Non-Destructive Condition Assessment of Painting Canvases Using NIR Spectrometry
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Non-destructive condition assessment of painting canvases using NIR spectrometry Marta Oriola Folch ADVERTIMENT. La consulta d’aquesta tesi queda condicionada a l’acceptació de les següents condicions d'ús: La difusió d’aquesta tesi per mitjà del servei TDX (www.tdx.cat) i a través del Dipòsit Digital de la UB (diposit.ub.edu) ha estat autoritzada pels titulars dels drets de propietat intel·lectual únicament per a usos privats emmarcats en activitats d’investigació i docència. No s’autoritza la seva reproducció amb finalitats de lucre ni la seva difusió i posada a disposició des d’un lloc aliè al servei TDX ni al Dipòsit Digital de la UB. No s’autoritza la presentació del seu contingut en una finestra o marc aliè a TDX o al Dipòsit Digital de la UB (framing). Aquesta reserva de drets afecta tant al resum de presentació de la tesi com als seus continguts. En la utilització o cita de parts de la tesi és obligat indicar el nom de la persona autora. ADVERTENCIA. 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Faculty of Fine Arts Painting Department Conservation Section PhD program: Painting in the digital times: Afinity and specificity Years 2003-2005 Non-destructive condition assessment of painting canvases using NIR spectrometry A thesis submitted by Marta Oriola i Folch for the degree of PhD with a European mention Thesis director: Dr. Gema Campo Francés Barcelona, December 2011 To my family and to all the good friends and colleagues I am lucky to count with. Contents ABREVIATIONS USED………………………………………………………...…………………..…… 1 INTRODUCTION….…………………………………..…………..………………..……………...………. 3 1. The canvas support in paintings………………………………………………. 9 1.1 - Textiles used as a painting support…………………………………………………………….. 9 1.1.1 - The first textiles………………………………………………………………………………... 9 1.1.2 - Painting on canvas……………………………………………………………………………. 11 1.1.3 - Types of fibres used for paintings……………………………….. ………………………….. 15 1.2 - Cellulose: The main component of plant fibres ……………………………………………….. 20 1.2.1- Glucose……………………………………………………………………………………...….. 21 1.2.2- Glycosidic bond………………………………………………………….…………………….. 22 1.2.3- The polymer……………………………………………….. ………………………………….. 23 1.2.4- From cellulose to fibre ………………………………………………………………………… 24 1.2.5- Other components of plant fibres……………………………………………….. …………... 25 1.2.6- Differences between different types of fibres…………………………………………… ... 25 1.3 - The degradation of textiles / cellulose………………………………………………………….. 27 1.3.1- Chemical degradation…………………………………………………………………………. 27 1.3.2- Mechanical degradation ………………………………………………………………………. 31 1.3.3- Effect of the different degrading agents…………………………………………………… 31 2- The Reference Sample Collection……………………………………………... 39 2.1- The samples……………………………………………………………………………………….. 39 2.1.1 - Where from…………………………………………………………………………………….. 39 2.1.2- How many………………………………………………………………………………………. 40 2.1.3- What type……………………………………………………………………………………….. 41 2.1.4- What dates ……………………………………………………………………………………... 42 2.1.5- What painting materials……………………………………………….. ……………………... 44 2.2- The Access Database……………………………………………….. ………………………….. 44 Non-destructive condition assessment of painting canvases using NIR spectrometry, a PhD thesis submitted at the University of Barcelona by Marta OriolaFolch in December 2011 Contents 2.1- Fibre type………………………………………………………………………... 49 2.1.1 - Introduction……………………………………………………………………………………… 49 2.1.1.2 - Morphological characteristics of plant fibres…………………………………………… 51 2.1.2 - Materials and methods………………………………………………… ……………………... 54 2.1.3 - Results and discussion……………………………………………………………………….. 57 2.1.3.1- Fibre type of the paintings studied……………………………………………………….. 57 2.1.3.2 - Fibre type and date…………………………………………………………………………. 59 2.1.4 - Conclusions…………………………………………………………………………………….. 63 2.2- pH…………………………………………………………………………………. 65 2.2.1 - What is pH………………………………………………………………………………………. 