a 75 year period on Mapungubwe Hill and at K2, two archaeological sites in the Limpopo valley, South Africa. An assemblage of 175 beads that appeared to be different in shape, size and colour (red, yellow, green, blue, white, black, pink, plum) was studied with Raman scattering. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe–S “amber” and a spinel) have been identified. Pigment identification allows the recognition of specific productions and indicated that many of the pigments colouring the beads excavated on Mapungubwe hill were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record, some dating from the 19th century. This date is in agreement with the last occupation date for the hill suggested by the earlier excavators and raises questions about the revision of this date to 1290 AD by archaeologists in the 1970’s.

The glass of Nogara (Verona): a “window” on production technology of mid-Medieval times in Northern Italy

The site of Nogara (province of Verona, Italy) provides valuable insights into the complexities of the glass industry in mid-Medieval times, due to its timing, which ranges mainly between the 10th and 11th centuries AD, and to the great quantity of glass findings, mainly tableware. In the present paper, the combination of archaeological, chemical and textural data allows us to identify production technologies in a time-interval perceived to be a period of technological transition for glass. In particular, the frequent occurrence of recycled natron glass and only a few glass samples made with soda plant ash indicate that recycling of earlier glass was common in inland Northern Italy in the 10th–11th centuries AD. In addition, blue and reticello decorations were obtained by recycling earlier glass mosaic tesserae, as shown by much Co, Cu, Sn, Sb and Pb and the presence of crystallised calcium antimonates. A few glass samples with chemical compositions intermediate between natron and soda plant ash glass were also identified, suggesting a gradual change in glass composition from natron-based towards soda ash-based production technology, which prevailed in the 13th-14th centuries. In conclusion, the difficulty in describing mid-Medieval glass as a well-defined entity, due to the great propensity for recycling earlier glass samples which causes variability in chemical compositions, particularly those of trace elements, is clearly documented here. In any case, this paper contributes to a new type of chrono-typological scanning and to more detailed knowledge of glass production technology during mid-Medieval times in Northern Italy, little found in the literature until now.

Stability of pyrochlores in alkaline matrices: Solubility of calcium antimonate

The stability of pyrochlores as a function of solution composition is relevant in the context of hazardous waste immobilisation as this mineral family comprises minerals that can control actinide solubility in ceramic formulations as well as romeites or calcium antimonates that possibly control the solubility of Sb in cement pastes. However, to date, no thermodynamic model exists that can be used for long-term risk assessment of pyrochlores as stabilising minerals. In this work synthetic romeites were precipitated at pH 6.5 and pH 12 and at varying molar Ca:Sb ratio and analysed by XRD and Rietveld refinement which showed that, like naturally occurring romeites, synthesized romeites have a Ca1+xSb2O6OH2−2x structure with less vacancies and a higher Ca-content as pH and Ca-availability were higher during synthesis. These romeites dissolve incongruently with preferential Ca leaching and antimonate is less soluble from romeites synthesized in alkaline conditions. Batch extractions of romeite in equilibrium with increasing Ca(NO3)2 additions up to 1 mol L−1 showed a minimum equilibrium Sb concentration at [Ca] = 0.01 mol L−1 that could only be explained by assuming the formation of a CaSb(OH)6+ complex. Increasing the Ca concentration in romeite suspensions also resulted in a pH decline in the equilibrium solution, which may be explained by the increasing concomitant uptake of Ca2+ and OH− in the romeite structure as a function of increasing Ca(NO3)2 additions. Thermodynamic modelling supported these assumptions that may explain the incongruent dissolution behaviour of romeite, but the fitting of two equilibrium constants was required. Although the validity of these constants needs more experimental confirmation, this study suggests that despite possible CaSb(OH)6+ formation, the solubility of Ca antimonate in alkaline conditions can be responsible for lower equilibrium Sb concentrations than previously assumed.

The Mediterranean Group II: analyses of vessels from Etruscan contexts in northern Italy

A large number of Mediterranean Group vessels were recovered at the Etruscan site of Spina in northern Italy and dated from the 6th to the 3rd century BC. In this work a number of vessels belonging to the so-called “Group II” were analysed. The samples are mainly Alabastra, Oinochoai, Amphoriskoi, and Hydriai, in general opaque and deeply coloured. The aims of this study are: 1) to characterize these samples since there is a lack of data in literature regarding Mediterranean Group II; and 2) to compare the data obtained with that of glass for previous centuries (Mediterranean Group I) recovered at the same site in order to establish whether they could have the same origin. The chemical analyses of major and minor elements were carried out by electron microprobe and the nature of the opacifying and colouring agents was determined by X-ray diffraction. The sample set is relatively homogeneous and most of the samples can be classified as Low Magnesium Glass produced with natron and a calcareous silicatic sand. The XRD analyses proved the use of lead antimonates in the manufacture of yellow decorations and of calcium antimonates in the white and light blue decorations. The consistency of the chemical compositions of Mediterranean Groups I and II samples makes it possible to hypothesize a common origin.

