Salt Damage Around a Bat Roost at Urnes Stave Church
Total Page:16
File Type:pdf, Size:1020Kb
Salt damage around a bat roost at Urnes stave church Kjersti Marie Ellewsen Masters Dissertation December 2019 The front page image shows a salt crystal within the wooden matrix sampled from inside the bat roost at Urnes stave church (sample 7). The image is taken with an SEM at the Imaging Centre at NMBU by Hilde Raanaas Kolstad. Mag. 1500 x ii Salt damage around a bat roost at Urnes stave church Kjersti Marie Ellewsen Supervisors: Noëlle Lynn Wenger Streeton, Department of Archaeology, Conservation and History iii © Kjersti Marie Ellewsen 2019 Salt Damage around a bat roost at Urnes stave church Kjersti Marie Elllewsen http://www.duo.uio.no Printing: Reprosentralen, University of Oslo iv Abstract Urnes stave church is dated to the 1130s and was inscribed on the UNESCO World Heritage List in 1979. In the south west nave corner, the bearing post and adjoining bressummer (sill beam) of original pine wood suffer from salt deterioration. The area is situated near a bat roost, and this has led to the assumption that the salts derive from bat urine. Examinations and different analytical methods were used to verify the source of the salts and examine the condition of the wood. On site investigations included test strips and portable XRF and X- ray. Samples were taken for analyses in ICP-OES, FTIR, SEM-EDX and light microscopy using lignin staining to answer the research questions. A wildlife camera, ultrasound detectors and climate loggers were part of the investigations at site to investigate present bat activity and assess the preservation climate inside the church. Other possible sources are excluded, and the conclusion is that the salts derive from bat droppings. Salt molecules found in the samples were mainly potassium sulphates and potassium phosphates. These substrates come from the bat faeces. The wood cells at the surface of the wooden construction suffer from mechanical tear due to salt crystallization, but the speed of the degradation is low. The crystallization point is not crossed often in the climate at Urnes due to the high deliquescence relative humidity of the molecules identified. No bats use the roost at present (2016-2019). Measures to desalinate the area and prevent bats from re-using the roost are presented. v Sammendrag Tittel: Saltskader rundt et flaggermusrede i Urnes stavkirke Urnes stavkirke er datert til 1130-tallet og ble innskrevet på UNESCOs verdensarvliste i 1979. Den sørvestre midtromsstaven og den tilstøtende svilla lider av saltnedbrytning. Området er i nærheten av et flaggermusrede, og dette har ført til antakelsen at saltene stammer fra flaggermusurin. Undersøkelser og forskjellige analysemetoder ble brukt for å verifisere kilden til saltene og undersøke treets tilstand. Undersøkelser på stedet ble utført med test strips og bærbar XRF og røntgen. Det ble tatt prøver for analyser i ICP-OES, FTIR, SEM-EDX og lysmikroskopi ved bruk av ligninfarging for å svare på forskningsspørsmålene. Et viltkamera, ultralyddetektorer og klimaloggere var en del av undersøkelsene på stedet for å undersøke flaggermusaktivitet og vurdere bevaringsklimaet i kirken. Andre mulige kilder til saltene er vurdert. Saltmolekyler som ble funnet i prøvene var hovedsakelig kaliumsulfater og kaliumfosfater. Disse molekylene kommer fra flaggermusenes ekskrementer. Trecellene på overflaten av trekonstruksjonen lider av mekanisk nedbrytning på grunn av saltkrystallisering. Krystalliseringspunktet for disse saltene krysses ikke ofte i klimaet på Urnes, og nedbrytningshastigheten er forholdsvis lav. Det er ikke påvist noen kjemisk nedbrytning. Flaggermus har ikke brukt redet i løpet av dette prosjektet (2016-2019), men det foreslås å fjerne saltene og hindre at flaggermus bruker kirken som tilholdssted. Avbøtende tiltak for flaggermusene, i tråd med Norges forpliktelser i EUROBATS-avtalen, anbefales. vi Acknowledgements A lot of people have been of big importance to me during the three years I spent on this project. I would like to start by thanking my employer, Riksantikvaren (The Directorate for Cultural Heritage), for the possibility of increasing my knowledge on salts in wood. To my leader Harald Ibenholt for his understanding, and for making it possible for me to spend a lot of time working on this master project. Thank you to the people at HR for giving me resources and time off to complete this project. I have also had great support from the librarians; Eva Christina Eide and Gurli Halin for their service finding literature about all sorts of strange things. Thank you to Jan Helge Skjærven for teaching me EndNote, which helped me keep track of the references. Thank you to my former colleague in the Conservation Department Sjur Mehlum for saying yes every time I asked for funding for analyses. Anders