65 2.2.1.1 - Why is acidity important to know ………………………………………………………….. 65 2.2.1.2 - How to measure pH ………………………………………………………………………… 66 2.2.1.3 - pH studies in paper research……………………………………………………………… 68 2.2.1.4 - pH studies on textiles / paintings ………………………………………………………….. 69 2.2.2 - Method development for measuring pH of paintings ………………………………………. 71 2.2.2.1 - Glass combination microelectrode versus ISFET probe……………………………… 72 2.2.2.2 - pH measurement of 10 test samples……………………………………………….. ….. 74 2.2.2.3 - pH measurement of 6 real samples……………………………………………….. …….. 76 2.2.2.4 - pH measurement of the Reference Sample Collection……………………………… ... 76 2.2.3 - Results and discussion……………………………………………….. ……………………... 77 2.2.3.1 - pH of the samples studied……………………………………………….. ……………….. 77 2.2.3.2 - pH and date………………………………………………………………………………….. 79 2.2.3.3 - pH and fibre type……………………………………………………………………………. 80 2.2.3.4 – A look at the deacidified samples in our Reference Sample Collection……………… 80 2.2.4 - Conclusions………………………………………………..………………………………….. 83 2.3 – DP……………………………………………………………………………….. 85 2.3.1- What is DP………………………………………………………………………………………. 85 2.3.1.1 - Relationship between DP and molecular weight ………………………………………. 86 2.3.1.2 – How to measure DP……………………………………………………………………….. 86 2.3.1.3 – DP standards and DP calculation……………………………………………………….. 87 2.3.1.4 - Relationship between DP and mechanical properties…………………………………. 88 2.3.1.5 - Relationship between DP and pH……………………………………………….. ………. 88 2.3.1.6 - DP & paper………………………………………………………………………………….. 89 2.3.1.7 - DP & textiles / paintings…………………………………………………………………… 89 2.3.2- Method development for DP determination of painting canvases……………………… 91 2.3.2.1- Needed amount of sample…………………………………………………………………. 91 Non-destructive condition assessment of painting canvases using NIR spectrometry, a PhD thesis submitted at the University of Barcelona by Marta OriolaFolch in December 2011 Contents 2.3.2.2- Cleaning the samples ………………………………………………………………………. 95 2.3.2.3- Sample defibering…………………………………………………………………………… 99 2.3.2.4- Viscometry……………………………………………………………………………………. 100 2.3.2.5- Evaluation of the method using Whatman paper……………………………………….. 103 2.3.2.6- Evaluation of the method using historical samples…………………………………….. 103 2.3.2.7- Evaluation of sample cleaning procedures……………………………………………….. 104 2.3.2.8- Evaluation of defibering by hand and using a mortar………………………………….. 105 2.3.2.9- Heterogeneity of a new canvas……………………………………………………………. 107 2.3.2.10- Heterogeneity of historical samples ……………………………………………………... 108 2.3.3- Results and discussion ………………………………………………………………………… 109 2.3.3.1- DP of the Reference Sample Collection……………………………………………….. ... 109 2.3.3.2- DP and date………………………………………………………………………………….. 110 2.3.3.3- DP and fibre type……………………………………………………………………………. 111 2.3.3.4- DP and pH……………………………………………………………………………………. 112 2.3.3.5- Comparison between protected and unprotected areas of the canvas……………… 113 2.3.3.6- Two samples from the same painting with visually different conditions……………… 114 2.3.3.7- Fibre type, pH, DP and date (PCA Analysis) …………………………………………….. 119 2.3.4 - Conclusions………………………………………………… ………………………………….. 121 3- NIR spectrometry/chemometrics for easel paintings……………………… 123 3.1- NIR spectrometry and chemometrics…………………………………………………………… 123 3.1.1 - Electromagnetic radiation…………………………………………………………………….. 123 3.1.2 - Infrared radiation………………………………………………………………………………. 124 3.1.3 - NIR spectroscopy……………………………………………………………………………... 125 3.1.4 - NIR spectra…………………………………………………………………………………….. 126 3.1.5 - Chemometrics…………………………………………………………………………………. 126 3.1.6 - NIR spectrometry and Chemometrics………………………………………………………. 127 3.2 - Materials and methods…………………………………………………………………………... 131 3.2.1 - Labspec 5000………………………………………………………………………………….. 131 3.2.2 - Grams AI spectroscopy software……………………………………………………………. 134 3.2.3 - Calibration (Grams IQ) ………………………………………………………………………. 135 3.2.4 - Validation (IQ Predict) ……………………………………………………………………….. 136 3.2.5 - Method development for pH…………………………………………………………………