Medieval Glass Research Articles

Neue Forschungen zu Glashandwerkern unter den Karolingern und ihren Nachfolgern ( 8. bis 10. Jahrhundert )

Abstract So far, the history of early Medieval glassmakers has mainly been derived from archaeological sources. Significant in this context was, more than half a century ago, the discovery of a new glass recipe, which began to spread in Europe from the ‘deepest’ early Middle Ages; the question of how this could develop is still subject of various discussions. A new contribution was published by Alexis Wilkin in 2019. According to this contribution, the early Medieval glass artisans owed the technological foundations of their new recipe to their collaboration with metal artisans. There is some clear evidence for this theory, but besides the technical innovation the social conditions of the artisans should not be forgotten. The glassmakers of the early Middle Ages were not free entrepreneurs, in the historical texts they are dependent on their landlords. This dependency, however, gives rise to a purely historical method of investigation: new finds of early Medieval glassworks manufactured according to the altered glass recipe can be assigned to the territories of specific landlords. This paper examines the extent to which family connections can be made visible in the passing on of glassmakers belonging to these families, perhaps also in the development of the new glass recipe.

Early medieval glass beads: witness to changes in central Europe – the case of Hostivice (Czech Republic)

Early medieval glass beads: witness to changes in central Europe – the case of Hostivice (Czech Republic)

The Medieval Glass Mosaic of S. Agnese fuori le mura in Rome: Multispectral Imaging for Preliminary Identification of Original Tesserae

The mosaic in the apse of the Church of S. Agnese fuori le mura in Rome represents one of the most important examples of the wall mosaics of the Roman Middle Ages. Although it is associated with Byzantine figurative culture, no scientific study has addressed this important piece of Italian art history. One factor that has probably limited and created difficulties for its analysis is the poor legibility of the original parts, which are compromised by heavy restorations affecting the gold background, the faces of the two male side figures, and the lower band of the mosaic. The present work describes how multispectral imaging provided significant guidance in the preliminary identification of possible original areas in this ancient wall mosaic. Through an interdisciplinary approach, the art historical background and historical graphic documentation of known restorations supported the use of multispectral imaging to recognize original parts. The initial results of the lab analyses (SEM-EDS and EMPA) of supposed original tesserae validated the hypothesis made a priori thanks to multispectral acquisition, opening up new application possibilities for use of this noninvasive technique in the preliminary in situ identification of original parts in restored glass wall mosaics.

Late antique and early medieval glass from the northern Venetian lagoon: New data from the archaeological site of Jesolo

Accurate microchemical characterisation was performed on a 4th-12th-century repertoire of coloured and colourless glass samples found in the archaeological excavation of Jesolo (ancient Equilus, northern Italy).The research aimed to improve the state-of-the-art knowledge of early medieval glass, through the characterisation of a stratigraphically very well-dated and homogeneous glass collection, further representing a unicum in the area of the western upper Adriatic.A representative sampleset of sixty-seven glass finds -including vessels, windows, tesserae and blocks of raw glass- was investigated by electron microprobe (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). All samples are classified as soda-lime-silica glass made of impure sands and natron. In most cases, glass colour is imparted by iron naturally present in the sands, often counteracted by varying levels of manganese. The collection also includes numerous Co– and Cu-coloured glass. Colourless glass is Mn-decoloured or, to a lesser extent, Mn/Sb-decoloured. The proportion between fresh and recycled glass is almost equal. The provenance investigation has established that while Levantine imports are numerically limited, most materials can be traced back to the Egyptian area. Among the twelve samples assigned to the Levantine area, both Jalame-type and Apollonia-type glass has been identified in an almost equal percentage. Among Egyptian glass, a consistent group of 22 samples has been straightforwardly assigned to the HIMTa and, to a lesser extent, HIMTb groups. Both group 2.1 and 3.2 are clearly attested in almost equal amounts but individually less frequent than HIMT.

A new perspective: the “WINDOWGLASSMED” project

Despite an apparent contraction of long-distant trade suggested by Pirenne,1 recent analytical studies suggest that glass was still traded to Europe from Egypt and the Levant where it was originally produced during the Early Medieval period.2 The overall picture that emerges from these data though is far from clear. In addition, there is no doubt that Early Medieval glass chemical composition has been heavily influenced by recycling and mixing recycling practices over the years,3 but at the same time, “contemporary” produced compositions (such as Levantine – Apollonia type, Foy 2, or plant ash) were also circulating at the time together with this highly recycled glass.4 There is no doubt therefore that our understanding of glass production is still partial to this day and that more works needs to be done, especially that e a broader range. The idea for the WINDOGLASSMED project stems from these premises. By analysing glass samples from different part of Western Europe for LA-ICP-MS and isotopic analysis (Sr and Nd), this project will be the first detailed multidisciplinary study focused on well-dated 7th–10th century to create a detailed, chronologically-resolved map of Early Medieval glass in Western Europe, reflecting both trade patterns and practices such as recycling.

