Lead in Glassy Materials in Cultural Heritage E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Geisteswissenschaft
- Sprache: Englisch
Although the development of lead crystal was a major step in the history of glass in the late 17th century, the presence of lead in vitreous matrices (glass and glazes) is much older, dating back to the second millennium BCE.
Lead in Glassy Materials in Cultural Heritage traces the history of these skills and also looks at the most recent developments in materials science concerning the role played by lead in the properties of glass, including coloring. It develops an understanding of weathering processes and notions of the durability of leaded glass. It also examines public health issues and current recommended standards for the use of lead in industrial glass.
This multidisciplinary book is intended for a wide audience: art and technical historians, museum curators, restorers, materials specialists, manufacturers and engineers.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Foreword by Isabelle Pallot-Frossard
Foreword by Daniel R. Neuville
Introduction
PART 1: Overview and Specific Techniques for the Analysis of Lead Glasses and Glaze
1 Overview
1.1. Advantages brought by lead
1.2. Difficulties related to the use of lead oxide
1.3. Conclusion
1.4. References
2 Lead Isotopes for the Study of Ancient Glass
2.1. Lead isotope chemistry
2.2. The use of lead isotopes in archaeology
2.3. Lead isotopic analysis of glassy material
2.4. O, Sr, Nd and B isotopes for studying archaeological glass
2.5. Conclusion and future perspectives
2.6. Acknowledgments
2.7. References
PART 2: Structure of Lead Glasses: Influence on their Properties, Including Color
3 Structure and Properties of Lead Silicate Glasses
3.1. Introduction
3.2. Lead and lead oxides
3.3. Crystal phases and glasses of the SiO
2
-PbO system
3.4. Glasses of the SiO
2
-PbO-R
2
O system (R= Na, K)
3.5. Glasses of the SiO
2
-PbO-Al
2
O
3
system
3.6. Conclusion
3.7. References
4 Optical Properties and Coloration of Lead Silicate Glasses
4.1. Physical bases of optical properties and the origins of glass color
4.2. Optical properties and color of transparent SiO
2
-PbO-M
2
O glasses
4.3. SiO
2
-PbO-M
2
O glasses colored by transition ions
4.4. References
PART 3: History and Evolution of Lead Glasses
5 Lead in the Recipes of the Middle Ages and Renaissance
5.1. The first written sources mentioning the use of lead
5.2. Recipes of translucent and opaque lead glasses from the Middle Ages and Renaissance
5.3. Conclusion
5.4. References
6 The First Lead Glasses
6.1. Introduction
6.2. Glasses of the Eastern Mediterranean from the second and first millennia BC
6.3. Lead glasses in Asia starting with the second half of the first millennium BC
6.4. Medieval lead glasses in Western Europe
6.5. European lead glasses, from the beginning of the modern period until the invention of crystal glass
6.6. Conclusion
6.7. References
7 Lead in Glasses: Recent Times
7.1. The adventure of lead crystal glass
7.2. New colorants of lead glass
7.3. The new opacifiers
7.4. The new processes of crystal glass decoration
7.5. New glassmaking techniques
7.6. Conclusion
7.7. References
8 Early Islamic Lead Glass
8.1. Introduction
1
8.2. Islamic lead silica glass (
mīnā
) from the Near East
8.3. Lead slag glass from Šaqunda (Córdoba)
8.4. Soda ash lead glass from al-Andalus
8.5. Concluding remarks
8.6. References
9 Lead in the Enamels of the Middle Ages and Renaissance
9.1. Limoges champlevé enamels on copper from the Middle Ages
9.2. The so-called Venetian enameled coppers of the Italian Renaissance
9.3. References
PART 4: History, Implementation and Evolution of Lead Glazes
10 History of Lead in Ancient Ceramic Materials
10.1. Introduction
10.2. Properties and implementation of lead glazes
10.3. The first lead glazes
10.4. Dissemination and evolution of the lead glazing technique in the high Antiquity
10.5. Hybridization of lead glazes with other ceramic traditions
10.6. The importance of lead-rich glassy materials in the race for porcelain
10.7. Innovations brought by Islamic potters of the eighth to ninth century: the place of lead glassy materials
10.8. Soft-paste porcelains: lead glaze on translucent paste
10.9. Lead-rich vitrified paints
10.10. Conclusion
10.11. References
Exhibition catalogs
11 Paste–Glaze Interaction
11.1. Context
11.2. Paste–glaze interface
11.3. Factors affecting the paste–glaze interface
11.4. Cross-diffusion of chemical elements
11.5. Morphology of the interface
11.6. Identification of crystalline phases at the interface
11.7. Interface as an indicator of elaboration processes
11.8. Influence of interface on the physical properties
11.9. Conclusion
11.10. References
12 Weathering of Ancient Lead Glazes
12.1. Slightly weathered glazes
12.2. Weak iridescences and pinholes
12.3. Advanced weathering in the context of burial
12.4. Protection of lead-glazed weathered objects by sol-gel methods
12.5. Conclusion
12.6. References
PART 5: Weathering of Lead Glasses and Standards
13 Lead Leaching in Industrial Crystal Glasses: Role of Chemical Composition, Structure and Surface Treatments
13.1. Influence of lead content on crystal glass structure
13.2. Leaching mechanisms of lead glasses
13.3. Industrial surface treatments limiting lead release by crystal glass
13.4. Conclusion
13.5. References
14 Lead in Glass: Standards and Regulations
14.1. Lead uses in glassworks
14.2. Regulations related to lead
14.3. Food contact
14.4. Conclusion
14.5. References
List of Authors
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1. Summary of different measurement methods for determining lead isoto...
Table 2.2. Mathematical models used for mass bias correction
Chapter 4
Table 4.1. Wavenumbers (in cm−1) for which the absorbance normalized to thickn...
Chapter 8
Table 8.1. Mean composition and standard deviations (SD) of the three main Isl...
Chapter 9
Table 9.1. Results of the analyses of type 1 and 2 compositions of Limoges ena...
Table 9.2. Minimum and maximum contents of lead (oxide mass percentage) in Lim...
Table 9.3. Results of analyses (in weight percent of the oxides) of opaque whi...
Chapter 10
Table 10.1. Comparison of chemical compositions of Pb-Ba glasses dating from t...
Table 10.2. Chemical compositions of Han, Tang and Liao lead glazes (weight % ...
Table 10.3. Several examples of compositions of glazes from objects dating fro...
