Metal Soaps in Art: Conservation and Research

Abstract

This go-to reference work surveys the current state of knowledge in the field of metal soap-related degradation phenomena in art works. It contains detailed descriptions and images of the different phenomena and addresses the practical aspects of soap formation, preventive conservation, and treatment. The occurrence of metal soaps is one of the defining issues in the conservation of painted surfaces, and one that presently leaves innumerable open questions. It is estimated that around 70% of paintings in museum collections are affected by some form of metal soap-related degradation. In recent years, significant advances have been made in the detection and characterization of these compounds through interdisciplinary approaches including conventional spectroscopy and microscopy as well as emerging synchrotron-based techniques. This book for the first time captures a panoramic overview of the state of knowledge of metal soaps related to both scientific analysis and implications for conservation and treatment. It also critically examines open questions. The book is accessible to audiences with varied backgrounds (e.g. conservators, students of conservation science) while simultaneously presenting the technical details indispensable for academics and researchers active in this field. Intro; Foreword; Preface; Contents; Contributors; About the Editors; 1 A Brief History of Metal Soaps in Paintings from a Conservation Perspective; 1.1 Introduction; 1.2 Past History; 1.3 Lead Soap Aggregates; 1.3.1 International Survey; 1.4 Other Lead Soap Manifestations; 1.5 Zinc, Potassium, Calcium, Copper, and Aluminum Soap Manifestations; 1.6 Time Frame; 1.7 Conservation Perspectives; 1.8 Outlook; References; Part I Formation, Migration and Environmental Influences; 2 Zinc Soaps: An Overview of Zinc Oxide Reactivity and Consequences of Soap Formation in Oil-Based Paintings 2.1 Introduction2.2 Zinc Oxide; 2.3 Fatty Acid Composition in Oil Mediums; 2.4 FTIR Characterization of Zinc Soaps; 2.5 Morphology Change; 2.6 Zinc White Paints with Added Stearates; 2.7 Formation of Crystalline Zinc Soaps; 2.8 Zinc Soaps and Paint Cleavage; 2.9 Zinc Soap Aggregates; 2.10 Mineralized Zinc Soap Aggregates; 2.11 Zinc Salt Formation and Surface Bloom; 2.12 Environmental Influences; 2.13 Conclusion; References; 3 Toward a Complete Molecular Model for the Formation of Metal Soaps in Oil Paints; 3.1 Introduction; 3.2 Oil Paint Drying: The Formation of Ionomer Networks 3.2.1 Carboxylate Formation During Oil Paint Drying3.2.2 Migration of Metal Ions Throughout the Polymeric Medium; 3.2.3 Formation of Ionomer-Like Binding Medium; 3.3 Oil Paint Deterioration: Metal Soap Formation in Ionomer Networks; 3.3.1 Free Fatty Acid Generation Through Ester Bond Hydrolysis; 3.3.2 The Crystallization of Metal Soaps; 3.4 Outlook; 3.5 Conclusions; References; 4 Understanding the Dynamics and Structure of Lead Soaps in Oil Paintings Using Multinuclear NMR; 4.1 Introduction; 4.2 Materials and Methods; 4.2.1 Synthesis of Materials; 4.2.2 NMR Methods; 4.2.3 Fitting Methods 4.2.4 Reaction of Samples at Different Relative Humidities4.3 Results; 4.3.1 Structure of Lead Soaps; 4.3.2 Local Molecular Dynamics of Soaps; 4.3.3 Kinetics of Soap Formation; 4.4 Conclusions; References; 5 Historical Evolutions of Lead-Fat/Oil Formula from Antiquity to Modern Times in a Set of European Pharmaceutical and Painting Treatises; 5.1 Introduction; 5.1.1 Pharmaceutical Domain; 5.1.2 Paint Domain; 5.2 Text Corpus; 5.2.1 Pharmaceutical Treatises; 5.2.2 Painting Treatises; 5.3 Choice of Ingredients and Proportions; 5.3.1 Lead-Based Ingredients; 5.3.1.1 Pharmaceutical Domain 5.3.1.2 Paint Domain5.3.2 Fat Ingredients; 5.3.2.1 Pharmaceutical Domain; 5.3.2.2 Paint Domain; 5.3.3 Proportions of Lead and Fat/Oil Compounds; 5.3.3.1 Pharmaceutical Domain; 5.3.3.2 Paint Domain; 5.4 Controlling the Operating Conditions: Use of Fire, Water, and Sunlight and the Grinding Level of Lead-Based Compounds; 5.4.1 Use of Fire and Control of the Temperature by the Use of Water; 5.4.1.1 Pharmaceutical Domain; 5.4.1.2 Paint Domain; 5.4.2 Use of Sunlight; 5.5 Conclusions; References; 6 Impact of Lead Soaps on the Formation of Age Craquelure; 6.1 Introduction; 6.2 Results and Discussion