Fiat Lux: Climatic Considerations in Medieval Stained Glass Aesthetics
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Fiat lux: climatic considerations in medieval stained glass aesthetics By Christopher Thomas Simmons Department of Atmospheric and Oceanic Sciences McGill University, Montréal August 2008 A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements of the degree of Master of Science ©Christopher Thomas Simmons, August 2008 Abstract As expressions of regional architecture built to last, sacred Gothic structures often possess several adaptations to their prevailing climate regime. However, the late medieval period in Europe is also marked by a transition to cooler and likely cloudier conditions. It is within the context of this climate change that we consider one of the most important considerations in Gothic churches—interior daylighting—during the transition from the Medieval Warm Period to the Little Ice Age. This thesis seeks to determine whether increasingly cloudy conditions over northern continental Europe may have influenced the use of more white glass in the Fourteenth century. With primary illuminance and luminance data collected in Europe, the results indicate that full-colour programs appear to perform best under sunny conditions, whereas later, white-dominated programs provide similar illumination under cloudy conditions. However, this high-translucency glazing is associated with limited lighting gains and major aesthetic drawbacks under sunny conditions. Résumé Etant donné que les cathédrales gothiques ont été construites pour durer, plusieurs adaptations aux climats regionaux y ont été apportées. Cependant, la fin du Moyen Âge fut marquée par un changement climatique vers des conditions plus froides et probablement plus nuageuses en Europe du nord continentale. C’est donc dans ce contexte que nous cherchons à comprendre l’un des éléments les plus importants de l’architecture gothique—éclairage naturel intérieur—durant la transition entre la période chaude médiévale et le petit âge glaciaire. En particulier, cette thèse voudrait évaluer la relation entre l’utilisation de plus en plus fréquente du vitrail blanc durant le XIVème siècle d'un côté et le changement climatique d'un autre côté. Avec des données d’éclairement lumineux et de luminance lumineuse collectées dans plusieurs cathédrales en Europe, les résultats indiquent que les vitraux plein-colorés éclairent mieux l’interieur durant les journées ensoleillées. D'autre part, les vitraux incolorés du XIVème siècle fournissent un éclairage similaire durant les journées nuageuses, toutefois ils ne présentent que peu d’avantages dans des conditions plus ensoleillées, de plus l’utilisation du vitrail plus transparent produit des effets négatifs sur le plan esthétique. i Table of Contents Abstract i Table of Contents ii Acknowledgements v 1 Introduction 1 1.1 Sacred Architecture as an Indicator of Climatic Change . 3 1.2 Interior Lighting Strategy and Window Sizes from the Periods Romanesque to Gothic . 4 1.3 The Relationships between Window Size and Glazing Material in the Interior Illumination of Romanesque and Gothic Structures . 6 1.4 Stained Glass, Illumination, and Climate . .9 2 Evidence of a Transition to Cloudier Conditions in Northern Continental Europe between the Twelfth and Fifteenth Centuries 13 2.1 Explicit Cloudiness Proxies: Comets, Marine Cores, and Galactic Cosmic Rays . 13 2.1.1 Comet Sightings 13 2.1.2 Planktonic Illumination Indicators 14 2.1.3 Galactic Cosmic Rays 15 2.2 Precipitation Proxies . .17 2.2.1 Peat Bogs: Warm Season Effective Precipitation 17 2.2.2 Speleothems: Stable Isotope Records and Annual Banding 21 2.2.3 Tree Ring Reconstructions 24 2.3 The NAO: Winter Cloudiness Variability . .25 2.3.1 NAO and Cloud Cover Relationships 26 2.3.2 NAO Proxies and Related Indicators 30 Chapter 2 Tables and Figures . 35 ii 3 Data and Methodology 40 3.1 Site Selection . 40 3.2 Cathedral Interior Illuminance Analysis Methods . 41 3.3 Exterior Illuminance Analysis Methods . 43 3.3.1 Procedures and Daylight Factor Calculations 43 3.3.2 Validation Experiments 46 3.3.3. HDF and VDF-Based Horizontal Illuminance Prediction Algorithm 47 3.4 Interior Luminance Analysis Methods . 48 4 Results 52 4.1 Coloured Programs of the Thirteenth Century . 52 4.1.1 Chartres Nave: An Expression of Thirteenth Century Architectural Lighting 52 4.1.2 Strasbourg Cathedral: A Full-Colour Nave in the Holy Roman Empire 57 4.1.3 Bourges: A Full-Colour Ambulatory 61 4.1.4 Le Mans: A Full-Colour, Rayonnant Choir 67 4.2 The Grisaille Revolution . 