On the Mystery of One Bead

The results of studying a biconical glass bead (14th century) found during excavations by the Institute of Archaeology, Russian Academy of Sciences, at the settlement of Rostislavl (urban district of Kolomna, Moscow oblast) in 2018 are presented. The studied bead specimen differs significantly from all beads traditionally found during excavations in this region. A combination of a complex of imaging methods (X-ray and neutron tomography), large-scale X-ray fluorescence mapping of the distribution of elements, scanning electron microscopy with energy-dispersive X-ray microanalysis, and phase analysis allow us to determine that the bead decoration was formed by several layers of materials of different composition. Quantitative information about the base composition and trace components is obtained by laser ablation inductively coupled plasma mass spectrometry. It is revealed that the bead was made by combining separate layers of the base and decorating material from glasses of two classes, lead silicate and potash lead. Both established glass classes bring it closer to the medieval glasses of Central Europe. In this case, such a combination of the composition and manufacturing technique of similar objects was first found on the territory of Old Russia.

The Comacchio Glass Workshop: A Late Seventh-Century Urban Production Site of the North Adriatic

This article is an in-depth review of the production structures found in Comacchio, dating to the middle of the seventh century ad, and the glass-ware, contextualizing both in the early medieval glass production processes. The final part of the article reflects on the role of Comacchio workshops in the Po Valley trading system and on the importance of these workshops for further developments in medieval glass production. For a general framework on the research project and on the excavation, see the article by Sauro Gelichi (in this volume).

Liturgical Constraints and Openness in Divine Address

While some constraints are necessary to the correct performance of liturgy, both the nature of liturgical language and its wider setting argue for openness. In the case of language, examples are drawn from scripture, formal liturgy and hymns to suggest that their power derives in part from their open, poetic character. The multivalent character of metaphor can help draw worshipers into dialogue with God. Because all metaphors are partial and inevitably fail at some point, elimination is not the best response to perceived inadequacies but the introduction of complementary images. Equally, instead of viewing the setting as a constraint, as in the Hindu concept of darshan it should be seen as an opportunity for God to speak through human artefact. While architecture is briefly addressed, the main focus is on stained glass. Pope Gregory’s “Bible for the illiterate” is quite wrong. Once the rules behind particular styles are appreciated, not only can its power to communicate divine presence be activated but also at times original reflections that go well beyond the merely “illustrative.” Examples range from medieval glass at Canterbury, Chartres and Sens to the work of modern artists such as Harry Clarke, Tom Denny, and Douglas Strachan.

Early medieval glass smoothers as a manifestation of the spread of Christianity in Mainland Europe

Abstract Archaeology has been attempting to explain the purpose of medieval hemispherical artefacts called glass smoothers, found in much of Europe, for a century and a half. The oldest and most widespread opinion considers them to be tools designed for the care of clothing. This article presents the results of SEM observations of the surface of selected specimens. The identification of streaks of non-ferrous, especially precious metals, shows that they were intended for another purpose. After discussing the anthropological contexts, including burial finds, the authors conclude that glass smoothers were developed and primarily intended for gilding murals with metal leaves. The inertness of glass to mercury also made it possible to use these artefacts in another method of gilding – amalgamation. It was the contact with precious metal that justified the transformation of a glass smoother on the occasion of a funeral from a working tool into an object with symbolic value. Therefore, the occurrence of glass smoothers in graves cannot be associated with the activities of the deceased individual.

КОЛЛЕКЦИЯ СРЕДНЕВЕКОВОГО СТЕКЛА ИЗ РАСКОПОК Г. ТИГРАНАКЕРТ В АРЦАХЕ / ԱՐՑԱԽԻ ՏԻԳՐԱՆԱԿԵՐՏԻ ՄԻՋՆԱԴԱՐՅԱՆ ԱՊԱԿԻՆ / MEDIEVAL GLASS FROM TIGRANAKERT CITY IN ARTSAKH