Table 10.4. Chemical compositions of glazes in the Roman and Byzantine worlds....
Table 10.5. Examples of ranges of compositions of Abbassid glazes (Suse and Sa...
Chapter 13
Table 13.1. Glass composition analyses (oxide molar percentage)
Table 13.2. Comparison of the number of non-bridging oxygens (NBOs) calculated...
Table 13.3. The Si, K, Na, Pb and Sb concentrations (mg·L−1) ...
Chapter 14
Table 14.1. Designation according to the Directive of 1969
Table 14.2. Lead release limits according to FDA
Table 14.3. Limits according to ISO 6486-2 and 7086-2 standards
List of Illustrations
Chapter 1
Figure 1.1. Variation of the logarithm of viscosity (in Pa·s) as a ...
Figure 1.2. Variation of the density of lead glasses as a function of PbO cont...
Figure 1.3. Relation between the optical index nD of glasses and their lead co...
Figure 1.4. Abbe diagram giving the refractive index nD of various glasses dep...
Chapter 2
Figure 2.1. Sources of different elements in glass. Full lines are main source...
Figure 2.2. Flowchart allowing to decide what raw material the Sr in glass is ...
Chapter 3
Figure 3.1. Examples of three-dimensional representation of pure silica glass ...
Figure 3.2. Representation of polarizability α of Pb2+ ion and ...
Figure 3.3. Oxygenated environment of the Pb2+ ion and Pb-O distances in two v...
Figure 3.4. Representation in actual proportions of lead ions (in black) and o...
Figure 3.5. Crystal structures of two PbO polymorphs: litharge (a) and massico...
Figure 3.6. Phase diagram of the PbO-SiO2 system (mol%) above 500°C...
Figure 3.7. Crystal structures of three lead silicates (in-depth representatio...
Figure 3.8. Evolution of the Si-O-Si cross-linkage rate per oxygen atom depend...
Figure 3.9. Evolution of the rate of Pb-O-Si and Pb-O-Pb cross-linkage per oxy...
Figure 3.10. Evolution as a function of PbO content of the temperature corresp...
Figure 3.11. Evolution of 29Si MAS NMR spectra of lead silicate glasses depend...
Figure 3.12. Evolution of the relative proportions of Qn units determined from...
Figure 3.13. (a) 17O MAS NMR spectra of lead silicate glasses enriched in 17O ...
Figure 3.14. Evolution of the silicate vitreous network (only SiO4 tetrahedron...
Figure 3.15. Radial distribution functions calculated from the neutron scatter...
Figure 3.16. Structural model of lead silicate glasses proposed by Takaishi et...
Figure 3.17. Local and extended structure of lead silicate glasses (30–65 mol%...
Figure 3.18. Structural model proposed by Alderman for the 35PbO–65SiO2 (mol%)...
Figure 3.19. Structural model proposed by Alderman for 80PbO–20SiO2 glass. To ...
Figure 3.20. 17O MQ-MAS spectrum of a crystal glass (77.1SiO2–10.6PbO–11.3K2O–...
Figure 3.21. Evolution of the glass transition temperature Tg with increasing ...
Figure 3.22. Evolution of viscosity η (in poiseuilles Pl) as a ...
Figure 3.23. Evolution of Raman spectra of ternary SiO2-Al2O3-PbO glasses obta...
Figure 3.24. Evolution of 29Si MAS NMR spectra of ternary SiO2-Al2O3-PbO glass...
Figure 3.25. Comparison of 17O MAS NMR spectra of 60SiO2–40PbO and 51SiO2–34Pb...
Figure 3.26. 17O MQMAS NMR spectra of 60SiO2–40PbO and 51SiO2–34PbO–15Al2O3 gl...
Figure 3.27. Evolution of 27Al MAS NMR spectra of ternary SiO2-Al2O3-PbO glass...
Chapter 4
Figure 4.1. Refractive index and extinction coefficient of the silica glass me...
Figure 4.2. (a) Very simplified diagram of the chemical bond in PbO compound a...
Figure 4.3. Two varnished terracotta jugs by Agnès Cabaret, ceramist...
Figure 4.4. (a) Glass elaboration process with two meltings at temperatures T1...
Figure 4.5. Nominal molar compositions and photographs of nine glasses prepare...
Figure 4.6. Absorption spectra of three “colorless” glasses NaI, NaPbI and PbI...
Figure 4.7. Molar extinction coefficient ε of iron-doped glasses...
Figure 4.8. Molar extinction coefficient ε of copper-doped glasses...
Figure 4.9. Schematic energy level diagrams, using the transition energies exp...
Figure 4.10. Schematic representation of quasi-molecular CuO6 complexes of oct...
Chapter 5
Figure 5.1. Visigoth crown of the 7th century discovered at Guarrazar near Tol...
Figure 5.2. Plique enamel plate preserved in Paris at the National museum of M...
Figure 5.3. Enameled goblet with two sphinxes facing each other, Venice, end o...
Chapter 6
Figure 6.1. Simplified chronology of the fabrication of lead glasses and the u...
Chapter 7
Figure 7.1. Vaseline saltcellar, Saint-Louis museum, toward 1860, photo P. Leh...
Figure 7.2. Example of “overlay” technique (glass in several layers): colorles...
Figure 7.3. Examples of engraving. (a) Brilliant cutting (colorless crystal gl...
Figure 7.4. Example of iridescent glass: Loetz, Bröhan-Museum...
Figure 7.5. Paperweight fabricated at Baccarat by the mid-19th century
2
.
Figure 7.6. Lithograph representing the funeral carriage of Napoleon during th...
Figure 7.7. Optical microscope photograph (reflected light) of a fragment of “...
Chapter 8
Figure 8.1. Emerald green lead silica glass from Samarra: (a) Sam 800.2/Lamm 1...
Figure 8.2. Binary plot of titanium versus aluminum oxide concentrations of th...
Figure 8.3. Lead isotope ratios for early Islamic emerald green lead silica gl...
Figure 8.4. Lead isotope ratios for (a) lead ores from Egypt and (b) lead ores...
Figure 8.5. Lead isotope ratios for Islamic lead glasses and glazes in compari...
Figure 8.6. Comparison of lead silica glass from the eastern Islamic lands wit...
Figure 8.7. Fragment of vessel base (MIR 040) from the lead slag glass...
Figure 8.8. Mold blown beaker from Madīnat al-Zahrā’ made from...
