• No results found

7. DISCUSSION

7.5. Identification Tool Interpretation

7.5.1. Interpreting the Identification Tool

# General Stratigraphy Macro Image Color Texture/

Distribution

Identification:

FTIR/

SEM-EDX

Corrosion Product 1 (CP1)

White Highly crystalline/

Circular

Mixture including:

Whewellite, a calcium oxalate.

Corrosion Product 2 (CP2)

White

Powdery/

Isolated, generally eliptical

Copper sulphate/

Copper + Sulfur

Corrosion Product 3 (CP3)

White

Highly crystalline/

Thicker in crevasses, otherwise even

Copper + Sulfur Zinc + Oxygen

Corrosion Product 4 (CP4)

White

Highly crystalline/

Blotchy blooms, unevenly distributed on

surface

Zinc+ Oxygen

Corrosion Product 5 (CP 5)

Light blue

Hard, thin crust, light powder beneath /

Even, crystalline

surface

Mixture including copper

carbonate / Copper+Chlorine

Iron+Oxygen

Corrosion Product 6 (CP 6)

Light blue

Powdery/

Evenly

distributed Copper+Chlorine

Corrosion Product 7 (CP 7)

Light blue

Waxy layer, powder beneath /

Smooth surface with

some light powder above

Paratacamite

Corrosion Product 8 (CP 8)

Green/

blue

Shiny, bubbly layer, powder beneath / Precipitating

from the bottom of a corrosion pit

Calcium + Carbon

Corrosion Product 9 (CP9)

Green/

blue

Gloss above light blue

powder/

Evenly distributed

Copper + Chlorine Copper + Sulfur

Phosphorus

Table 7.5.1. Identification Tool Interpretation Indicating Generalized Stratigraphy, Macro Images, Texture, And FTIR/SEM-EDX Results. FTIR conducted by Suzan de Groot, SEM-EDX conducted at 20 kV by Inneke Joosten (RCE). SEM-EDX results are based on the author’s interpretation of significant spectra peaks, so some elements are excluded. Full results of analysis can be found in Appendix II.

Corrosion Product 10 (CP10)

Bright blue

Thick, darker crust above light powder/

Unevenly distributed

Copper+Chlorine Copper+Sulfur

Calcium

Corrosion Product 11 (CP 11)

Electric blue

Hard, thin crust, light powder beneath /

Unevenly distributed

Tin/copper +Oxygen

CHAPTER 8 CONCLUSION

Wreck finds are an integral component of the archaeological record. At the same time, objects recovered from shipwrecks can face complete destruction due to their degradation processes. Cupreous wreck finds are subject to this issue due to the devastating impact of bronze disease. This makes treatment of the utmost importance, but even seemingly mild treatments can cause irreversible damage to artifacts. A lack of documentation of wreck findsaround the turn of the 20th century impedes current understanding of the real-time, long-term impact of early nautical archaeological conservation treatments. This is true of the Hollandia collection, which suffers from a lack of associated treatment documentation. The archival material pertaining to the Hollandia is extensive when it comes to archaeological records, but conservation treatment records are far from complete and does not provide conservators with enough context to understand how to care for these objects.

The extensive and unexplained corrosion discussed in this study is not limited to the Hollandia collection. Many wreck finds were treated using aggressive methods and have since been dissociated from their treatment records. Rarely are these custodians armed with extensive experience and analytic tools available to Rijksmuseum curators, and yet these excrescences are still enigmatic to them. The results of this research serves to bridge the gaps between the corrosion phenomena observed on treated wreck finds, and an understanding of the mechanism that drives these processes. The translation of these results into visual concept maps with associated archaeometric interpretations may help to transfer the knowledge of conservation scientists to custodians of unstable treated wreck finds. A visual tool in the format of a flow chart of corrosion products and their likely sources was created for the collection.

The analysis utilized in this project was designed to answer the research question of what can be said about the condition of cupreous objects from the Rijksmuseum’s Hollandia collection based on an analysis of their corrosion products. This question was effectively answered through the subquestions of:

Do alloying elements influence the development of active corrosion in the Hollandia collection?

• Do composite materials influence the development of active corrosion in the Hollandia collection?

• Is it possible to distinguish chemical and visual markers of the burial environment of objects?

• Is it possible to distinguish chemical and visual markers of the previous treatment of objects?