The collection of medieval glass from Tigranakert city in Artsakh is consists of 1545 items. Fragments of medieval glassware were found in the cultural layers of the 5th-7th, 9th-11th and 12th-13th centuries in the Central District, as well as in the 12th-13th century layer in the Fortified District. It should be noted, that the remains of glass production - the furnace and the stone smelter for glass - were opened in the excavation of the Medieval Square in the Central District. This indicated on the local production of glass. The furnace is round laid out from bricked in 5 rows: the bricks are burnt, many are broken in to half. The inner diameter of the furnace is 0.78 m. The inside of the furnace was filled with pieces of brick and tiles. This glass workshop probably belonged to the type where the glass was not boiled, but processed by melting pieces of glass. The small pieces of such glass were found in the excavation site. Judging by the excavation layer, it belonged to the early medieval period. The operating time of a similar furnace is limited by the 5-6 years, but the tradition of glass production was preserved later. So, manufacturing defects from glass bracelets production were found in the layers of the 11th-12th centuries. The whole mass of glass objects, according to the meaning of their use, can be divided into two groups: jewelry (bracelets and beads) and vessels, among which a group of oil lamps can be distinguished. Unfortunately, no complete vessels have been found and the glass fragments sometimes are quite small, so through them it is difficult to understand the shape and use of the vessels.

Dating Nathan: The Oldest Stained Glass Window in England?

Relatively little is known about stained glass windows in England predating c. 1170; however, art-historical evaluation by Caviness (1987) argued that four figures from the “Ancestors series” of Canterbury Cathedral, usually dated to the late 12th and early 13th century, in fact date earlier (c. 1130–1160). This would place them amongst the earliest stained glass in England, and the world. Building on our previous work, we address Caviness’s hypothesis using a methodology based upon analysis of a few, well-measured heavy trace elements and a 3D-printed attachment for a pXRF spectrometer that facilitates in situ analysis. The results confirm two major periods of “recycling” or re-using medieval glass. The first is consistent with Caviness’s argument that figures predating the 1174 fire were reused in the early 13th century. The results suggest that in addition to figures, ornamental borders were reused, indicating the presence of more early glass than previously thought. In the second period of recycling (1790s), surviving figures from the Ancestors series were removed and adapted into rectangular panels for insertion into large Perpendicular-style windows elsewhere in the cathedral. The results show that the glasses used to adapt the panels to a rectangular shape were broadly contemporary with the glasses used to glaze the original Ancestors windows, again representing a more extensive presence of medieval glass in the windows.

Gambassini on the road. Underpinning evidence for a medieval widespread glass production in the north Adriatic area

The paper discusses historic, chrono-typological and archaeometric data related to two assemblages of late medieval drinking glass vessels from the monastic complex of San Severo (Ravenna, Italy) and the castle of Rontana (province of Ravenna, Italy). Though standing as different types of settlements, the two sites are linked by the occurrence of a specific beaker among unearthed finds, known as gambassino (or ganbasino) and named after Gambassi, a location in the province of Florence, in Tuscany, believed to be the place where the manufacture of the gambassini originated. The present study, carried out through an integrated use of different disciplines, has provided insights into the production and circulation of this form, extremely common in the late medieval period. Comparative chrono-typological study highlighted no relevant morphological differences among assemblages, with recurrent sizes and decorative patterns. Archaeometric study allowed the identification of various compositional groups pointing to different vitrifying and fluxing agents, although all samples can be classified as plant ash glass; chemical data also show comparability between the gambassini from both sites here considered and Medieval glass sets from the Adriatic area found on the Italian territory and in the Balkans. The displacements of artisans and the circulation of raw materials, the recurrence of this beaker in numerous excavation contexts in the northern Adriatic area - with evidence from the Balkans and Europe - as well as the identification of compositional groups different from each other, but overlapping among assemblages, support the model of a “widespread production” of gambassini. The proposed scenario is further validated from the economic sustainability point of view, considering the production and supply of an object for everyday use and not exclusively dedicated to the élites.

Raw materials and technology of Medieval Glass from Venice: The Basilica of SS. Maria e Donato in Murano

Assemblages of medieval glass from Venice, the leading glassmaking centre in Europe, are rarely accessible for analysis. Here we present electron microprobe analyses of sixty-one glass vessels dated to between the 12th and15th centuries from the island of Murano, which from the late 13th century was the centre of glass production in the city. All appear to have used the same type of soda ash, with similar levels of soda, magnesia, potash and phosphate and this is likely to have originated in the Levant. The alumina, iron and titanium contents suggest that three different silica sources have been used for the glass. Comparison with the available data from Venice and elsewhere in northern Italy suggests that the assemblage may include material made on the island. Furthermore, there are similarities with glass from the Levant and Egypt raising the possibility that raw glass from several regions may be represented. However, records indicate that Venice imported sand as well as raw glass from the Levant, which remains a possibility in the present case.