Sword and Dagger Pommels Associated with the Crusades, Part II: A Technical Study

The article discusses the results of a technical study of a collection of medieval sword and dagger pommels owned by the Metropolitan Museum of Art in New York City, with particular focus given to the probable use of the lost-wax technique to create them and the conclusion that they were most likely created in Europe due to the presence of Champleve enameling. A brief overview of medieval metalwork is presented, and the pommels and their creation are described in detail. The association of the pommels with the crusades is also commented on.

Cellular localisation of calcium ions during potato hypersensitive response to Potato virus Y

Ca2+ is one of the most universal and versatile signalling molecules and is involved in almost every aspect of cellular processes. Accumulating evidence suggests that Ca2+ serves as a messenger in many growth and developmental processes and in plant responses to biotic and abiotic stresses. Numerous signals have been shown to induce transient elevation of cytoplasmic [Ca2+]cyt in plants. The calcium free ions were detected cytochemically in Solanum tuberosum cv. Rywal tissues as a hypersensitive response (HR) from 10h to 5 days after a Potato virus Y (PVY) infection. Calcium was detected in vivo by its reaction with Alizarin S Red, producing an intense red staining in contact with calcium free ions. Calcium was found in the necrotic area of the epidermal and mesophyll cells 3 days after the PVY infection (when morphological symptoms on potato leaves appeared). Calcium ions were detected cytochemically in HR also by its reaction with potassium pyroantimonate. Inoculation with PVYNTN and also PVYN Wi induced a rapid hypersensitive response during which highly localised increased accumulation of electron-dense deposits of calcium pyroantimonate were detected. Calcium deposition was observed in necrotic and non-necrotic areas, starting from 10h after PVY infection. The deposits were present along ER cisternae, chloroplasts and mitochondria envelopes connected with PVY particles. The precipitates of calcium antimonate were detected near the nuclear envelope, inside karyolymph and along tracheary elements, especially when virus particles were present inside.

New insight on the in situ crystallization of calcium antimonate opacified glass during the Roman period

Glass is usually opacified by small crystalline particles, called opacifiers, dispersed in the translucent vitreous matrix. To understand the glassmaking conditions used to produce calcium antimonate opacified glass, the in situ crystallization process has been studied through synthetic glasses made in the laboratory. The effects of the nature and the concentration of the antimony source, the temperature and the duration of heat-treatments on the calcium antimonates crystallization have been tested. The physico-chemical characteristics of these glasses were compared to Roman mosaic tesserae from Aquilea and Rome (1st cent. B.C.–6th cent. A.D.). We show that the glass composition (EDX), the microstructure (SEM-BSE, imaging treatment), the oxidation state of antimony in the vitreous matrices (μ-XANES) and the proportion of the crystalline phases (XRD with Rietveld refinement) are suitable parameters to assess glassmaking conditions used in ancient times. We demonstrate that opaque Roman glasses were obtained by in situ crystallization, probably using roasted stibnite Sb2O4 and by doing heat-treatment between 1 or 2 days.

Raman spectroscopic study of the antimonate mineral roméite

Raman spectroscopy has been sued to study the antimony containing mineral roméite Ca 2Sb 2O 6(OH,F,O) from three different origins. Roméite is a calcium antimonate mineral of the pyrochlore group. An intense Raman band at ∼518 cm −1 for roméite is assigned to the SbO ν 1 symmetric stretching mode and the band at 466 cm −1 to the SbO ν 3 antisymmetric stretching mode. The Raman band at 303 cm −1 is attributed to the OSbO bending mode. Some variation in band positions is observed and is attributed to the variation in composition between the three mineral samples.