The alloy, burial environment, and previous treatments all play a role in the corrosion and excrescences observed in this thesis. Though most of the analysis in this thesis is qualitative rather than quantitative, XRF and SEM-EDX indicated the general elemental composition of

the alloys and contaminants present on the surface of objects throughout the collection, while FTIR indicated specific compounds present in excrescences. Two of the selected corrosion products were determined to be potentially active: paratacamite, for its status as a corrosive copper hydroxychloride, and calcium carbonate, not for its composition but for the dealloying observed on the metal on which it sits.

The next steps for the cupreous wreck finds in the Hollandia collection include being assessed by Rijksmuseum conservators prior to treatment. The concept map produced by this research provides an understanding of some corrosion phenomena present in the collection.

Through this study, a correlation was found between the appearance of the corrosion products present in the Hollandia collection and their elemental composition, along with the identification of two harmful corrosion processes. These are expressed in an identification tool, which can help conservators in the Rijksmuseum to interpret the corrosion they see on the surface of objects.

Future research on these or similar objects could be conducted in order to better understand the corrosion, excrescences, and state of wreck finds treated in the past. Elemental analysis is not able to determine the exact corrosion products on each object. A proposed design for a study of this kind in the future would begin with X-ray fluorescence that could performed in situ to determine the surficial elemental composition of an object and its corrosion, which can be identified if sampled and analyzed through the combined use of FTIR and Raman spectroscopy. A visual identification protocol that synthesizes the results of these analyses on wreck finds would make for a powerful tool.

Visual identification tools have the potential to aid conservators, curators, archaeologists, and others in understanding the condition of a collection. An expansion of this study, or studies of this type which produce visual identification tools could be helpful to other custodians who are confronted with complex corrosion phenomena on cupreous wreck finds.

There is little time or money allocated to the conservation of wreck finds, much less opportunities to carry out analysis. The translation of the rigorous research done at institutions such as the Rijksmuseum into visual tools available to archaeologists could have a great impact on the way wreck finds are cared for in collections around the world.

Works Cited

Babits, Lawrence, and Hans Van Tilburg. Maritime Archaeology: A Reader of Substantive and Theoretical Contributions. 1st ed. The Plenum Series in Underwater Archaeology, I.

College Station, United States of America: Institute of Nautical Archaeology, 1998.

Bass, George. Promise of Underwater Archaeology in Retrospect. College Station, United States of America: The Institute of Nautical Archaeology, 1983.

Brugge, Jeroen ter. “Wreck Finds in the Rijksmuseum: Valuation and Direction for the Future.” Discussed/established in departmental history meeting on 1 October 2018.

Amsterdam, The Netherlands: Rijksmuseum, September 2018.

Caldararo, Leo. “Some Effects of the Use of Ultrasonic Devices in Conservation and the Question of Standards for Cleaning Objects.” North American Archaeologist 14, no. 4 (n.d.): 289–303.

Edwards, Howell, and Peter Vandenabeele, eds. “Preface.” In Analytical Archaeometry. The Royal Society of Chemistry, 2012.

Evans, U. “The Corrosion Situation: Past, Present and Future.” Chemistry and Industry 70 (1951): 706–11.

Gawronski, Jerzy. “Hollandia.” In Encyclopaedia of Underwater and Maritime Archaeology, 196–97 and 329. London, United Kingdom: Yale University Press, 1998.

Gawronski, Jerzy. “Ships and Cities in Maritime Archaeology. The VOC-Ship Amsterdam and a Biographical Archaeology of Eighteenth-Century Amsterdam,” 79–108.

Amsterdam: Stichting Nederlands Museum voor Anthropologie en Praehistorie, 2014.

Hamilton, Donny. Methods for Conserving Archaeological Material from Underwater Sites.

College Station, United States of America: Center for Maritime Archaeology and Conservation Texas A&M University, 1998.

Harpster, Matthew. “Shipwreck Identity, Methodology, and Nautical Archaeology.” Journal of Archaeological Method and Theory 20, no. 4 (2013): 588–622.

Heginbotham, A. “CHARMed PyMca, Part I: A Protocol for Improved Inter-Laboratory Reproducibility in the Quantitative ED-XRF Analysis of Copper Alloys.”

Archaeometry, 2017.

Jedrejewska, Hanna. “A Corroded Egyptian Bronze: Cleaning and Discoveries.” Studies in Conservation 21, no. 3 (1976): 101–14. https://doi.org/10.1179/sic.1976.020.

Karen Leyssens. “Monitoring the Conservation Treatment of Corroded Cupreous Artefacts:

The Use of Electrochemistry and Synchrotron Radiation Based Spectroelectrochemistry.” Dissertation, University of Ghent, 2016.