Thirteenth-century stained glass windows of the Sainte-Chapelle in Paris: An insight into medieval glazing work practices

The restoration of the four northern windows of the 13th century Sainte-Chapelle in Paris from 2011 to 2014 has offered a unique opportunity to investigate the chemical composition and color of medieval glasses. This impressive corpus, covering a total surface of 660 m2, was created in a record time of a few years. The glasses from ten selected panels were analyzed using non-destructive and non-invasive techniques, with a specific consideration for the color of the glasses. Ion beam analyses performed at the New AGLAE facility enabled revealing that all ancient glasses are “potash” type glasses made from plant ashes, likely beech, in agreement with previous results on off-site panels. The multivariate analysis of major and minor elements demonstrates the presence of compositional clusters with a small variability suggesting the identification of bundles of glasses. The coloration of the glasses was measured by optical absorption spectroscopy, using a mobile spectrophotometer over the entire UV–visible-NIR energy range. The color palette is made of six colors assigned to typical medieval recipes. The chromophores of the different glasses are identified by combining the chemical composition, optical absorption spectroscopy and colorimetry. Colorless, yellow and purple glasses arise from the subtle redox equilibrium between manganese and iron. Their reduced usage shows their uncertain production. Blue glasses are colored by Co2+ using saffre from the contemporary German mines, green glasses are colored by Cu2+ and Fe3+ using high concentrations of copper and red glasses are striated glass colored by metallic copper nano-particles. Glass matrix and chromophores form compositional clusters, which are spread among the panels of the four windows suggesting that the glazing of these four windows was run simultaneously by the same atelier using the same supply of glass.

Of Beads and Burials: A Microwear and Experimental Study of Early Medieval Glass and Amber Beads from the Merovingian Site of Lent-Lentseveld

Across Europe, hundreds of thousands of beads have been found in graves dating to the early medieval Merovingian period of 400-750 AD. Whilst recent studies have used microwear analysis to investigate amber beads, there are no known experimental microwear studies examining glass beads. This study proposes a methodological approach using experimental archaeology to explore the limits of microwear analysis for glass beads. This study examines two strings of beads from Lent-Lentseveld in the Netherlands. As the first experimental programme focused on the replica of use-wear on glass beads, this study includes different setups to test for use-wear development in different conditions. Experiments include a tumbling, string, and handling experiment, as well as the examination of Iron-Age re-enactment beads. Microwear analysis is conducted on 116 beads using a stereomicroscope, with magnifications of up to 160x. Analysis has shown that 100 or 150 hours is not enough for certain traces to develop on the experimental beads, with clear traces forming only from the string experiment. By comparing known traces from the experimental beads with the re-enactment beads and then with the archaeological beads, this study provides a framework for examining microwear traces on archaeological beads, particularly glass. This thesis presents the hypothesised biographies of these beads, with some beads displaying traces indicating higher degrees of wear and other beads displaying low to minimal traces of wear. Some beads are also interpreted as being acquired for the individual, whilst other beads are interpreted as having been heirlooms.

(D.F.) Grose The Hellenistic, Roman, and Medieval Glass from Cosa. Edited by R.T. Scott. (Memoirs of the American Academy in Rome, Supplementary Volume 12.) Pp. 247, maps, pls. Ann Arbor: The University of Michigan Press for the American Academy in Rome, 2017. Cased, US$80. ISBN: 978-0-172-13062-7.

(D.F.) Grose The Hellenistic, Roman, and Medieval Glass from Cosa. Edited by R.T. Scott. (Memoirs of the American Academy in Rome, Supplementary Volume 12.) Pp. 247, maps, pls. Ann Arbor: The University of Michigan Press for the American Academy in Rome, 2017. Cased, US$80. ISBN: 978-0-172-13062-7.