Amlo – thank you for your patient help with illustrations. Your attention to detail makes all the difference. And Ronny Haugan, thank you for crucial data help during the days of finalization. Last but not least, thank you to Leif Anker, for your always open door, for sharing your limitless knowledge about Urnes, and always giving me constructive and positive feedback on my drafts. THANK YOU to the owner of Urnes stave church, Fortidsminneforeningen (The National Trust of Norway), and several of the people there: Eli Sofie Thorne gave me access to the research material the first time I applied. Merete Winness has given me support and cheers through the project. Thank you Marit Bøen for giving me access to the church any time convenient for me and serving me your lovely cakes. My research at Urnes inspired a children’s project at Fortidsminneforeningen, created by Astrid Galstad, and the bat «Fortimus» is now a popular attraction for children who visit their stave churches. This has inspired me back. I have had great help with all the analyses. Susan Braovac delivered a comprehensive report from the FTIR analyses. Thank you to Sara Mantellato and Francesco Caruso who conducted the ICP- analyses at ETH Zürich in their spare time. Hilde Raanaas Kolstad at NMBU imaging centre ran the SEM analyses with me and provided extra analyses over and over when I had new thoughts and ideas. Her colleague YeonKyeong Lee conducted the lignin analyses. Susanne Kaun at NIKU helped me understand the XRF peaks. Thank you all! vii Thank you to Barbro Wedvik and Christina Spaarshuh at NIKU for going the one step too far in the challenging weather conditions at Urnes during the X-ray analysis. Thank you also to Erlend Gjelsvik for steady help with the airlift during the X-ray shooting. Thank you to Terje Thun at the National laboratory for dating, NTNU, for providing reference material from the raft beam at Urnes and explained dendro-dating to me. I have learned what I needed to know about bats from Tore Christian Michaelsen and Jeroen var der Kooij, and the PhD of James Hales about bats in churches has been a great help during this project. Thank you! Thank you to the people at the University of Oslo; To my supervisor Noëlle Lynn Wenger Streeton for teaching me how to write and giving me confidence, and Francesco Caruso for the well-run course on analytical instruments, and your last minute first aid about salt chemistry. It made all the difference to me! Thank you to Jostein Bergstøl for sharing your academic experience when I needed it, and to Marieanne Davy Ball for proof reading and always being a good friend. Thank you also to my two daughters, Milla and Sonja, and the rest of my family in Trøndelag, for your support, love and patience with me on stressful days. You are amazing! It has been fun, but I could not have done this without all of you! Kjersti Marie Ellewsen Kolbotn, December 2019 viii Table of Contents Abstract ................................................................................................................................................... v Sammendrag ........................................................................................................................................... vi Acknowledgements ............................................................................................................................... vii List of Figures ....................................................................................................................................... xii List of tables ......................................................................................................................................... xvi INTRODUCTION .................................................................................................................................. 3 Background ........................................................................................................................................ 3 The topic of this thesis........................................................................................................................ 4 Research questions ............................................................................................................................. 5 Dissertation structure .......................................................................................................................... 7 Theoretical background .......................................................................................................................... 9 Research object: Urnes stave church .................................................................................................. 9 The construction of the church ......................................................................................................