The first archaeometric data on polychrome Iron Age glass from sites located in northern Italy

A large sample set of transparent and opaque glass artefacts recovered from Etruscan contexts in northern Italy (Bologna and Spina (FE) necropoleis) and dated to a period between the 6th and 4th century BC are analysed in this paper. Samples of highly decorated beads, spindle whorls and vessels of the ‘Mediterranean Group I’ (Alabastron, Oinochoes, Amphoriskos) were selected in order to determine whether these different glass artefacts were produced at the same manufacturing site. While the vessels almost certainly originate from Greece, the beads could derive from a more ancient local production ascertained at the site of Frattesina (Rovigo, Italy) and dated to the Bronze Age. The aims of this study are: (i) to characterise a set of Iron Age glass artefacts, thus providing new quantitative chemical data; and (ii) to identify possible differences between finds recovered from different localities and between glass vessels and beads, in order to establish whether different manufactures were active contemporaneously. The chemical analyses of major and minor elements were performed with an electron microprobe. The nature of the opacifying and colouring agents was determined by X-ray diffraction. The sample set is relatively homogeneous and most of the samples can be classified as low magnesium glass. The yellow opaque decorations are rich in Pb and Sb, while only Sb is present in the white and light blue samples. The XRD analyses confirmed the presence of lead antimonates in the yellow decorations and of calcium antimonates in the white and light blue decorations.

Synthesis of calcium antimonate nano-crystals by the 18th dynasty Egyptian glassmakers

During the 18th Egyptian dynasty (1570–1292 B.C.), opaque white, blue and turquoise glasses were opacified by calcium antimonate crystals dispersed in a vitreous matrix. The technological processes as well as the antimony sources used to manufacture these crystals remain unknown. Our results shed a new light on glassmaking history: contrary to what was thought, we demonstrate that Egyptian glassmakers did not use in situ crystallization but first synthesized calcium antimonate opacifiers, which do not exist in nature, and then added them to a glass. Furthermore, using transmission electron microscopy (TEM) for the first time in the study of Egyptian opaque glasses, we show that these opacifiers were nano-crystals. Prior to this research, such a process for glassmaking has not been suggested for any kind of ancient opaque glass production. Studying various preparation methods for calcium antimonate, we propose that Egyptian craftsmen could have produced Ca2Sb2O7 by using mixtures of Sb2O3 or Sb2O5 with calcium carbonates (atomic ratio Sb/Ca=1) heat treated between 1000 and 1100°C. We developed an original strategy focused on the investigation of the crystals and the vitreous matrices using an appropriate suite of high-sensitivity and high-resolution micro- and nano-analytical techniques (scanning electron microscopy (SEM), X-ray diffraction (XRD), TEM). Synchrotron-based micro X-ray absorption near edge spectroscopy (μ-XANES) proved to be very well suited to the selective measure of the antimony oxidation state in the vitreous matrix. This work is the starting point for a complete reassessment not only of ancient Egyptian glass studies but more generally of high-temperature technologies used throughout antiquity.

A non-invasive study of Roman Age mosaic glass tesserae by means of Raman spectroscopy

Ancient mosaic tesserae are a range of materials of very varied and complex nature, including pottery, stone and glass. Raman spectroscopy is a powerful tool for the analysis of all these kinds of materials. In the particular case of glasses, this technique can be used both for a study of surface weathering and for the characterization of bulk structure, but it has not yet been extensively used for the characterization of mosaic glass tesserae. We carried out Raman analyses on a set of Roman and Late Antiquity period mosaic glass samples, which allowed a good characterization of both the glass matrix and the crystalline inclusions. All the samples show the typical Raman signatures of soda-lime-silicate glasses. Several crystalline phases were also identified, being relics of raw materials used during the glass manufacturing process, such as quartz and feldspars, or linked to the glass color/opacification, such as bindheimite and cuprite. The analyses also led to the identification in some blue, turquoise and green tesserae of calcium antimonate, whose Raman signature has only recently been recognized in the scientific literature on mosaic glasses. Some emphasis is given to the analysis of red lead-containing tesserae, colored with Cu + ions or even Cu 0 (or Au 0) metal nanoparticles. Samples with peculiar compositions, as well as “modern” (and restoration) samples, could quite easily be distinguished from the ancient ones by their Raman spectra.

Chemical composition and colouring agents of Roman mosaic and millefiori glass, studied by electron microprobe analysis and Raman microspectroscopy

About 100 fragments of Roman mosaic and millefiori glass were stylistically attributed to a Hellenistic type, a Ptolemaic and Romano-Egyptian period type and an early imperial period type. Twelve representative fragments were studied by electron microprobe analysis and Raman microspectroscopy. Eleven of them display a Na-pronounced recipe with low K, Mg and P contents, typical for the Roman period. Minor differences in composition are unsystematic, not reflecting the stylistic classification. Ionic colouring agents are Mn3+ for violet, Cu2+ for light blue, Co2+ for deep blue and Fe3+ for brown translucent colours. Calcium antimonates, lead antimonate and cuprite are the colourants responsible for white, yellow and red colours, respectively, and additionally serve as opacifiers. Mixing of ionic colouring agents and opacifying colourants led to a more differentiated palette of colours. Pb was used as yellow colouring agent, as a flux material and as a stabiliser for the colourant crystals. The remaining fragment consisting of a K-pronounced but still Na-bearing glass matrix was most likely produced during the Middle Ages or later.