Figure 8.9. Trace elements associated with the lead component in the...
Figure 8.10. Lead isotope ratios for the high lead glasses from...
Chapter 9
Figure 9.1. Eucharistic dove, Limoges, 1215–1235, preserved at the Louvre muse...
Figure 9.2. Funerary plaque of Guy de Meyos, Limoges, 1307, preserved at the L...
Figure 9.3. Scanning electron micrograph in backscattered electrons (BSE) of a...
Figure 9.4. Deep plate, Paris, Louvre museum, inv. R283 (corpus 6 in Barbe et ...
Figure 9.5. Deep bowl with high foot. Paris, Louvre museum, inv. N1221 (corpus...
Figure 9.6. Detail of an opaque turquoise enamel of the deep plate, inv. R283 ...
Figure 9.7. Scanning electron micrograph in backscattered electrons (BSE) of t...
Chapter 10
Figure 10.1. Skyphos with skeletons, Smyrna, fourth quarter of the first centu...
Figure 10.2. Victory, Kymé, second half of the first century BC...
Figure 10.3. Camel, “sancai” ceramics, Tang period (seventh to eighth century)...
Figure 10.4. Detail of the rustic figulines platter (Louvre Museum, inv MR 339...
Figure 10.5. Examples of white and blue Della Robbia glazes: The Virgin adorin...
Figure 10.6. Stratigraphic section of a sample of yellow glaze taken from floo...
Chapter 11
Figure 11.1. Paste–glaze interface of a Palissy-type replica (composition A on...
Figure 11.2. Effect of the glaze mixture composition on interfaces with a kaol...
Figure 11.3. Effect of temperature on the paste–glaze interface of Palissy-typ...
Figure 11.4. Effect of the firing time on the paste–glaze interface of Palissy...
Figure 11.5. Effect of cooling rate on the paste–glaze interface of Palissy-ty...
Figure 11.6. Profiles of Al concentration measured by energy-dispersive X-ray ...
Figure 11.7. Glaze of a Palissy ceramic shard (inventory no. EP341). (a) Inter...
Figure 11.8. Morphology of the paste–glaze interface in an archeological sampl...
Figure 11.9. SiO2 content versus PbO content in the feldspar crystals develope...
Figure 11.10. Analysis of a lead feldspar crystal (K,Ca)PbAl2Si2O8 by electron...
Figure 11.11. Zoned feldspars observed at the paste–glaze interface of a Palis...
Figure 11.12. Analysis of an anorthite crystal (Pb)CaAl2Si2O8 observed by TEM ...
Figure 11.13. Mullite nanocrystals observed within a lead feldspar PbAl2Si2O8 ...
Figure 11.14. Glaze of composition A deposited as frit on biscuit (a) or on ra...
Figure 11.15. Schematic representation of stresses and deformations resulting ...
Chapter 12
Figure 12.1. Example of a slightly weathered glaze: (a) macrophotography of th...
Figure 12.2. Detail of the surface of a Renaissance ceramic shard observed by ...
Figure 12.3. Stratigraphic cross-section of two glazes: (a) Byzantine object; ...
Figure 12.4. Examples of laminated structures on opacified alkali-lead glazes...
Figure 12.5. Detail of a complex weathered zone. It is important to note the p...
Chapter 13
Figure 13.1. 29Si MAS NMR spectra of the Pbx glass series. The dotted lines gi...
Figure 13.2. (a) 17O MAS NMR spectra of Pb10, Pb30 and Pb50 glasses and (b) 17...
Figure 13.3. Distribution of Si-O-Si bond angles for Pb10, Pb30 and Pb50 resul...
Figure 13.4. 3D visualization of lead atoms interconnected by Pb-O-Pb bonds ob...
Figure 13.5. Glass leaching protocol under dynamic conditions with high soluti...
Figure 13.6. Equivalent thickness of leached glass calculated from the release...
Figure 13.7. Equivalent thicknesses of Pb10 glass leached at 22°C...
Figure 13.8. Elementary profiles obtained by ToF-SIMS on Pb10 glass leached at...
Figure 13.9. Comparison between Pb diffusion coefficients obtained...
Figure 13.10. Equivalent thickness of the leached glass calculated from lead r...
Figure 13.11. Elementary profiles obtained by ToF-SIMS after 1 year of leachin...
Figure 13.12. (a) 29Si MAS NMR spectra and (b) 17O MAS NMR spectra of Pb10 gla...
Figure 13.13. Comparison between lead concentrations at 22°C...
Guide
Cover Page
Table of Contents
Title Page
Copyright Page
Foreword by Isabelle Pallot-Frossard
Foreword by Daniel R. Neuville
Introduction
Begin Reading
List of Authors
Index
WILEY END USER LICENSE AGREEMENT
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SCIENCES
Physics of Condensed Matter,Field Directors – Roland Pellenq and Pierre Levitz
Cultural and Industrial Heritage Materials,Subject Head – Philippe Sciau
Lead in Glassy Materials in Cultural Heritage
Coordinated by
Anne Bouquillon
Patrice Lehuédé
First published 2023 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK
www.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA
www.wiley.com
© ISTE Ltd 2023The rights of Anne Bouquillon and Patrice Lehuédé to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2022947641
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78945-076-7
ERC code:PE3 Condensed Matter Physics PE3_13 Structure and dynamics of disordered systems: soft matter (gels, colloids, liquid crystals, etc.), liquids, glasses, defects, etc.SH5 Cultures and Cultural Production SH5_6 History of art and architecture, arts-based research
Foreword by Isabelle Pallot-Frossard
Isabelle PALLOT-FROSSARD
Foundation for Cultural Heritage Sciences, Cergy-Pontoise, France
Glass, a material that man has synthesized for over 5,000 years, has a high heritage value, acquired through successive or simultaneous technical innovations required for its implementation, the multiple uses that civilizations have given to it, and its ubiquity in public collections. Its transparency, brightness, wide color variety and sometimes sonority properties have been explored by man to this day, in order to beautify his prestige objects, items dedicated to liturgical rites, and also those of daily life, to attire oneself, look at his reflection or still protect himself from the surrounding environment by closing up his living space or place of worship without darkening the inside ambiance. This polymorphic material, both resistant and brittle, is justifiably explored by a rich literature in materials science, art history and in history of techniques.
