annales

ANNALES du 20e CONGRÈS de l’ASSOCIATION INTERNATIONALE pour l’HISTOIRE du VERRE Fribourg / Romont 7–11 septembre 2015

This volume is sponsored by Vitrocentre and Vitromusée Romont and by anonymous donators

Editors Sophie Wolf, Anne de Pury-Gysel Editing Committee Erwin Baumgartner, Sylvia Fünfschilling, Marion Gartenmeister, Anne de Pury-Gysel, Stefan Trümpler, Sophie Wolf

www.vitrocentre.ch

Scientific Committee Anastassios Antonaras, Françoise Barbe, Erwin Baumgartner, Uta Bergmann, Isabelle Biron, Brigitte Borell, Sally Cottam, Patrick Degryse, Maria Grazia Diani, Anna-Barbara Follmann-Schulz, Danièle Foy, Ian Freestone, Sylvia Fünfschilling, Bernard Gratuze, Susanne Greiff, Yael Gorin-Rosen, Despina Ignatiadou, Caroline Jackson, Yves Jolidon, Dedo von Kerssenbrock-Krosigk, Stephen Koob, Ingeborg Krueger, James Lankton, Irena Lazar, Isabelle Lecocq, Reino Liefkes, Dave Lüthi, Teresa Medici, Marie-Dominique Nenna, Sarah Paynter, Jennifer Price, Anne de Pury-Gysel, Thilo Rehren, Helmut Ricke, Beat Rütti, Lucia Saguì, Flora Silvano, E. Marianne Stern, Stefan Trümpler, Marco Verità, Sophie Wolf Layout Andrea Engl and fischbacher & vock Cover and book design fischbacher & vock AIHV Association Internationale pour l’Histoire du Verre International Association for the History of Glass Internationale Vereinigung für die Geschichte des Glases www.aihv.org © AIHV and authors Romont 2017

Gesamtherstellung

Cover illustration Goblets with white filigree decoration, produced in Swiss glasshouses, late 17th to early 18th century. From different Swiss public and private collections. For a detailed discussion see: Erwin Baumgartner, Reflets de Venise, Bern 2015, p. 254–272, 322–328 and the contribution of Christophe Gerber in the present volume, page 564.

Verlag Marie Leidorf GmbH, Geschäftsführer: Dr. Bert Wiegel, Stellerloh 65 · D-32369 Rahden/Westf. Tel.: +49/(0)5771/9510-74 · Fax: +49/(0)5771/9510-75 E-Mail: [email protected] Homepage: www.vml.de Gedruckt auf alterungsbeständigem Papier Druck: druckhaus köthen GmbH&Co. KG, Köthen ISBN 978-3-86757-024-4

AIHV Annales du 20e Congrès 2015

CONTENTS XI PRÉFACE XIII PREFACE XV VORWORT Sylvia Fünfschilling ANTIQUE AND ISLAMIC GLASS (KEYNOTES) 2

L’étude du verre antique. Etat de la question Marie-Dominique Nenna

10

Entre Orient et Occident, le verre islamique (VIIIe–XIIIe siècle) : apports récents et réflexions sur les échanges et les influences Danièle Foy

ARCHAIC, CLASSICAL AND HELLENISTIC GLASS 36

Glass fragments from Qal’eh Kali, an Achaemenid site in south-western Iran Bernadette McCall, Amanda J. Dusting

43

Capacity measurement to demonstrate standardised productions of the core-formed vessels from the late Archaic to the late Hellenistic period. An interim report Peter Cosyns, Bieke Verhelst, Karin Nys

48

The provenance of Hellenistic core-formed vessels from Satricum, Italy Artemios Oikonomou, Marijke Gnade, Julian Henderson, Simon Chenery, Nikos Zacharias

54

Glass vessels from the Persian and Hellenistic administrative building at Tel Kedesh, Israel Katherine A. Larson, Andrea M. Berlin, Sharon Herbert

61

Gold in glass Despina Ignatiadou

68

A study of the cut gold leaf decoration techniques on ancient gold sandwich glass, with emphasis on the Hellenistic ‘Kirikane’ technique Hidetoshi Namiki, Yasuko Fuji

73

Hellenistic mosaic glass and La Tène glass-working Natalie Venclová, Šárka Jonášová, Tomáš Vaculoviˇc

ROMAN GLASS 82

Gold-band glass fragments in the Römisch-Germanisches Museum of Cologne: considerations about the techniques Giulia Cesarin

87

La vaisselle en verre de deux sépultures aristocratiques augusto-tibériennes à Ath/Ghislenghien (Province de Hainaut, Belgique) Frédéric Hanut, Véronique Danese

92

Le verre romain de Montignac-sur-Vézère (Dordogne) Laure Simon

98

The Roman necropolis of Budva (Montenegro) and its mould-blown glass assemblage Irena Lazar

