Lifetime of Colour Photographs in Mixed Archival Collections
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UCL Bartlett School of Graduate Studies Centre for Sustainable Heritage Doctoral Thesis Lifetime of Colour Photographs in Mixed Archival Collections by Ann Fenech in collaboration with The National Archives 2011 To my family. I, Ann Fenech, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indi- cated in the thesis. Ann Fenech Abstract Chromogenic prints, which make up around 99% of all colour photographs, are amongst the most vulnerable materials in archival storage. However, although en- vironmental standards for storage are available, antagonistic requirements within archives mean that the recommended conditions are not always appropriate. This study evaluated the impact of mixed archival storage on chromogenic prints by fol- lowing three lines of research: environmental, material and values. During storage, three environmental parameters predominantly influence chro- mogenic print lifetime: temperature, relative humidity (RH) and pollutants. The pollutant of greatest interest was determined to be acetic acid as it is the most abundant pollutant within archival boxes and also causes greatest changes in dye concentrations. Materials research focussed on the development of two non-destructive analytical methods. The first used the sRGB colour model for monitoring dye concentrations. The second combined near infrared spectroscopy to develop applications for dating and stability prediction of chromogenic prints. The third line of research related to values, specifically fitness-for-purpose of an image within the context of an archival collection. A psychophysical approach was taken to determine the point at which colour changes are no longer accept- able, defined as the unacceptability threshold. It was identified that while assessor characteristics did not affect the threshold, image characteristics, particularly fading profile and image detail, did. Having investigated the three lines of research separately, their integration led to a more holistic approach. Accelerated degradation experiments were planned using design-of-experiment principles to develop a multiparametric dose-response function. The function relates the rate of degradation to temperature, RH and acetic acid concentration. This allowed for isoperms and isochrones, which connect 4 points of equal permanence and lifetime respectively, to be developed. Finally, an innovative photographic lifetime calculator has been developed using principles of stock modelling and the developed damage function, thus incorporating material and value change dependent upon environmental parameters. Contents Abstract 4 Contents 6 List of Figures 11 List of Tables 14 List of Definitions 16 List of Symbols and Abbreviations 18 Acknowledgements 21 1 Scope of Work 22 1.1 Introduction................................ 22 1.2 Research Questions . 24 1.3 Aims and Objectives . 24 1.4 ThesisOrganisation............................ 25 2 Colour Photography & the Chromogenic Print 27 2.1 Brief History of Colour Photography . 27 2.1.1 CapturingColourImages. 28 2.1.1.1 Additive Processes . 28 2.1.1.2 Subtractive Processes . 30 2.1.2 Commercial Processes . 31 2.1.2.1 ChromogenicColourPhotographs. 32 2.2 TheChromogenicPrint. .. 32 6 Contents 7 2.2.1 PhotographicPrintSupports. 33 2.2.1.1 BarytaPaper ...................... 35 2.2.1.2 Resin-Coated Paper . 36 2.2.2 Development of Chromogenic Images . 39 2.2.2.1 FormationoftheLatentImage . 39 2.2.2.2 DyeFormation . 41 2.2.2.3 Post Development Processing . 44 2.2.3 PhotographicDyeComponents . 45 2.2.3.1 DevelopingAgents . 47 2.2.3.2 CouplingAgents . 50 2.3 The Research Collection . 54 2.3.1 Methodology ........................... 54 2.3.2 Results and Discussion . 54 2.4 Conclusion................................. 56 3 Environmental Research 59 3.1 Colour Photographs & their Storage Environment . 59 3.2 TemperatureandRelativeHumidity . 62 3.2.1 Temperature............................ 62 3.2.2 Humidity ............................. 62 3.2.3 Relationship between Temperature and Relative Humidity . 63 3.2.4 MonitoringatTheNationalArchives . 64 3.3 Pollution Monitoring at The National Archives . 66 3.3.1 Methodology ........................... 68 3.3.1.1 LocationsMonitored . 69 3.3.1.2 Monitoring Outdoor-Generated Pollutants . 69 3.3.1.3 MonitoringoftVOCs. 70 3.3.1.4 MonitoringVolatileAldehydes. 70 3.3.1.5 Monitoring of Acetic Acid . 72 3.3.2 Results............................... 73 3.3.2.1 Outdoor-Generated Pollutants . 73 3.3.2.2 tVOCs.......................... 74 3.3.2.3 VolatileAldehydes . 76 3.3.2.4 Acetic Acid . 76 Contents 8 3.3.3 Discussion............................. 76 3.3.3.1 Monitoring the External Environment . 