However, this book approaches a subject that is less well known, and which has not until present been the object of a historical and scientific synthesis: that of the combination of glass and lead, in a wide variety of uses and formulations, from glazes on ceramic to lead crystal glass, going through enamels on metal or glass, fake gems, Venetian blown glass, mosaic tesserae and certain pieces of stained glass windows. Due to its multiple properties, lead is omnipresent in various forms in heritage objects, sought-for as coloring agent, opacifier, siccative for oils, appreciated by alchemists and painters, used in pharmacopoeia and at the same time, paradoxically, dreaded since ancient times for its harmful effects on health.
The “marriage” referred to here is a “fusional” one, which integrates lead into the vitreous matrix, in the form of oxides, in order to give it color or on the contrary absence of color for the crystal glass, as fluxing agent to lower its melting temperature, modify its physical and optical properties or enhance its durability. The variety of resulting properties is huge during time and depends on uses. This book highlights the complexity of mechanisms involved, which required of the craftsmen who manufactured these objects relentless experimentations, based on know-how accumulated and transmitted in the workshops. These technical advances are recorded in many technical treatises, whose understanding nowadays is both necessary and difficult for reasons of vocabulary and cultural context, and sometimes of willingness from the authors to describe everything while protecting manufacturing secrets.
This book does not cover the “marriage of convenience”, a term that can be used to qualify the association of colored, cut and painted glass and a lattice of lead cames, whose plasticity was used to closer embed the glass pieces, which is the historical technique of stained glass. Another subject that is not covered here is the “forced marriage” between glass and lead, resulting from external contributions that frequently pollute the surface of glass exposed to the atmospheric environment, to the burial medium or to the close proximity of lead works.
However, the end of the volume deals with the effects of the “divorce” between glass and lead generated by leaching phenomena that alter the objects, particularly the lead glazes having been subjected to burial periods, and that continue in the museum collections. Moreover, the methods implemented for following up the progression of this weathering, in order to prevent it and slow it down or even to stop it, will also be described. The work conducted in the crystal glass industry will thus be understood, which will contribute to a better understanding and prevention of lead leaching in the crystal containers in contact with certain acid drinks, susceptible of harmful effects on human health.
Knowledge of lead glass may be at first sight perceived as a very specialized and limited subject. It is in reality an extremely wide field of research, and this work coordinated by Anne Bouquillon and Patrice Lehuédé is a true invitation to a time and space journey, in the quest for the most varied objects, knowledge of which requires the contribution of the finest techniques of modern chemistry and the history of techniques.
Foreword by Daniel R. Neuville
Daniel R. NEUVILLE1,2
1 IPGP, CNRS, University of Paris, Paris, France
2 USTV, Paris, France
Since ancient times, lead has been a mythical element whose use evolved with human civilizations. It was by turns praised and proscribed: praised due to its abundance, malleability, low melting temperature and its contribution to improving the properties of several materials (glass, ceramic), and also proscribed because of its toxicity (lead poisoning) known since ancient times.
Lead is an abundant element, relatively well distributed at the level of the Earth’s crust. It is generally associated with copper, zinc or silver and therefore relatively easy to find. Lead was used by the first Sumerians who had developed the means to extract and purify it and who used it to color and enamel ceramics, seal amphorae, or produce cosmetics. In summary, lead has been present since ancient times in the common objects of our daily life. In parallel to its daily use, lead is related to alchemy; it is important to mention the works of Gilles de Rais, a figure who is at the origin of Barbe-Bleue. It is both used and feared by pharmacopoeia.
In this book dedicated to lead in vitreous materials of heritage, Anne Bouquillon and Patrice Lehuédé offer a new complete and updated perspective on the role of this element in glasses and glazes. Their book retraces the history and the manufacturing of the first lead glasses, which were in fact glazes covering pottery or opaque massive glasses. This book covers also the famous flintglass or lead crystal, which contributed to the significant progress of optics and astronomy. The more recent history of lead crystal is also approached from the perspective of its risks essentially related to the alteration and lixiviation of crystal.
The reader will find a consideration on the origin of lead used in glasses, the difficulties encountered in making glasses and glazes (Part 1), and also the history and evolution of compositions of lead glasses throughout time and world. This journey of lead in glass leads from the very heart of China to the Vosges forests passing through the Arab world and ancient Rome. This scientific and technical journey is brightened up by a color chase, in which colorless crystal spans across the entire visible spectrum as an actual rainbow, in relation with chromium, copper, iron and all the other transition metals it contains. Part 2 presents a synthesis of current scientific works on the role of lead in glasses. The structural aspects related to the changes of coordination number of lead and their effects on the properties are amply described and commented upon. Part 3 traces back the history of lead glasses throughout the centuries and details the many glass recipes, clandestinely published, for making “proper” lead glass. This part takes us on a voyage across ages and throughout the world in search for the transparency and reflection of lead glass. Part 4 approaches the subject of history, implementation and evolution of lead glazes. These lead-rich glazes and their evolution have marked the history of ceramic and at the same time represent a technological and scientific challenge that is particularly well detailed in this book. As a conclusion, Part 5 approaches the difficult subjects of alteration, leaching and release of lead from the crystal. What is the role of lead escaping from glass in relation with the environment and health? These essential questions, which are at the root of the main critiques brought to lead crystal, are unambiguously explored and discussed here.
This book is the result of a considerable amount of work on lead in amorphous materials, glasses, enamels and glazes. The reader will find here both the historical aspects and the scientific and technical aspects of the use of this highly controversial element.
Introduction
Patrice LEHUÉDÉ and Anne BOUQUILLON
C2RMF, IRCP, Paris, France
Glass is a material that has exerted fascination since its invention, due to its exceptional qualities: transparency, shine, coloration and its multiple technical applications. Since the second millennium BC, humans have used this material for increasingly varied purposes: prestigious adornment and decoration elements initially intended for the elites, then objects of everyday life such as window panes and stained glass, mosaics, ceramic decorations (glazes) and metal decorations (enamels).