103

Mold-blown glass from the Roman province of Dalmatia Berislav Štefanac

109

Römische Tintenfässer Isings 77 Michael Johannes Klein

116

A comparative investigation of the glass vessels and objects from eastern Thrace and Lydian tumuli in the light of the Dü˘g üncülü and Güre finds Ömür Dünya Çakmaklı, Emre Ta¸stemür

V

Contents

124

Le sanctuaire d’Yvonand-Mordagne (Vaud, Suisse) : premier aperçu de la vaisselle cultuelle en verre Chantal Martin Pruvot, Ellinor Stucki

132

Blown mosaic glass of the Roman period: technical observations and experiments E. Marianne Stern

140

Two polychrome mosaic bowls and associated glass vessels from a rich 2nd century burial at Kelshall, Hertfordshire, England Sally Cottam, Jennifer Price

145

Früh- und mittelkaiserzeitliche Glasgefäße im nördlichen Obergermanien Martin Grünewald

152

L’exceptionnelle verrerie d’un bûcher funéraire du IIIe siècle après J.-C. de Jaunay-Clan (Vienne, France) Laudine Robin

160

Le verre archéologique du Canton du Tessin (Suisse) : une révision Simonetta Biaggio-Simona

163

More glass from Aquileia (Italy) Luciana Mandruzzato

LATE ROMAN AND EARLY MEDIEVAL 168

Mapping glass production in Italy. Looking through the first millenium AD Barbara Lepri, Lucia Saguì

175

Chemical signature and scale of production of primary glass factories around the Mediterranean in the first millenium AD Patrick Degryse

181

The cut-glass beaker from Biel-Mett/BE Sylvia Fünfschilling

184

New evidence about engraved glass from Milan (Italy) (3rd–4th century AD) Marina Uboldi

190

Besondere Glasfunde aus dem Gräberfeld Gönnheim (Kreis Bad Dürkheim) – Germania prima – und ein neuer Ort möglicher Glasverarbeitung Andrea Ideli

194

Glass vessels from Late Roman burials in Languedoc-Roussillon (France): key points, from glass production to the ritual of grave deposits Stéphanie Raux

203

Late antique and early medieval glass vessels from northern-central Apulia: productions, typologies, functions and circulation Francesca Giannetti, Roberta Giuliani, Maria Turchiano

209

A large glass dish from Cástulo (Linares – Jaén, Spain) with an engraved representation of Christ in Majesty David Expósito Mangas, Marcelo Castro López, Francisco Arias de Haro, José Manuel Pedrosa Luque, Bautista Ceprián del Castillo

213

Late Roman glass from Mala Kopašnica (Serbia) – forms and chemical analysis Sonja Stamenkovi´c, Susanne Greiff, Sonngard Hartmann

222

Glass vessels from Late Roman graves in the Hungarian part of the Roman province Pannonia Kata Dévai

230

Recent glass finds from Elaiussa Sebaste in Cilicia Ci˘ ¸ gdem Gençler-Güray

235

Indices d’ateliers de verriers à Apamée de Syrie, à la fin de l’Antiquité Danièle Foy, avec la collaboration de Bernard Gratuze

240

Une mosaïque de verre à thème chrétien (Ve s.), du site monastique copte des Kellia (Basse-Égypte) Denis Weidmann

243

New finds of mosaic glass inlays from Antinoupolis, Egypt Flora Silvano

VI

Contents

248

Glass bead trade in northeast Africa in the Roman period. A view according to the Museum of Archaeology University of Stavanger assemblage Joanna Then-Obłuska, Barbara Wagner

257

A Late Roman glass workshop at Komarov (Middle Dniester) and the problem of the origin of ‘Barbarian’ facet cut beakers Olga Rumyantseva, Constantin Belikov

265

The glass collections in the ‘Museum Aan de Stroom’ (MAS), Antwerp (Belgium) Eugène Warmenbol, Annemie De Vos, Peter Cosyns

271

Le verre de la nécropole mérovingienne de La Mézière (Bretagne, France) Françoise Labaune-Jean

BYZANTINE AND ISLAMIC GLASS, NEAR EAST 280

Opaque red glass tesserae from Roman and early-Byzantine sites of north-eastern Italy: new light on production technologies Sarah Maltoni, Alberta Silvestri, Gianmario Molin

288

The Early Islamic green lead glass from the excavations at Caesarea Maritima, Israel Rachel Pollak

293

Study on the Early Islamic glass excavated in Paykend in the Bukhara Oasis, Uzbekistan Yoko Shindo

300

Reexamination of a Mamluk glass collection from Jerusalem Naama Brosh

307

Mamluk glass from Quseir al-Qadim: chemical analysis of some glass fragments Laure Dussubieux

313

An outstanding glass assemblage from the medieval and Ottoman castle at Safed (Zefat) . Natalya Katsnelson, with a contribution by Matt Phelps

319

Byzantine glass bracelets in Western Rus. Archaeological finds from Belarus Кristina A. Lavysh