Alteration rate of medieval potash-lime silicate glass as a function of pH and temperature: A low pH-dependent dissolution

Potash lime silicate glasses were extensively used during the Middle Ages as components of stained glass windows. Their external faces have been subjected to alteration in the atmospheric medium for centuries, leading to the development of thick alteration layers on the surfaces. This alteration is mainly caused by water in liquid (rainfall) or gaseous (vapor) form. In order to implement geochemical models simulating the long-term behavior of these glasses by coupling the different atmospheric factors, it is necessary to study mechanisms and kinetics of alteration induced by these different hygroscopic situations (rainfall and relative humidity). The aim of this study is here to evaluate the impact of liquid water on stained glass windows and especially to determine alteration rate laws of dissolution and interdiffusion as a function of pH and temperature. For that, a medieval model glass was altered in aqueous solution in batch experiments at different pH values (from 2 to 11), temperatures (from 5 to 70 °C) and saturation states of the solution. From the elemental concentrations in solution, the release rate of elements was calculated and the pH- and T-dependencies were determined. The dissolution and interdiffusion rate laws can now be used to simulate the alteration of a medieval glass submitted to a rainfall event. Moreover, this study highlights that the Si-K-Ca medieval glass presents a very low pH-dependency at alkaline pH, which can be explained by its composition.

Past human impact in a mountain forest: geoarchaeology of a medieval glass production and charcoal hearth site in the Erzgebirge, Germany

Since the twelfth century, forest areas in the upper reaches of the low mountain ranges of central Europe provided an important source of wood and charcoal especially for mining and smelting as well as glass production. In this case study from a site in the upper Erzgebirge region (Ore Mountains), results from archeological, geophysical, pedo-sedimentological, geochemical, anthracological, and palynological analyses have been closely linked to allow for a diachronic reconstruction of changing land use and varying intensities of human impact with a special focus on the fourteenth to the twentieth century. While human presence during the thirteenth century can only be assumed from archeological material, the establishment of glass kilns together with quartz mining shafts during the fourteenth century has left behind more prominent traces in the landscape. However, although glass production is generally assumed to have caused intensive deforestation, the impact on this site appears rather weak compared to the sixteenth century onwards, when charcoal production, probably associated with emerging mining activities in the region, became important. Local deforestation and soil erosion has been associated mainly with this later phase of charcoal production and may indicate that the human impact of glass production is sometimes overestimated.

Glassmaking in medieval technical literature in the Iberian Peninsula

ABSTRACT This paper examines glassmaking in medieval Iberia from the point of view of technical literature, especially recipe books and alchemical treatises, in an attempt to assess to what extent this literary genre (if it is to be defined as such) may have affected, or have been affected by, technological developments in glassmaking between the eighth and sixteenth centuries. Iberian technical literature on the making of glass is put in connection with broader European and Mediterranean trends in the transmission of technical knowledge, the nature of scribal culture and the impact caused by the dissemination of the printing press. Ultimately, the paper aims to review the relationship that exists between the authors of technical literature and contemporary workshop practice, not only taking the written word as evidence, but also using the understanding provided by other fields of research, such as the study of the chemical characterization of medieval glass.

Appied Nuclear Physics-Advanced Ion Beam Materials Analysis at small Accelerators

The ossendorf Ion Beam Laboratory has been developed to an international large scale user facility in the field of ion beam physics and ion beam materials research. The laboratory operates a large number of modern experimental equipment at three MeV accelerators, three implanters, an ECR source and a FIB which together pro- vide almost all ions species in a wide energy range from a few hundred eV to a few ten MeV. Also IBAD and PHI devices were installed for various purposes. The re- search stations at the accelerators are supplemented by complementary techniques like TEM, SEM, AUGER, AFM etc., all contributing useful information to thin film investigations. In this paper a short overview of the laboratory is given and a few recent experiments and their results are shown. Rutherford Backscattering Spec- trometry ( RBS) and Elastic Recoil Detection Analysis (ERDA) are well established techniques for quantitative thin film. The advantage of these methods consists in the simple physics they are basing on, namely the stopping of energetic ions in matter and the binary scattering of at the Coulomb potential of atomic nuclei. The increasing importance of ultra-thin layers for novel technologies demands quantita- tive analysis techniques with a depth resolution of atomic monolayers, which can be obtained for RBS and ERDA by magnetic spectrometers only. The magnetic spec- trometers we have installed at the 3 MV Tandetron and at the 5 MV tandem are described , recent applications are shown and a few problems to achieve high depth resolution will be discussed. Heavy ion detectors as Bragg IC, dE-Erest-telescopes and ToF spectrometers, developed for nuclear physics experiments, are now applied for ERDA, providing an efficient analysis of thin films containing light elements. The lateral position resolution of such detectors enables kinematic corrections and allows large solid angles. Thus by ERDA in situ studies during surface modification processes are possible like in the case of the nitridation of aluminum and stainless steel. At the external beam mainly objects of fine arts or of historical value are analysed. It will be shown, how the complementary application of PIXE, RBS and PIGE can help to detect the beginning corrosion of mediaeval glass objects.