The composition of vitreous materials may include a very large number of elements, therefore their physical and chemical properties may vary widely. Hence, the introduction in the first century BC of lead for glazes and even earlier for massive glass was a major technological and esthetic progress, which was our intention to highlight. The bibliography dedicated to the history of heritage glass, enamels and glazes is plethoric, as is that concerning the characteristics and properties of the material “glass”. On the other hand, the texts exclusively related to vitreous materials containing lead are much scarcer. This is why the first volume of the “Cultural and Industrial Heritage Materials” collection is dedicated to them. Its approach is strongly multidisciplinary, in an intent to offer the reader complementary perspectives. Lead glasses and glazes are at the intersection of several “industries” of the arts of fire: glass-makers, ceramists and metallurgists constitute an association of trades in which the discoveries made by some of them contribute to advancing the know-how and technologies of the others, in which the by-products of the activity of some are recovered and used by the others. The core of this book reviews the current knowledge on the intertwined history of these materials in various civilizations.
However, in our opinion, such a study cannot be approached in the absence of a precise idea of what a lead glass is and how it resists alterations over time.
The book we propose is therefore written by experts in the field of heritage sciences and material sciences. A first part briefly describes the advantages brought by lead in the glass-making matrix and the ensuing difficulties, as well as the contributions of isotopic analyses to the research of lead sources. This is followed by a more theoretical part related to the structure of lead glasses and its influence on glass color, particularly if it contains copper and iron. The third part focuses on the history of lead glass since its origin until present; it relies on the published ancient recipes and details the knowledge of Western medieval and Renaissance enamels and of Islamic lead glasses, whose significance can be better appreciated nowadays. The history of lead-glazed ceramics will be the object of a fourth part, with a specific review of the interactions between glaze and ceramic, on the one hand, and with the burial medium, on the other hand. Finally, considering the importance attached to environmental and public health problems associated with the use of lead, a fifth part will be dedicated to the interactions between lead glass and the liquid with which it is susceptible to get in contact, and to the standards that are nowadays applicable to the fabrication of these objects.
Our fullest gratitude goes to Philippe Sciau for his trust in us. We warmly thank Michel Dubus for our fruitful discussions and René Gy (SGR) and Alain Meunier (University of Poitiers) for having attentively read through certain parts of this book. We also thank the entire department of archives and new information technologies of C2RMF for their support.
PART 1Overview and Specific Techniques for the Analysis of Lead Glasses and Glaze
1Overview
Patrice LEHUÉDÉ
C2RMF, IRCP, Paris, France
Glass is often defined by contrast with crystal, as illustrated by the following definition formulated by Zarzycki (1982): “Glass is a non-crystallized solid that exhibits glass transition”1. This definition is however too restrictive for the heritage domain: many glasses involve in fact a crystallized phase, for example in the form of pigment or opacifier. It should therefore be considered as a glass a product that involves a significant glass phase and that has many points in common with glasses in the strict sense. The same difficulty arises for glazes, which certainly involve a significant glass phase, but may also include crystallized phases. Finally, the definition of lead glass is also debatable: modern instruments of characterization indicate the presence of lead in practically all glasses, often in minute traces. The fact that lead was deliberately added may be considered a criterion, which is difficult to prove, and it seemed to us that a 5% oxide weight threshold, as suggested by the researchers for the mosaic tesserae (Verità et al. 2009), was realistic, and we therefore adopted it.
1.1. Advantages brought by lead
The presence of lead is absolutely not essential for glass- or glaze-making, but in the history of glass a significant content (over 5% by weight of PbO) of lead can sometimes be found in silicate glasses, occasionally at least since 1500 BC (Turner 1956; Charleston 1960; Shortland and Eremin 2006) (Chapter 6).
Similarly, the first actual lead glazes (with high lead content) probably date from the Roman period (Tite et al. 1998). But a lead content above 5% can be found in certain glazes, partly in the form of lead antimonate Pb2Sb2O7, since 1500 BC (Mecking 2013; Molina et al. 2014) (Chapter 10).
The fact that the introduction of lead in the vitreous matrix for certain applications appeared as a necessity is justified by the specific properties it brings. This chapter gives an overview of these properties, some of which will be extensively developed in the following chapters.
1.1.1. Lead oxide as fluxing agent
Lead oxide acts as a very efficient fluxing agent in lead glasses, in the same way as, for example, Na2O or K2O or B2O3, allowing elaboration of glasses and glazes at relatively low temperature. The binary diagram PbO-SiO2 is a good illustration of this effect (see Figure 3.6): in the 60–100% molar PbO range, the mixture is fully molten for temperatures ranging between 700 and 800°C, which shows that the use of an additional fluxing agent is not necessary for glazes that are very rich in PbO for an implementation at a maximum temperature of about 1,000°C. The same does not apply for lower lead contents, for example those that can be observed in lead crystal glasses (25–33% PbO in oxide weight): it is important to add another fluxing agent such as K2O to be able to elaborate the glass at a reasonable temperature of less than 1,170°C (Geller and Bunting 1936). But even at lower concentration, the fluxing agent role of lead oxide is prominent. It also increases the dissolution rate of impurities such as the fragments of refractory materials, so that the quality of the resulting glass is better than with traditional fluxing agents such as Na2O (Leiser 1963; Shelby 2005, p. 125) and bubbles are more easily removed (Eppler and Eppler 2000, p. 215).
1.1.2. Influence of lead oxide on viscosity
PbO decreases the viscosity of glass, rendering it easier to process. Indeed, viscosity is the essential factor in all the glass hot forming processes, each process (blow-forming, fiber drawing, thermoforming, etc.) being optimized for a value of viscosity, and the obvious interest is to obtain this value of viscosity at a moderate temperature (Robertshaw et al. 2010, p. 369). Lead glasses are often qualified as “longer” than traditional soda-lime silica glasses, meaning that they have a lower viscosity variation rate with temperature (see Figure 1.1). This is an advantage, since forming is then less sensitive to temperature variation. However, similar to many other properties, viscosity depends on the overall composition of glass, and not only on its PbO and SiO2 contents. Consequently, accurate comparisons of the behavior of various glasses must integrate all their compounds, making them more difficult.
Figure 1.1.Variation of the logarithm of viscosity (in Pa·s) as a function of temperature (in °C). Solid line: lead crystal; dotted line: soda-lime silica glass of float type. Curves calculated using Fluegel modeling (Fluegel 2007)
The viscosity curve can be often estimated based on the composition of glass (see, for example, the works of Fluegel (2007)); unfortunately these works cover relatively few of the lead glasses and therefore they are less reliable for this type of glasses than, for example, for the soda-lime silica glasses.