EUROPEAN GLASS FROM 700 TO 1500 326

Red and orange high-alumina glass beads in 7th and 8th century Scandinavia: evidence for long distance trade and local fabrication Torben Sode, Bernard Gratuze, James W. Lankton

334

Evolution of glass recipes during the Early Middle Ages in France: analytical evidence of multiple solutions adapted to local contexts Inès Pactat, Magalie Guérit, Laure Simon, Bernard Gratuze, Stéphanie Raux, Céline Aunay

341

‘The Emerald of Charlemagne’: new observations on the production techniques and provenance of an enigmatic glass artefact Cordula M. Kessler, Sophie Wolf, Jürg Goll

346

Les verres du Haut Moyen Âge issus des fouilles du monasterium Habendum (Saint-Amé, Vosges) Hubert Cabart (†), Inès Pactat, Bernard Gratuze, avec la collaboration de Charles Kraemer et Thomas Chenal

354

Technological transition in early medieval northern Italy: preliminary data for Comacchio glass Camilla Bertini, Julian Henderson, Sauro Gelichi, Elena Basso, Maria Pia Riccardi, Margherita Ferri

360

Where does the medieval glass from San Genesio (Pisa, Italy) come from? Marja Mendera, Federico Cantini, Alessandra Marcante, Alberta Silvestri, Filomena Gallo, Gianmario Molin, Marco Pescarin Volpato

366

Natron and plant ash glass in the Middle Danube region during the Early Middle Ages Danica Staššíková-Štukovská

374

Glass in fashion and trade in Bohemia in the 9th-11th century (archaeology and archaeometry) Kateˇrina Tomková, Šárka Jonášová, Zuzana Zlámalová Cílová

VII

Contents

379

13th–14th century glass in northwest Bohemia: typology, archaeometry and provenance ˇ Eva Cerná

385

Glass production in medieval Spain: a long-term perspective on knowledge transfer Chloë N. Duckworth

391

Die Glaserzeugnisse Bolgars und ihr Verhältnis zu anderen mittelalterlichen Glasproduktionen Svetlana Valiulina

399

Glass from Enez (ancient Ainos) Üzlifat Canav-Özgümü¸s, Serra Kanyak

403

Indices de travail du verre rouge dans l’atelier médiéval d’Anlier, seconde moitié du XIVe siècle (Luxembourg belge) Chantal Fontaine-Hodiamont, Denis Henrotay

EUROPEAN GLASS FROM 1500 TO 2000 412

Looking through late medieval and early modern glass in Portugal Teresa Medici, Inês Coutinho, Luís C. Alves, Bernard Gratuze, Márcia Vilarigues

421

La consommation du verre à Paris entre le XIVe et le XIXe siècle : des données récentes Amélie A. Berthon, Isabelle Caillot, Kateline Ducat

429

Zur Frage der Provenienz von historischen Gläsern – Die Sammlung des Herzog Anton Ulrich-Museums in Braunschweig und des Rijksmuseums Amsterdam Nicole Brüderle-Krug

435

Les verres émaillés vénitiens de la Renaissance : le projet Cristallo Françoise Barbe, Fernando Filipponi

444

Renaissance Venetian enamelled glass. Genuine, façon de Venise and fake or copy artefacts Marco Verità, Isabelle Biron

453

All-glass hybrids: Why they were made and the importance of identifying them Suzanne Higgott

460

All-glass hybrids: What they are, manufacturing techniques and detection Juanita Navarro

467

Venedig oder Tirol? Zur Lokalisierung einiger Hohlgläser des 16. Jahrhunderts mit Kaltbemalung im Bayerischen Nationalmuseum Annette Schommers

474

Glashütte Hall in Tirol. Die archäologischen Grabungen 2008 und 2009 Anna Awad

482

Goblets of the late- to post-medieval period from archaeological excavations in Dubrovnik Nikolina Topi´c

490

16th-century glass vessels from the burials of the Ascension Convent in the Moscow Kremlin Ekaterina Stolyarova

495

The problem of forgeries in 19th century Murano Aldo Bova

498

Deutsche Formgläser des 16. und 17. Jahrhunderts? Beobachtungen und Überlegungen zu einer Neudatierung Dieter Schaich

506

Die älteren Glashütten der Schweiz (ca. 1200–1800) Walter Schaffner

512

„À la façon de Venise“: Zur Geschichte des Begriffs und zur Verbreitung von Gläsern in venezianischer Art in Westfalen Sveva Gai

522

Haushalt, Apotheke oder Gasthaus? Zusammensetzungen frühneuzeitlicher Glasfundkomplexe im Kontext ihrer Fundsituation Birgit Kulessa

VIII

Contents

532

Mirrors, spectacles and looking glasses in Antwerp and the Duchy of Brabant: aspects of production and use of optical glass based on serial documentary and archaeological evidence Danielle Caluwé

537

Façon de Venise, une étiquette problématique. Propositions pour une méthodologie raisonnée de l’étude de la verrerie à l’italienne en Europe, XVe–XVIIIe siècle, à partir de l’exemple du marché parisien (1550–1665) Benoît Painchart, Christiane Guyomar