77 3.3.3.2 Monitoring of the Repository Environment . 80 3.3.3.3 Pollutant Concentrations Inside Archival Boxes . 83 3.3.3.4 Comparison of Pollutant Concentrations across the Locations ........................ 84 3.4 Conclusion................................. 85 4 Materials Research 87 4.1 MonitoringDyeConcentrations . 88 4.1.1 Methodology ........................... 90 4.1.1.1 Samples ......................... 90 4.1.1.2 Colorimetry. 91 4.1.1.3 ChromatographicAnalysis . 91 4.1.2 Results and Discussion . 92 4.1.2.1 Chromatographic Method Development . 93 4.1.2.2 Comparison of Chromatographic and Colorimetric Data........................... 96 4.2 DatingofPhotographs . 99 4.2.1 Methodology ...........................103 4.2.1.1 Samples .........................103 4.2.1.2 NIR Spectroscopy . 103 4.2.1.3 Chemometric Analysis . 103 4.2.2 Results and Discussion . 103 4.3 Conclusion.................................105 5 Values Research 108 5.1 ValuesandHeritage. .108 5.1.1 Anthropological/Ethnographical Approach . 109 5.1.2 EconomicApproach . .110 5.1.3 Overview .............................110 5.2 End-of-Lifetime of Chromogenic Prints . 111 5.2.1 Methodology ...........................115 5.2.1.1 ImagePreparation . .115 5.2.1.2 Assessor Questionnaire . 116 Contents 9 5.2.1.3 WorkshopParticipants . 118 5.2.1.4 Fitness-for-Purpose Assessment Workshops . 119 5.2.1.5 DataAnalysis. .120 5.2.2 Results & Discussion . 122 5.2.2.1 Influence of Assessor on Unacceptability Threshold . 122 5.2.2.2 Influence of Image Characteristics on Unacceptabil- ityThreshold ......................124 5.3 Conclusion.................................129 6 Integration of Research Lines 132 6.1 ImageDegradation . .132 6.1.1 Accelerated Degradation . 133 6.2 Effect of Pollutants on Chromogenic Prints . 135 6.2.1 Methodology ...........................136 6.2.1.1 DegradationExperiments . 136 6.2.1.2 Colorimetry. .137 6.2.1.3 DataAnalysis. .137 6.2.2 Results and Discussion . 138 6.3 Multiparametric Dose-Response Function . 142 6.3.1 Methodology ...........................144 6.3.1.1 Experimental Design . 144 6.3.1.2 Samples and Apparatus Set-Up . 145 6.3.1.3 DataAnalysis. .146 6.3.1.4 DOEAnalysis. .146 6.3.2 Results and Discussion . 147 6.3.2.1 Isoperms and Isochrones . 151 6.4 Effect of Hypoxia on Chromogenic Prints . 154 6.4.1 Methodology ...........................154 6.4.2 Results and Discussion . 154 6.5 Conclusion.................................156 7 Collection Modelling 158 7.1 Non-Destructive Survey Tool . 159 7.1.1 Methodology ...........................159 7.1.1.1 StabilityData. .159 Contents 10 7.1.1.2 NIR/MVA Analysis . 160 7.1.2 Results and Discussion . 160 7.1.2.1 AnalysisofStabilityData . 160 7.1.2.2 Predicting Stability using NIR/MVA . 161 7.2 Photographic Lifetime Calculator . 162 7.2.1 Methodology ...........................166 7.2.1.1 Input ..........................166 7.2.1.2 Process .........................166 7.2.1.3 Photographic Lifetime Modelling Tool . 166 7.2.2 Results and Discussion . 167 7.2.2.1 Case Study: The National Archives . 168 7.3 Conclusion.................................171 8 Conclusion and Further Work 173 8.1 Summary .................................176 8.2 FurtherWork ...............................178 Bibliography 181 A Publications and Conference Papers 203 A.1 Publications................................203 A.2 OralPresentations ............................204 B Conversion between Colour Spaces 205 B.1 Converting Lab to XYZ . 205 B.1.1 Finding fx, f y, f z .........................205 B.1.2 Finding xr, y r, z r .........................205 B.1.3 Finding XY Z ...........................206 B.2 Converting XYZ to sRGB . 206 B.2.1 Finding rgb ............................206 B.2.2 FindingsRGB...........................206 C The Fitness-for-Purpose Assessment Workshop Materials 208 List of Figures 2.1 Tree structure describing colour photographic processes. 29 2.2 The superimposed image of the first permanent colour photograph. 30 2.3 Photomicrograph of a Lumi`ere plate with the silver layer removed. 31 2.4 The relationship of colours used in photography. 33 2.5 The main components of a chromogenic photographic image and the relevant sections where they are discussed. 34 2.6 The backscatter ESEM image of a cross-section of modern fibre-based, B&Wphotographicpaper. 35 2.7 Schematic cross-section of an RC paper. 37 2.8 Cross-sectional diagram of a contemporary colour paper on resin-coated paperbase. .................................. 40 2.9 Kodacolor (1947) paper and Supra Endura (2008) paper showing the emulsionlayerorder. ............................. 41 2.10 First oxidation step of the developing agent. 43 2.11 Second oxidation step of the developing agent. 43 2.12 Productionoftheleucodye. 43 2.13 Oxidation of a leuco dye to an azomethine dye. 44 2.14