1.1.3. Influence of lead oxide on the expansion coefficient
This influence is often of little interest for massive glasses, but it is essential for glazes. Indeed, during the cooling of a ceramic object covered with a glaze, if the expansion coefficient of the glaze is clearly different from that of the ceramic, stresses occur at the glaze/ceramic interface and they are often at the origin of the defects of the finished object: compression stresses that may lead to the burst of the glaze when the expansion coefficient of the glaze is lower than the one of the ceramic, extension stresses responsible for the appearance of cracks (crazing) in the opposite case. The generally admitted preference is for a glaze with an expansion coefficient that is slightly below that of ceramic by 5–15% (Tite et al. 1998). There are tables or even software for the calculation of the expansion coefficient of a glass based on its composition (Eppler and Eppler 2000, p. 251): they show that if Na2O is replaced by PbO in a glass composition, the expansion coefficient decreases (the contribution of PbO to the expansion coefficient is of about one-fifth of that of the Na2O for the same oxide weight concentration). The whole set of elements should however be taken into account in the estimation of the expansion coefficient. As the coefficient is normally above that of the ceramic, it is therefore interesting to use a lead glaze with low alkaline content in order to limit the crazing problems. Moreover, it is important to note that the presence of crystals in the glaze complicates particularly the estimation of the expansion coefficient based on the average composition, as well as the diffusion of elements of the glaze into the ceramic (or the opposite), or the volatilization of certain elements during the heat treatment.
1.1.4. Influence of lead oxide on surface energy
Bansal and Doremus (1986, p. 106, 111, 130) compiled the values of surface tension for many glass compositions. It systematically appears that the introduction of lead in the vitreous matrix clearly decreases its surface energy. This effect is explained by the high polarizability of Pb2+ ions (Scholze 1974, p. 224). The result is an easier wetting, which is a particularly interesting property in the case of glazes deposited on ceramic, since glaze adhesion is then better. Tite et al. (1998) gives 230 mJm−2 for a glaze with high lead content compared to 280 mJm−2 for an alkaline glaze. It is also this property that may explain the easier digestion of grains in the vitreous matrix containing lead. Lead presence also enhances the dispersion of opacifiers (Paynter and Jackson 2018). Finally, a lower surface energy has another advantage in the case of glazes: the latter have the natural tendency to form a smooth surface (Lehman 2002). Therefore, if the glaze contains bubbles, they tend to move up to the surface due to gravity and burst, leaving a hollow surface defect; this hollow, which significantly affects the aspect of the surface, is much easier smoothed down, at constant viscosity, if the surface energy of the glaze is low (Eppler and Eppler 2000, p. 216).
1.1.5. Influence of lead oxide on the color
The introduction of PbO in a colorless glass does not bring color as long as the content is moderate (crystal glass is renowned for its absence of color). But when the PbO content exceeds 30% mol, a yellow brown color may appear (Cohen et al. 1973), whose origin will be discussed in Chapter 4. On the other hand, the shade brought by certain coloring ions in solution in the glass may vary depending on the lead content of the matrix in which they are (Lehman 2002, p. 107). Hence, copper in the Cu2+ form gives a blue color to a soda-lime silica glass, of turquoise shade when the PbO content is below 40%, and emerald green when the lead content is higher (La Delfa et al. 2008) (Chapter 4).
Finally, some crystals such as lead antimonates Sb2O5·2PbO, lead stannates SnO2·2PbO and cuprite Cu2O bring by their own color a shade to the glass (yellow for the first ones, red for the last one) and play the role of pigment. It can be noted that when coloring is done with lead antimonate pigments, the overall analysis of the glaze or glass usually leads to a mean PbO concentration much higher than the value calculated by stoichiometry based on the concentration of Sb2O5: the PbO/Sb2O5 ratio is often 2 or 3, and even more, when the stoichiometric ratio is 1.38, which means that a part of the lead is in the vitreous matrix (Kaczmarczyk and Hedge 1983).
In the case of opaque red glasses that are colored using cuprite Cu2O crystals, for example those referred to as “sealing wax”, there are often significant contents of PbO (20 % or more in oxide weight) and it is admitted that the presence of PbO in the glass promotes the crystallization of cuprite (Barber et al. 2009, pp. 115–128) (Chapter 6).
A further advantage of lead glazes in terms of color is that since they are elaborated at relatively low temperature, certain pigments that are unstable at high temperature can be readily used, such as cadmium sulfoselenides (Eppler and Eppler 2000, p. 34).
1.1.6. Influence of lead oxide on devitrification
Glasses maintained at a temperature below TL2 and above TG tend to crystallize. The formation of such crystals utterly modifies the properties of the glass, and first of all their transparency. Glasses are always molten at a temperature above TL: during cooling (and forming), it is therefore essential to rapidly cross the critical temperature range between TL and TG. The nature of the crystals forming during devitrification depends on the composition of glass and on temperature (e.g. α and β wollastonite CaSiO3, diopside CaMgSi2O6 in the case of soda-lime silica glass) while the growth rate of these crystals depends on viscosity and therefore on temperature. This growth rate also varies significantly with the composition of glasses; hence when one part of the lime is replaced by magnesia in the composition of a soda-lime silica glass, the liquidus temperature deceases, but also the devitrification rate (Barton and Guillemet 2005, p. 77). The same applies for the introduction of lead into the composition (Nordyke 1984; Hynes and Jonson 1997, p. 137; Lehman 2002, p. 17; Barber et al. 2009). Lead crystal glasses (close to 8SiO2-K2O-PbO) have low sensitivity to devitrification, and the crystals that may form at the surface are silica, cristobalite and tridymite crystals, generated by a surface volatilization of lead (Volf 1984, p. 451). On the other hand, these glasses are not subjected to demixing (which is a separation of phases, similar to the case of devitrification, but the phase that precipitates is not crystallized), at least as long as the PbO content remains below 80% in oxide weight (see Chapter 3).