542

Diagnostic differences between early filigree glass and the Rosenborg Castle-type filigree glass Kitty Laméris

547

The golden age of Amsterdam glass. A chemical and typological approach to recognize Amsterdam 17th century glass production Michel Hulst, Jerzy J. Kunicki-Goldfinger

554

What’s the purpose: oil lamp, perfume sprinkler or trick-glass? Reino Liefkes

561

Court, Pâturage de l’Envers : une verrerie forestière du début du XVIIIe siècle entre tradition et modernité (Jura bernois, Suisse) Christophe Gerber

567

Der Kühlprozess der Glashütte von Court, Pâturage de l’Envers (1699–1714) im Berner Jura (Schweiz) Jonathan Frey

575

Quelques révélations sur l’outillage de la verrerie du Pâturage de l’Envers à Court (1699–1714) Lara Tremblay

578

Eighteenth century lead glass in the Netherlands Anna Laméris

585

Imported beads in Russia in the 17th and first half of the 18th centuries (Moscow, Mangazeya, Smolensk region) Julia Likhter

591

„Pressglas“ aus Benedict Vivats Glasfabriken Valentina Bevc Varl

597

Glass fishing floats from Greek sites Anastassios Antonaras

602

Crizzling glass – corrosion products and chemical composition of Bohemian glass Zuzana Zlámalová Cílová, Helena Brožková, Michaela Knˇezu° Knížová, Irena Kuˇcerová

606

The development of the chemical composition of Czech mosaic glass from the Middle Ages to the present day Michaela Knˇezu° Knížová, Zuzana Zlámalová Cílová, Irena Kuˇcerová, Martin Zlámal

612

The glass collection of Felice Barnabei at the Museo Nazionale Romano – Palazzo Massimo in Rome Giulia Giovanetti, Silvia Bruni

617

Zwei vernachlässigte Glasvarietäten des 19. Jahrhunderts: Aventurin-Hohlglas und Uran-Selenglas Sibylle Jargstorf

621

The Glass Room of the National Palace of Necessidades in Lisbon Alexandra Rodrigues, Bruno Martinho, Frederik Berger, Anísio Franco, Márcia Vilarigues

625

Albert Dammouse (1848–1926) et la pâte de verre (1897–1913) Véronique Ayroles

631

Le verre artistique de Saint-Prex (1928-1964) Stanislas Anthonioz, Ana Quintero Pérez

ASIAN GLASS 640

A unique glass object from a Buddhist context in Sri Lanka Brigitte Borell

647

Glass exchange and people in ancient East Asia Chizuko Kotera

IX

Contents

652

Glass from Mughal India. A study of four eighteenth century cobalt blue bottles Tara Desjardins

WINDOW GLASS AND STAINED GLASS 660

The early medieval stained glass windows from St. John, Müstair: materials, provenance and production technology Sophie Wolf, Cordula M. Kessler, Jürg Goll, Stefan Trümpler, Patrick Degryse

668

Painted window glasses from Akko/Acre from the Crusader period (1099–1291 CE). Manufacturing processes and conservation Adrienne Ganor

672

Medieval window glass in Scotland Helen Spencer, Craig Kennedy

680

Untersuchungen zur Provenienz von Gläsern aus dem Kloster Maulbronn Manfred Torge

684 Swiss Kabinettscheiben from a 19th century Portuguese collection. Study and chemical characterisation Andreia Machado, Alexandra Rodrigues, Mathilda Coutinho, Luís C. Alves, Victoria Corregidor, Rui C. da Silva, Vincent Serneels, Ildiko Katona Serneels, Sophie Wolf, Stefan Trümpler, Márcia Vilarigues 689

Le vitrail dans les hôtels suisses de la Belle-Epoque : une importance sous-estimée ? Dave Lüthi

697

„Magisches Licht“ – Glasfenster in der neo-islamischen Architektur Sarah Keller

699

The window glass and stained glass windows of Belém: a cultural history of the Brazilian Amazon region Amanda Corrêa Pinto, Márcia Vilarigues, Thais Sanjad

703

Autour d’un artiste-verrier de la première moitié du XXe siècle. Marcel Poncet (1894-1953) : à la jonction de la peinture et du vitrail Camille Noverraz

706

L’activité créatrice de Paule Ingrand au sein d’ « Art et Verre » (1946 à 1962) Isabelle Lecocq, avec la collaboration de Catherine Thomas

713

Makellos transparent oder mit romantischen Schlieren? Überlegungen zu Sortenvielfalt und Ästhetik des Fensterglases im frühen 20. Jahrhundert mit Fokus auf dem Spiegel- oder Kristallglas Anne Krauter, Ueli Fritz

REVERSE PAINTING ON GLASS 722

Une œuvre du Vitromusée Romont passée à la loupe. Un cabinet de facture napolitaine décoré de plaquettes de verre peintes Elisa Ambrosio