The dynamic changing of Ca 2+ cellular localization in maize leaflets under drought stress

Maize cultivar zhengdan958 was selected as materials. The sub-cellular distribution of soluble calcium at different phases was shown by the potassium-pyroantinonate-precipitation method and transmission electron microscopy. The results showed that the deposits of calcium antimonate as the indicator for Ca 2+ localization were mainly concentrated within the vacuoles and intercellular spaces without PEG treatment. Firstly, when the leaf was treated with PEG, the Ca 2+ level increased remarkably in the cytoplasm, but considerably decreased in vacuoles and intercellular gaps. Meanwhile, the level of Ca 2+ also increased in chloroplast and nucleus. When the treatment continued, the level of Ca 2+ in chloroplasts and nucleus continued to increase and some cells and chloroplasts finally disintegrated, showing that there is a relationship between the distribution of Ca 2+ and the super-microstructure of cells. Ca 2+ plays a role in the plant drought resistance. The changes of cytosolic Ca 2+ localization in cells treated by ABA, EGTA, Verapamil and TFP were investigated too. The increase of cytosolic calcium induced by ABA was mainly caused by calcium influx. Calmodulin participated in ABA signal transduction, which was indicated by the variation of cytosolic Ca 2+/CaM concentration change induced by ABA. The above results provided a direct evidence for calcium ion as an important signal at the experimental cellular level. To cite this article: Y.Y. Ma et al., C. R. Biologies 332 (2009).

Effects of Exterior Abscisic Acid on Calcium Distribution of Mesophyll Cells and Calcium Concentration of Guard Cells in Maize Seedlings

In this study, the direct effects of exterior abscisic acid (ABA) on both calcium distribution of mesophyll cells and cytosolic calcium concentration of guard cells were examined. The distribution of Ca2+ localization were observed with calcium antimonate precipitate-electromicroscopic-cyto-chemical methods after treated with ABA and pretreated with ethylene glycol-bis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA), verapamil (Vp), and trifluoperazine (TFP). The laser scanning confocal microscopy was used to measure the cytosolic calcium concentrations of guard cells under different treatments. The results showed that the cytosolic Ca2+ concentration of mesophyll cells was induced to increase by ABA, but to decrease in both outside cell and the vacuoles within 10 min after treatments. The cytosolic calcium concentration of guard cells was increased gradually with the lag in treatment time. However, both EGTA and TFP could inverse those effects, indicating that the increase of cytosolic calcium induced by exterior ABA was mainly caused by calcium influx. The results also showed that calmodulin could influence both the calcium distribution of mesophyll cells and calcium concentration of guard cells. It shows that calmodulin participates in the process of ABA signal transduction, but the mechanism is not known as yet. The changes both calcium distribution of mesophyll cells and calcium concentration of guard cells further proved that the variations of cytosolic Ca2+ concentration induced by ABA were involved in the stomatal movements of maize seedlings.

Polychrome glass from Etruscan sites: first non-destructive characterization with synchrotron μ-XRF, μ-XANES and XRPD

This work is devoted to the characterization of a suite of very rare, highly decorated and coloured glass vessels and beads from the VII to the IV century BC. The most serious difficulty in developing this study was that any sampling – even micro-sampling – was absolutely forbidden. As a consequence, the mineralogical and chemical nature of chromophores and opacifiers present in these Iron Age finds were identified by means of the following synchrotron-based, strictly non-destructive, techniques: micro X-ray fluorescence (μ-XRF), Fe K-edge micro X-ray absorption near edge spectroscopy (μ-XANES) and X-ray powder diffraction (XRPD). The μ-XRF mapping evidenced high levels of Pb and Sb in the yellow decorations and the presence of only Sb in the white and light-blue ones. Purple and black glass show high amounts of Mn and Fe, respectively. The XRPD analyses confirmed the presence of lead and calcium antimonates in yellow, turquoise and white decorations. Fe K-edge μ-XANES spectra were collected in different coloured parts of the finds, thus enabling the mapping of the oxidation state of these elements across the samples. In most of the samples iron is present in the reduced form Fe2+ in the bulk glass of the vessels, and in the oxidized form Fe3+ in the decorations, indicating that these glass artefacts were produced in at least two distinct processing steps under different furnace conditions.