1.1.7. Influence of lead oxide on glass redox
In glasses and glazes, there are usually elements that are susceptible of being present under various degrees of oxidation. The most frequent is iron. It is responsible for a coloring that varies a lot depending on its oxidation state: Fe2+ or Fe3+. It is therefore very important to characterize this degree of oxidation; this is done using the glass “redox”, which is defined by Fe2+/Fetotal ratio. Hence, for the usual soda-lime silica glasses, the redox varies between 0.9 for the very reduced glasses and 0.1 for oxidized glasses (Chopinet et al. 2002). The redox depends on temperature (glasses elaborated at higher temperature are more reduced) (Chopinet et al. 2002) and on the atmosphere during glass elaboration, though reaching the equilibrium between glass and atmosphere may be a very lengthy process, especially when a large quantity of glass is elaborated. But redox also varies with glass composition. For soda-lime silica matrices, the higher the content of modifying cations, such as Na+ or Ca++, of the glass, the stronger the oxidation tendency at constant oxygen partial pressure (Chopinet et al. 2002). When glasses contain lead, the influence of lead content is poorly documented. It is admitted that lead addition tends to lower the Fe2+/Fe3+ ratio (Edwards et al. 1972), while increasing the Cu+/Cu2+ ratio (Edwards et al. 1972; Freestone 1987), which certainly explains why many red glasses colored by cuprite Cu2O crystals often have high lead content (see Chapter 6).
1.1.8. Influence of lead oxide on glass durability
It is generally admitted that lead glasses have better durability than soda-lime silica glasses. Nevertheless, since this durability depends on the set of present elements (and on their concentration), and on the testing conditions for assessing this durability (particularly the pH), the comparison between glass with lead and glass without lead is not very simple. It can nevertheless be stated that lead glasses have good durability for average pH. On the other hand, for acid pH, this durability is weakened (Bansal and Doremus 1986, p. 656; Lehman 2002, pp. 21–24) and may cause problems. This point will be developed further on (Chapters 13 and 14). Similarly, in alkaline medium, the durability of lead-rich glasses is lower than the one of classical soda-lime silica glasses (Bansal and Doremus 1986, p. 655).
1.1.9. Influence of lead oxide on glass density
Lead being a heavy element (compared to Si, Na, K or Ca), it is obvious that its introduction in a glass generates a net increase in density. Nevertheless, this increase is not very high for moderate contents; hence a lead crystal (25% by weight of PbO) has a density of 2.9, compared to 2.5 for a classical soda-lime silica glass, and it is not very easy to determine if an object is made from crystal or not just by weighing it. For much higher lead contents, the density difference then becomes very large compared to that of a classical soda-lime silica glass, which makes them easier to distinguish. Curves giving the variation of density of lead glasses depending on the lead content (see Figure 1.2), or more recently based on measurements on glasses of the PbO–SiO2 system (Ben Kacem et al. 2017), are available.
Figure 1.2.Variation of the density of lead glasses as a function of PbO content according to Davison (2003, p. 10)
1.1.10. Influence of lead oxide on optical properties
Just as the addition of lead to a glass increases its density, it also increases its refractive index, as well as its optical dispersion. This property is obviously widely used in optical glasses, as it is then possible to adjust the refractive index of a glass by varying its lead content. The composition-refractive index relation was the object of many works since the pioneering works of SCHOTT in the 1880s (Marker and Neuroth 1998), but this relation is however not simple, and various formulas were proposed (see the synthesis in Scholze (1974, pp. 123–133)). The lead content of a glass has a strong influence on the refractive index nD (see, for example, Figure 1.3).
Figure 1.3.Relation between the optical index nD of glasses and their lead content according to Nordyke data (Nordyke 1984, p. 25)
According to the classical distinction, there are crown glasses3 with a low refractive index and a high Abbe number, and flint glasses4, which by contrast, have a high refractive index and a low Abbe number. It is important to recall that dispersion corresponds to the variation of the refractive index with the wavelength, and that the relation between the Abbe number (νD) and this dispersion is:
where nD is the refractive index of glass for λ = 0.6563 μm, nF is the refractive index of glass for λ = 0.4861 μm and nC is the refractive index of glass for λ = 0.5893 μm.
The higher the Abbe number, the weaker the glass dispersion of the various wavelengths. The Abbe number and the refractive index of a large number of glasses used in optics are often represented in a diagram. The example provided here refers to lead glasses (see Figure 1.4).
Figure 1.4.Abbe diagram giving the refractive index nD of various glasses depending on their Abbe number νD for various flint glasses containing lead (according to the values of the SCHOTT catalogue for optical glasses (SCHOTT 2020))
Moreover, the increase in the refractive index of a glass makes it possible to increase the intensity reflected by the air–glass interface. For normal incidence, the reflected light intensity by such an interface is in fact (n − 1)2/(n + 1)2. But the higher the light intensity, the “brighter” the glass appears. Thus, when comparing a classical soda-lime glass (index n = 1.51) to a classical lead crystal (n = 1.55), the intensity reflected by the surface passes from 4.1% to 4.65%. This is a small increase, which is difficult to perceive by the eye, especially as the alteration of ancient objects tends to decrease the optical index of the surface and increase the rugosity, the object becoming less bright. On the other hand, for glazes whose PbO content may reach 70% by oxide weight, and whose index is practically 1.80, the effect is very clear: the intensity reflected by the surface is then 8.14%. It is interesting to note that rock crystal (quartz) has an index of 1.55; it has long been considered as a reference in terms of optical quality of the objects. The glass developed by the Venetians in the 15th century for manufacturing luxury objects is referred to as “cristallo” (Verità 1991, pp. 57–67) because it imitates rock crystal. This glass does not contain lead and therefore its index is of the order of 1.5.
1.1.11. Influence of lead oxide on the mechanical properties
Glass is an elastic material at ambient temperature. It is therefore characterized by a modulus of elasticity that connects the applied stress to the deformation. The modulus is all the higher as the elongation is weaker when the glass is subjected to tensile stress. The value of this modulus depends on the composition of the glass. The introduction of lead in the composition of a glass reduces the modulus of elasticity (by about 15–20% compared to a classical soda-lime silica glass) and also the hardness (Volf 1984, p. 458; Hynes and Jonson 1997). Consequently, the lead glass cutting and grinding is easier and the tool wear is lower than in the case of classical soda-lime silica glasses. Similarly, mechanical polishing is easier. It is however important to note that glass polishing is a complex phenomenon that involves both the physical properties of glass (its modulus of elasticity, its hardness) and chemical reactions at the glass/polishing paste interface (Cook 1990). It is therefore difficult to predict the behavior of a glass only based on its composition, but empirical measurements, following standardized tests, show that lead glasses tend to be more rapidly polished, which is widely taken advantage of in the industry of cut lead crystal glass.
It can also be noted that the resistance to cracking is much lower than in the case of lead glasses (Kato et al. 2010): consequently, if these glasses are submitted to an impact, they are more easily damaged with the development of cracks: they appear more fragile to scratch.