725

La peinture sous verre « savante » en France au XVIIIe siècle : oubliée puis redécouverte Jeannine Geyssant

732

La peinture sous verre chinoise au XVIIIe siècle. Une rencontre artistique Chine – Occident Thierry Audric

735

La peinture sous verre monumentale de l’église paroissiale de Mézières (Fribourg, Suisse) : « La délivrance de Saint Pierre », 1940, par Emilio Maria Beretta Monika Neuner, Yves Jolidon, Pascal Moret

GENERAL THEMES 740

X

Le verre à l’école, un projet pour les jeunes Maria Grazia Diani, Luciana Mandruzzato

AIHV Annales du 20e Congrès 2015

THE DEVELOPMENT OF THE CHEMICAL COMPOSITION OF CZECH MOSAIC GLASS FROM THE MIDDLE AGES TO THE PRESENT DAY Michaela Knˇezu° Knížová, Zuzana Zlámalová Cílová, Irena Kuˇcerová, Martin Zlámal

Fig. 1: The Last Judgement Mosaic (mozaika Posledního soudu), St. Vitus Cathedral, Prague. Photo: M. Knˇez u° Knížová.

ABSTRACT The variations in typology and chemical composition of mosaic glass tesserae were observed with respect to the date of their manufacture. Chemical composition was determined by X-ray fluorescence spectrometry (XRF). Opacifying phases were analysed by X-ray diffraction (XRD), which detected particles based on antimony, fluorides, phosphates and other elements. The glass showing low chemical resistance, in the form of environmental deterioration, is the medieval glass (potassium-calcium) from the Last Judgement Mosaic in Prague. An interesting degradation phenomenon of mosaics is the crumbling of the tesserae core in layers. This type of damage was observed in the mosaics manufactured in Bohemia during the 20th century. Prefabricated mosaic tesserae from the 1950s, which are stuck on an aluminium support, usually are not damaged in the glass material or on the surface. Here the glue, which fixes the tesserae to the support, is degraded.

606

INTRODUCTION Medieval mosaic work is rare in Central Europe. The very first mosaic found in the Bohemian region is the mosaic of the Last Judgment (figure 1), which was created for the Cathedral of St. Vitus in Prague Castle between 1370 and 1371. The provenance of the mosaic glass used here is not unambiguous (figure 2a). However, it can be stated1 that due to the glass chemical composition (see below) it was produced in Central Europe. The tradition of mosaic decorations appeared in Bohemia towards the end of the 19th and 20th centuries. Mosaics imported to the Bohemian territory were elaborated by foreign companies, for example the company of A. Neuhauser, Innsbruck. Italian glass (figure 2b) was primarily applied in mosaic production and was also used by the first well-known Czech mosaic producer Viktor Foerster (1867–1915). 1

Hetteš 1958, 22–30; Jurek and Peˇr ina 2003, 111–117; Pique and Stulik 2004, 137.

The development of the chemical composition of Czech mosaic glass from the Middle Ages to the present day

Fig. 2: a) Medieval glass tesserae, b) Mosaic tesserae used in V. Foerster’s workshop. Photo: I. Kuˇcerová and M. Knˇez u° Knížová.

Fig. 3: c) Prefabricated glass tesserae, d) Sintered glass tesserae. Photo: M. Knˇez u° Knížová.

The first attempts to produce Czech mosaic glass were realised during the short period between the two World Wars. At the end of the 1920s, the ‘Experimental Institute of Glassmaking’ in Hradec Králové focused on the development of this decorative material and so did Rückle’s glassworks. However, commercial production never even started. The first melting of mosaic glass was purportedly realised by Jaroslav Kopal in Vlastiboˇr near Navarov. The workshop belonging to Viktor Foerster’s widow, Marie Foersterová, who lead the workshop after her husband died, used the locally melted glass combined with glass imported from Italy.2 The systematic development and melting of Czech glass to produce mosaic cut tesserae started in 1930s under the management of engineer Michail Ajvaz in Jan Tumpach’s workshop at Prague. Mosaic glass was also melted in other mosaic workshops established in 1937. After the Second World War, the glass for tesserae production primarily originated from the Union glassworks (later known as Borské glass) and the glassworks at Hostomice. After 1948, all mosaic workshops were put under state control and united into ˇ just one workshop called the Czech Mosaic (Ceská mozaika). This workshop was supplied with glass from the glassworks in Jablonec nad Nisou and later also from the glassworks of the Centre of Artistic Crafts (Ústˇredí umˇeleckých ˇ in Škrdlovice (figure 4e). After 1963, smaller rˇemesel – ÚUR) volumes of mosaic glass were directly melted in the mosaic workshop in Prague 7, Letenská Street, which was also supplied by the Luˇcany glassworks. The central mosaic workshop stopped operating after privatisation at the end of 1993. This also meant the end for the workshop equipment, including the laboratory for the production of mosaic glass.3 Another mosaic centre was established in Železný Brod at the beginning of the 1950s. Here, the production of tesserae stemmed from the technology of jewellery production. The production employed identical raw materials and even the same way of forming as jewellery making – pressing by special tongs with jaws forming little cubes, individual mosaic tesserae (figure 3c, figure 4f). The tesserae produced here