Antimony leaching from uncarbonated and carbonated MSWI bottom ash

The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by the leaching of antimony (Sb). Therefore, treatment methodologies need to be developed. The pH-dependent leaching behaviour of this oxyanion-forming element in fresh and weathered bottom ash is, however, not understood. Sb leaching was investigated in a wide range of both pH and extent of carbonation. Sb came close to equilibrium with calcium antimonate (Ca[Sb(OH) 6] 2) at acid and neutral pH. Therefore, adsorption experiments with synthetic calcite (CaCO 3), ettringite (Ca 6Al 2(SO 4) 3(OH) 12·26H 2O), gypsum (CaSO 4·2H 2O), and portlandite (Ca(OH) 2) and adsorption modelling to hydrous ferric oxides (HFO) and amorphous aluminium minerals (AAM) were conducted to investigate which minerals decrease Sb leaching below equilibrium with calcium antimonate. At pH > 12, calcium antimonate comes into solution due to portlandite formation, but the subsequent increase in Sb leaching is reduced due to strong interaction of Sb with portlandite and ettringite. Ettringite appears to be an important host mineral for Sb at the natural pH of mildly weathered bottom ash (11.8) because a minimum in leaching is observed. When pH is decreased below 10.5, ettringite dissolves and Sb comes into solution, approaching equilibrium with calcium antimonate near pH 9. Gypsum showed no affinity for Sb. The interaction of calcite with Sb was not clear. Adsorption modelling suggested that HFO, rather than AAM, control Sb leaching when pH < 9. During carbonation, Sb leaching first increased, most likely due to dissolution of ettringite. Then, Sb leaching decreased, since the pH became low enough to allow sorption by HFO.

Archaeometric analyses of game counters from Pompeii

Abstract Among the glass finds of the Pompeii excavations, numerous objects of opaque and transparent glassy material of different colours were recovered and classified as game counters. The main aims of this work were to characterize these samples so as to identify the materials used as colorants and opacifying agents, and subsequently to deduce the technology used for their production. The results of the chemical and mineralogical analyses obtained for game counters were also compared with those obtained for transparent and opaque glass artefacts. The chemical analyses were carried out, using only 300 mg of sample, by both wavelength-dispersive electron microprobe and X-ray fluorescence analysis. The crystalline phases present in the opaque glass were identified using both an automatic X-ray powder diffractometer and a Gandolfi camera. Secondary and backscattered electron images were obtained to study the distribution and morphology of the opacifier particles, and qualitative chemical analyses were obtained with an energy-dispersive system. All the game counters analysed can be classified as silica-soda-lime glass. Two calcium antimonates (CaSb 2 O 6 and Ca 2 Sb 2 O 7 ) were identified in the opaque white, green and blue glass, and Pb 2 Sb 2 O 7 particles were detected in the opaque yellow glass. Particles of metallic copper were detected by both energy-dispersive system and X-ray powder diffraction. These results support the hypothesis that transparent game counters were obtained by remelting of fragments of common transparent artefacts. In contrast, opaque finds were probably produced using the glassy paste employed in the production of mosaic tesserae.

The use and origin of antimonate colorants in early Egyptian glass*

The origin of the colorants in Egyptian glass of the second millennium BC has been the subject of much research and debate. Several colorants including lead antimonate yellow and calcium antimonate white appear in the archaeological record apparently concurrently with the introduction of glass, and it is possible that their origins are in some way linked. This paper examines the use of the antimonate colorants and uses analytical and experimental techniques to deduce possible technologies of production. Trace element data derived from a pilot study by LA‐ICPMS gives additional indications of a possible source in the Caucasus for the antimony of these glasses.

Colourants and opacifiers in seventh and eighth century glass investigated by spectroscopic techniques.

Glass fragments dating from the seventh and eighth century AD were excavated in the Crypta Balbi in Rome. They were studied to detect agents involved in colour development and opacification. Reflectance spectra recorded on powdered samples revealed the contribution of Fe(II), Fe(III), Mn(III), Cu(II), and Co(II) ions in determining colour hues. The effect of the Mn/Fe atomic ratio on glass colour is discussed. It is apparent that medieval glassmakers in Italy could obtain a wide range of colours by exploiting the presence of iron and manganese as contaminants of sand and flux and controlling the amount of oxygen let into the furnace. X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray analysis were used to study opaque fragments. The presence of calcium antimonate was detected in white, blue, and blue-green fragments, and elemental copper was detected in a red glass.