A crystal drinking glass can be easily distinguished from a soda-lime silica one by the specific sound it emits when tapped or when a wet finger is run on it. The vibration frequency of the sound waves depends on the geometry of the object, but also on the wave propagation velocity through matter. This velocity is lower in the lead crystal than in the soda-lime silica glass, because of its higher density and its lower Young’s modulus. On the other hand, the sound wave is far less damped in the crystal glass: the sound “lasts” longer. The damping of sound waves is due to internal friction, which is weaker for crystal glass. It should be noted that the crystal sound is not so readily perceptible when the glass is thick. The sound properties of crystal were used by musicians (among them Mozart) to create pieces of music for instruments such as glass harmonica and the Cristal Baschet.
1.1.12. Influence of lead content on the absorption of ionizing radiation
It is a well-known fact that lead strongly absorbs ionizing radiation (X and gamma rays), which explains its use in the protection against this type of radiation. Lead-rich glasses can be used for making transparent windows while giving a radiation protection. These glasses may reach 71% by mass of PbO (Sovis 2020) and even 81% (Nordyke 1984, p. 9). The intensity of X-rays that is not absorbed by the material is given by:
with:
I = intensity of radiation that crosses the material;
I
0
= initial intensity;
μ/ρ = mass attenuation coefficient of the material for the given radiation;
ρ = density of the material;
x = thickness of the material through which the radiation passes.
But μ/ρ is much higher in the case of lead than in the case of lighter elements (typically silicon) for radiation of energy below 200 keV. As, on the other hand, the density of lead-rich glasses is also significantly higher than that of soda-lime silica, it is not surprising that lead glasses are used as protection against ionizing radiation.
These properties of lead concerning the absorption of ionizing radiation have also been used for manufacturing cathode ray tubes and television tubes: the protection against X-rays is obviously essential, and, on the other hand, the influence of lead on glass viscosity facilitates the fabrication of these objects of complex shape.
1.1.13. Miscellanea
Lead glasses are known for having very low electrical conductivity: Pb2+ ion is relatively large (0.132 nm) and prevents the movement of alkaline ions, commonly responsible for electrical conduction in glasses. This property is useful for applications in lighting, cathode-ray tubes and electronics (Schoenung 2008).
On the other hand, the fact of having available a low viscosity glass, which moreover has a good adhesion to metals that serve as electrode, renders the lead glass very useful for welding, thus opening the way for applications in the field of electronics and cathode-ray tubes (Nordyke 1984, p. 33; Pfaender 1996, p. 138).
1.2. Difficulties related to the use of lead oxide
1.2.1. Elaboration difficulties
Despite the advantages resulting from the addition of lead to glass compositions, it was not before the end of the17th century that the large-scale development of lead glasses started. It is worth considering why. It is most certainly largely due to the fact that mastering the melting of this type of glass raised problems. The use of lead glasses was already widespread before those times, but only for small-scale manufacturing (Mecking 2013, p. 2; Velde 2013, p. 75): small-size objects or small-series objects, glazes, which did not require the elaboration of large amounts of glass. Indeed, the lead oxide in this type of glass is susceptible to be reduced quite readily to metallic lead under the action of a reducing agent. It may be a matter of particles of metallic iron accidentally introduced in the composition, or of carbon particles resulting from incomplete combustion when using open crucibles or any other reducer or even the action of the flame itself (Wang et al. 2004). These particles of metallic lead fall at the bottom of the crucible (Volf 1984, p. 452) and attack the refractory (Neri et al. 1752) or the platinum of the crucible, which may lead to the puncture of the pot: the glass then spreads on the ground. The result is a loss all the greater as the pot size is larger, without counting the risks related to the sudden presence of melting glass on the ground. This phenomenon of refractory puncture by the metallic lead is well known to today’s glassmakers using household cullet resulting from the collection of glass to be recycled: several furnaces were punctured this way, suddenly releasing dozens of tons of glass at 1,400°C (in this case the origin of lead is attributed to the recycling of champagne bottles whose neck was protected by a lead-rich metallic film). The solution found in the 17th century was the introduction in the composition of a powerful oxidizer (potassium nitrate or saltpeter) and perhaps the use of closed pots (Watts1990) (Chapters 6 and 7).
1.2.2. Public health problems
The risks associated with the use of lead (lead poisoning) have been known for a long time, as they were signaled by Hippocrates and then by Pliny (Hynes and Jonson 1997). Lead acts mainly by ingestion and by inhalation. It has powerful neurological effects. But it was only starting with the beginning of the 20th century that the risks related to its use have been thoroughly evaluated, and increasingly strict safety rules have been implemented in the glass and ceramic plants using lead (Singer and Germain 1960; Eppler 1983). These rules concern first of all the choice of raw materials in order to minimize dusts, especially those having a certain solubility in acid medium, and the volatile compounds of lead during the elaboration of glasses: a temperature of elaboration of lead glazes below 1,170°C is recommended in order to limit this volatilization (Lehman 2002). It is important to note that as soon as lead enters in the vitreous matrix, considered as inert, it is far less susceptible to be released, except for specific use cases, for example if the glass in which it is integrated comes into contact with an acid solution. It was not until the 1970s that this risk was taken into account and reflected by the adoption of very strict rules (Ben Kacem 2017) (Chapters 13 and 14).
Finally, besides the health problems related to lead as such, a further risk may occur. Indeed, lead glasses are generally refined using arsenic in the form of As2O3 or antimony in the form of Sb2O3, associated with an oxidizer, generally potassium nitrate KNO3 (Chopinet et al. 2002), as the classical pair sulfate/reducer can no longer be used. But arsenic and antimony are themselves extremely toxic.
1.3. Conclusion
It can be noted that the introduction of lead in the composition of glass or glaze adds many interesting properties. However, the difficulties related to its use for significant productions were not properly addressed until the end of the 17th century, and the related public health problems have already practically stalled its use for glazes and limited it for lead glasses.
1.4. References
Bansal, N.P. and Doremus, R.H. (1986).
Handbook of Glass Properties
. Academic Press, New York.
Barber, D.J., Freestone, I.C., Moulding, K.M. (2009). Ancient copper red glasses: Investigation and analysis by microbeam techniques. In
From Mine to Microscope
, Shortland, A.J., Freestone, I.C., Rehren, T. (eds). Oxbow Books, Oxford.
Barton, J. and Guillemet, C. (2005).
Le Verre, science et technologie
. EDP Sciences, Les Ulis.