represent the so-called prefabricated material – atypical tesserae created (in many cases) from non-opaque glass. By the end of 1950s, the so-called construction mosaic was produced here too. Also at the end of 1950s, small mosaic tesserae were put into larger tiling units to facilitate and speed up the tiling of greater facade areas. Basic tesserae for this mosaic type were shaped by rotation pressing from glass rods. So-called sintered mosaic (figure 3d) started to be manufactured in large volumes in the Jablonec region in the 1960s. These tesserae were shaped by putting damp glass dust in a cold pressing machinery and then sintering it at temperatures above the softening point of the glass. In the 1970s, the inter-est in construction mosaic dropped, which led to a decrease in mosaic manufacture.4 Today, mosaic glass is not produced anymore in Bohemia, and the glass tesserae are mainly imported from Italy (figure 5g). Currently, also various types of cut flat glass are used as a base material to manufacture new mosaic works of art (figure 5h). THE CHEMICAL COMPOSITION OF MOSAIC GLASS IN BOHEMIA A wide range of colours of tesserae is essential for the composition of a mosaic painting. A final colour may be caused by transition metal ions dissolved in the glass matrix and/or by colloidal or crystalline phases known as opacifiers. If the colourant actually forms its own phase (particle dimension is greater than 1 nm), the glass manifests a characteristic light dispersion. Where the particle size is greater than 500 nm, the glass is opaque.5 Mosaic glass is usually tinted glass where the combination of dissolved ions and opacifiers creates the different colours.

2 3

4 5

Foersterová 1939, 4. ˇ Foersterová 1939, 4; Ctyroký 1941, 145–153; Tesaˇr and Klouda 1988; Langhamer 2003, 72–78; Langhamer 2010; Vicherková 2008; Höferová 2012; Adlerová, Hlaveš and Tesaˇr 2003, 404–407. Adlerová, Hlaveš and Tesaˇr 2003, 404–407. Fanderlík 2009.

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Fig. 4: e) Mosaic tesserae used in the second half of the 20th century, f) Special type of prefabricated tesserae from Železný Brod. Photo: M. Knˇez u° Knížová.

Fig. 5: g) Contemporary glass imported from Italy, h) Contemporary flat glass. Photo: M. Knˇez u° Knížová.

THE MEDIEVAL GLASS OF THE ST. VITUS MOSAIC On the basis of the published glass analyses of the Last Judgement Mosaic 6 it can be stated that three types of glass are represented here: a) potassium-calcium glass, b) lead-silicate glass and c) sodium-calcium glass. The potassium-calcium glass represented here has a very high potassium oxide concentration and is a typical Central European glass from the Middle Ages.7 This supports the hypothesis that this material was produced in Bohemia. The silica content is very low (approximately 47 wt.% SiO2), which causes poor chemical resistance and low durability. Objects made of lead-silicate glass from the Middle Ages can be found in our territory, but it is supposed that they were imported from Poland or Russia, where glass artefacts with identical chemical composition were found.8 The content of lead oxide in the tesserae of the mosaic shown in table 1 is rather high (up to 80 wt.% PbO). Sodium-calcium glass tesserae are probably the material, which was applied during the repair works on the Last Judgement Mosaic at the beginning of the 20th century. This means that the tesserae used for these repairs were imported from Italy. The published studies dealing with this mosaic do not assess the glass opacity and represented phases.

(ranging from 10 to 30 wt.% PbO). Lead-rich glass can be melted readily and increases the refractive index and the brilliance of the glass, which are highly desired properties for indented surfaces.9 Furthermore, some samples also displayed potassium oxide in amounts up to 5 wt.% K2O. The silica content is higher than in the medieval glass. However, the values are rather low when compared to other glass types described in this paper (mostly up to 60 wt.% SiO2). Opacifying particles are most often based on antimony compounds (Ca2Sb2O7, Pb2Sb2O7) and fluorides (NaF, CaF2).