72 4.2.1 Tours and Cologne: The Effect of Grisailles on Choir Illumination 74 4.2.2 The Formalist Approach: The Effect of Grisailles on Architectural Lighting 76 4.2.3 The Effects of Backlighting on Grisailled Interiors under Sunny Conditions 85 4.2.4 The Ambulatory of Chartres: The Incorporation of Later Grisailles into a Full-Colour Program 89 4.3 Late Gothic Interiors: The Fourteenth through Sixteenth Century . .94 4.3.1 Évreux Ambulatory and Choir: The Grisaille-Dominated Interior 94 iii 4.3.2 The City Church: St-Serevin in Paris, St-Pantaléon in Troyes, and St-Nicolas in Troyes 97 4.3.3: Troyes Cathedral Nave 99 4.3.4 The Abbey Church of St-Ouen 103 4.4 Mediterranean Interiors . 105 4.4.1 Toledo, Sevilla, and Segovia 106 4.4.2 León 108 4.4.3 Santa Maria del Mar 110 4.5 Differential Relative Transmissivities . 111 Chapter 4 Figures . 118 Chapter 4 Tables . 140 5 Conclusions and Future Work 142 5.1 Conclusions . 142 5.2 Prospects for Future Work in Cathedral Lighting . 145 5.3 Chapter 5 Tables . 149 Appendix I: Glossary of Architectural and Fenestration Terms 150 References 154 iv Acknowledgements This research has been largely supported through the Richard H. Tomlinson Fellowship, which has made a multidisciplinary effort such as this possible. Dr. Lawrence A. Mysak, Professor of Atmospheric and Oceanic Sciences, is warmly thanked for his supervisory role on this project. The financial support through a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grant awarded to Professor Mysak is also gratefully acknowledged. In addition, I would like to thank Dr. Jennifer Veitch, Dr. Chantal Arsenault, Dr. Duygu Cetegen, and others from the National Research Council of Canada’s Indoor Lighting Division (Ottawa) for their close advisory role in the technical execution of this research. Dr. Christoph Reinhart, Harvard University, and Professor David Covo, McGill University, are also warmly thanked for advice given on the evaluation of architectural lighting performance. For support on climate issues, I would like to thank Ryan Eastman, University of Washington, for providing his cloud cover correlations data. Perhaps most importantly, I would also like to acknowledge Teresa Simmons, Robert Simmons, and Cathérine Thauer, my volunteer assistants without whose help little of this research would have been possible. In addition, I sincerely thank Rabah Aider, Veronique Meunier, Jasmine Rémillard, David Carozza, Andrés Antico, Alexandra Jahn, Cathérine Thauer, and Jan Sedlaček for their assistance in my multilingual correspondence with European government officials for the facilitation of this research. v 1 Introduction Shelters have always been integral elements of human society; people have relied on them since prehistoric times to provide vital protection from the outside world. Of all the physical external realities with which humans are concerned, weather and climate are perhaps the most fundamental considerations that go into the construction of shelters. We, as culturally adaptive creatures, have the remarkable ability to build shelters that enable us to live on virtually any region of the earth where food and water are obtainable. People familiar with a given region are often able to devise creative and effective adaptations to their native climates, and these are often seen through the lens of architecture. An often-cited example are the Mediterranean villas of Italy, from the Roman epoch to the Early Modern era, which are suited for dry, sunny climates. For instance, the location and size of villa windows are often strictly controlled to prevent excessive internal heating during the hot summers, and they are frequently designed around fountain courtyards, which provide a cool microclimate dominated by evaporative cooling and act as a relief from intense summer heat. Modern architecture, with its more durable, weather-resistant plastic, metal, and glass materials (and accompanied by the conveniences of modern electrical and heating and cooling systems), has become more global and has diverged from the vernacular prototypes of the past. However, even today local climatic concerns, such as balancing thermal and psychological comfort with daylight energy savings for a given location, are a high priority in the design of any building. Therefore, the small, gradual regional climate transitions associated with global warming can pose significant challenges to modern architects, as discussed extensively in Roaf (2005). The overarching goal of our research is to examine the vernacular architectural styles of the pre-modern era in order to illustrate the interactive relationship between architecture, as functional shelter design, and the prevailing regional climate. In addition, we hope to demonstrate the modifications these vernacular architectural styles undergo in the face of natural climate change, both as a testament to potential past architectural concerns and the potential wide impacts to architectural design that today’s more anthropogenically-driven climate