ANALYSIS OF TWENTIETH CENTURY MATERIALS For the present study, the chemical composition of glass tesserae was analysed by X-ray fluorescence analysis (spectrometer ARL 9400). X-ray diffraction analysis (diffractometer PANalytical X Pert PRO) was carried out to identify the opacifying phases (table 1). The text presents basic information on the composition and values representing most of the glass types in the given group. Glass used in V. Foerster’s workshop, later directed by M. Foersterová The glass used in this workshop may be classified as sodalime-silica type with an increased content of lead oxide

608

Prefabricated glass tesserae The manufacture of prefabricated glass tesserae derives from jewellery making. This is reflected by the glass composition. Also, this special mosaic glass was made in the same regions/glassworks as the jewellery, and it was a responding to the demand of the fair. The glass is of the sodium-potassiumcalcium type. The content of sodium oxide ranges from 11 to 16 wt.%. Potassium oxide reaches 8.5 wt.% at most, while the calcium oxide content is up to approximately 5 wt.%. The contents of silica range from 64 to 74 wt.%, which provides the glass with a good chemical resistance. These mosaic tesserae usually do not show damage from glass alteration. However, the works of art realised with this material (figure 6) frequently encounter the loss of individual tesserae or larger blocks of them from the aluminium plates to which the tesserae are stuck to with a hot-melt glue; the loss occurs primarily due to the degradation of the glue. The colourfulness of the glass results from the application of ionic or molecular colourants: for example, the blue-turquoise colour is produced by copper oxide, the green colour by chromium in combination with copper. Cadmium sulfide results in a deep yellow colour, together with selenium and sulphur it 6 7 8 9

Hetteš 1958, 22–30; Jurek and Peˇr ina 2003, 111–117; Pique and Stulik 2004, 137. Cílová and Woitsch 2012, 371–380. Hetteš 1958, 22–30. Smrˇ cek and Voldˇr ich 1994.


Fig. 6: Mosaic ‘The Miner with a Girl’ (Horník a dˇevˇce), ˇ íhová. Stonava. Photo: V. R

Fig. 7: Mosaic ‘Day and Night’ (Den a noc), Prague. Photo: M. Knˇez u° Knížová.

yields shades of bright red and orange. A great portion of the prefabricated cubes used for the manufacturing of mosaics is made of clear glass, but occasionally opaque glass is applied here too. In this case, the opacity is caused by dispersed particles of fluorides (for example, NaF, CaF2), phosphates (NaCa(PO4)) or their combination (Ca5(PO4)3F). Sintered glass tesserae The glass used is of the sodium-potassium-calcium type but when compared to the previous groups the content of sodium is lower (ca. 7.5 wt.% Na2O). The content of potassium is roughly 7 wt.% K2O, and the calcium content is approximately up to 15 wt.% CaO. The latter functions as a glass stabilizer. Together with silicon and zinc (content approximately 6 wt.% ZnO), it positively affects the glass’ chemical

resistance – this type of tesserae did not show any distinct corrosive damage. Tesserae of this type were manufactured only from opaque glass. The opacifying agent found here is calcium fluoride (CaF2). The strong opacity of the glass resulted from the increased concentration of this agent (up to 4 wt.% CaF2). This agent was usually added to the glass in the form of cryolite (Na3[AlF6]) or fluorspar (CaF2). Glass used in the second half of the 20th century In this period, a wide range of coloured glass was manufacˇ workshop tured, the origin of which is related to the ÚUR (figure 7) and Czech production. This glass may be divided into two basic groups based on the content of lead oxide: a) glass containing several tens of percent PbO, b) glass in which lead oxide was not detected. The concentrations of

609


PbO

MgO

ZnO

MnO

F

Opacifying particles

4.7

-

2.5

0.2

1.0

-

Unknown

0.3

1.3

3.4

0.1

1.0

-

Unknown

0.2

0.1

80.1

-

0.1

-

-

Unknown

23.9

0.7

0.2

0.2

0.5

-

0.5

-

Unknown

17.8

2.0

0.2

0.2

23.7

-

0.2

0.1

-

Based on antimony

-

16.7

0.9

0.3

0.1

26.7

-

-

0.1

-

Based on antimony

53.9

1.5

15.4

0.8

0.2

0.1

26.3

-

-

-

-

Based on antimony

Blue

48.2

-

15.1

1.1

0.2

1.2

32.7

-

-

0.4

-

Based on antimony

Prefabricated tesserae

Yellow

67.0

11.9

7.6

5.7

1.3

0.1

-

1.4

-

-

1.1

-


Colourless

73.1

5.5

11.8

4.9

0.2

0.3

-

2.7

-

-

-

-


Green

68.4

6.1

11.8

6.9

2.3

0.1

-

-

-

-

0.4

-


Red

66.5

3.9

14.6

2.5

0.2

-

-

-

7.7

-

0.4

-

Sintered tesserae

Yellow

63.2

6.7

7.5

10.2

1.3

0.1

-

0.3

6.1

-

3.7

CaF2

Sintered tesserae

Blue

60.5

3.7

8.9

12.8

3.7

0.4

0.1

0.3

2.8

1.9

3.4

CaF2

Sintered tesserae

White

72.2

4.3

8.6

1.3

12.2

0.4

-

0.1

-

-

0.3

-

Sintered tesserae

Red

64.8

7.4

6.5

8.4

0.2

-

-

-

8.4

-

2.8

CaF2

Glass used in 2nd half of 20th century

White

51.5

8.6

8.6

2.2

4.3

1.9

18.1

-

-

0.7

2.3

CaF2, NaF


Green

57.1

1.7

7.8

2.5

6.8

0.4

14.6

0.1

4.3

-

2.0

Phosphates, CaF2


Red

60.7

5.5

15.1

3.4

1.6

-

-

-

9.1

-

1.7

CdS


Yellow

53.0

5.7

19.8

2.9

4.3

0.1

0.1

-

7.1

-

5.7

CaF2, NaF

Contemporary flat glass

Blue

66.0

3.6

13.2

5.3

6.2

0.1

-

-

1.6

-

3.8

CaF2, NaF


Violet

71.7

0.5

16.1

4.6

2.4

0.2

-

1.0

-

2.0

1.1

-


Orange

64.0

0.8

17.8

7.6

3.7

0.1

-

0.1

2.1

-

3.0

CaF2


Colourless

71.0

0.4

15.8

6.5

1.0

0.1

-

4.0

-

-

-

Type of tesserae

Colour

SiO2

K2O

Na2O

CaO

Al2O3

Fe2O3

Medieval glass*

Red

45.1

23.8

-

18.1

2.0

Medieval glass*

Green

44.6

20.8

-

24.7

0.1

Medieval glass*

Yellow

17.2

-

-

0.4

Medieval glass*

Blue

46.9

25.0

-

Glass used by V. Foerster

Yellow

51.5

-


Green

53.0


Red


-

Table 1: Examples of the chemical composition of tesserae of the various periods; XRF spectrometer ARL 9400 [wt.%] (in the table are specified select oxides) and XRD diffractometer PANanalytical X Pert PRO, * composition taken from Pique and Stulik 2004, 137.

Fig. 8: Crumbling of the cube core. Photo: M. Knˇez u° Knížová.

alkaline and earth alkaline metal oxides as well as the silica content are highly variable. It is obvious that these glass types are the result of many melting experiments. During these experiments, not just one predominant type of glass was used as was the case for the prefabricated or sintered mosaics. The use of a great diversity of raw materials was confirmed for the opacifying agents, which were based on antimony (Ca2Sb2O7), fluorides (NaF and CaF2) and phosphates (Na2Ca(PO4)F). Also, variable contents of zinc oxide are found primarily in the glass coloured in shades of yellow, orange and red. This corresponds with the creation of colours in these glass types using cadmium sulphides or selenides (cadmium was detected in the form of molecular colourant). These cut tesserae showed the deterioration of both the glass surface (differently coloured spots/dots) and the tesserae core (crumbling of the cube core, see figure 8).

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Contemporary glass imported from Italy This group of glass may be divided into: a) non-opaque glass, b) opaque glass. The composition of the glass from the first group (non-opaque) is quite diverse. It contains both glass with comparable contents of sodium and potassium oxides (about 11 wt.%), and also glass with a much lower potassium oxide concentration (roughly 7.5 wt.%) or even no K2O. The glass types with the higher levels of sodium and potassium oxides also show very low concentrations of calcium oxide (up to 0.5 wt.% CaO). The glass with lower sodium and potassium oxide contents was found to contain about 6 wt. % CaO. Again, zinc oxide was found in the glass with yellow, orange and red colours. The majority of the opaque glass has rather high sodium oxide contents (14–18 wt. %) and low potassium and calcium oxide concentrations (K2O often reaching no more than 1 wt.%, CaO up to 2 wt.%). Corresponding closely to the Art Nouveau glass used by V. Foerster (which was also imported from Italy), this glass also contains lead oxide in higher concentrations. The Art Nouveau glass is also similar in that it is opacified by antimony-based particles (also glass pieces opacified with fluorides were found). It can be stated that the composition of Italian Art Nouveau and contemporary tesserae from Italy is still very similar. CONCLUSIONS The glass samples studied are highly variable. Not only the themes of the mosaics but also the chemical composition of the glass used for the tesserae changed over the investigated period. The study confirmed an anticipated relationship between different glass compositions and their fabrication


typologies, with the prefabricated mosaics showing more homogeneous compositions and lower concentrations of some elements. Major differences in composition were detected in the material used in the second half of the 20th century representing the products of Czech workshops. The evaluated material from Italy (the type originally used by V. Foerster’s workshop and the contemporary material) is very similar as far as the shape of cubes and their chemical composition are concerned. These results are very important for any future restoration work on the mosaics of the Art Nouveau period. The study will allow us, if necessary, to use newly produced tesserae to complement older mosaics. ACKNOWLEDGMENTS The authors express their gratitude to the Ministry of Culture Czech Republic (project DF12P01OVV017) for financial support.

Michaela Knˇezu° Knížová Department of Chemical Technology of Monument Conservation University of Chemistry and Technology Prague [email protected] Irena Kuˇcerová Department of Chemical Technology of Monument Conservation University of Chemistry and Technology Prague Zuzana Zlámalová Cílová Department of Glass and Ceramics University of Chemistry and Technology Prague Martin Zlámal Department of Inorganic Technology University of Chemistry and Technology Prague

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