Macleod, Ian. “Conservation of Corroded Copper Alloys: A Comparison of New and

Traditional Methods of Removing Chloride Ions.” Studies in Conservation 32, no. 25 (1987): 25–40.

May, Eric, and Mark Jones, eds. Conservation Science Heritage Materials. Dorset, United Kingdom: The Royal Society of Chemistry, 2006.

Muños Viñas, Salvador. Contemporary Theory of Conservation. Oxford, England: Elsevier, 2005.

Oxley, Ian. “The Investigation of the Factors That Affect the Preservation of Underwater Archaeological Sites.” In Maritime Archaeology: A Reader of Substantive and Theoretical Contributions, edited by Lawrence Babits and Hans Van Tilburg, 1st ed., 523–30. The Plenum Series in Underwater Archaeology, I. College Station, United States of America: Institute of Nautical Archaeology, 1998.

Plenderleith, Harold. The Conservation of Antiquities and Works of Art. Oxford, England:

Oxford University Press, 1956.

Pye, Elizabeth. “Archaeological Conservation: Scientific Practice or Social Process?” In Conservation: Principles, Dilemmas and Uncomfortable Truths, 1st ed., 10–20.

London, England: Routledge, 2009.

Rathgen, Friederich. The Preservation of Antiquities: A Handbook for Curators. 1st ed.

Cambridge, United Kingdom: Cambridge University Press, 1905.

Scott, David. Copper and Bronze in Art: Corrosion, Colorants, Conservation. Los Angeles, United States of America: Getty Publications, 2002.

Sease, Catherine. “Benzotriazole: A Review for Conservators.” Studies in Conservation 23, no. 2 (1978): 76–85. https://doi.org/10.1179/sic.1978.011.

Selwyn, Lyndsie. Metals and Corrosion: A Handbook for the Conservation Professional.

2004. Ottawa, Canada: Canadian Conservation Institute, 2004.

Selwyn, Lyndsie, D. Rennie-Bisaillion, and N. Binnie. “Metal Corrosion Rates in Aqueous Treatments for Waterlogged Wood-Metal Composites.” Studies in Conservation 38, no. 3 (1993): 180–97.

Spier, R. “Ultrasonic Cleaning of Artefacts: A Preliminary Consideration.” American Antiquities 16, no. 3 (1961): 410–14.

The Department of Dutch History of the Rijksmuseum. Prijs Der Zee: Vondsten Uit Wrakken van OostIndievaarders. Amsterdam, The Netherlands: Rijksmuseum, 1980.

APPENDIX I

X-RAY FLOURESCENCE

The results indicated that all objects included copper, zinc, lead, nickel and tin. Surface contaminants including calcium, chlorine, and bromine were reported in the X-ray fluorescence analysis. Table I.1 generalizes the alloy based on XRF analysis, though the measurement is surficial, and especially unreliable in archaeological alloys.

Table I.1. Elemental composition

Fe Co Ni Cu Zn Ag SnK Pb

530 0.98 0.00 0.09 70.64 24.31 0.07 1.19 2.12

693 2.69 0.01 0.02 70.02 23.00 0.12 0.06 3.64

1458 0.37 0.00 0.08 77.04 16.72 0.14 0.04 5.79

1640 3.55 0.00 0.05 67.95 24.10 0.12 0.01 3.66

1717 0.28 -0.01 0.15 59.85 37.68 0.16 0.01 1.25

1717 60.70 0.09 0.10 14.46 2.47 4.04 0.96 10.41

1836 6.64 0.04 0.26 76.85 6.39 0.12 1.95 6.29

2007 72.10 0.08 0.01 7.58 4.27 0.14 2.16 5.71

2151 1.56 0.01 0.04 74.89 14.89 0.52 2.63 5.51

2804 8.67 0.05 0.02 72.06 15.17 0.21 0.06 2.25

2824 1.67 0.00 0.04 60.27 35.06 0.25 0.06 1.91

2982 63.68 0.10 0.02 15.14 6.38 0.29 0.11 7.27

3008 17.20 0.12 0.02 47.92 30.56 0.27 0.06 1.21

Table III.1. X-Ray Fluorescence Analysis Results Analysis carried out and calibrated by Arie Pappot (Rijksmuseum Amsterdam).

APPENDIX II

SCANNING ELECTRON MICROSCOPY/ENERGY DISPERSIVE X-RAY SPECTROSCOPY

NG 1980 27 H 530

Figure II.1. SEM Image of NG 1980 H 530 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL.Data collected by Dr. Inneke Joosten (RCE).

Figure II.2. SEM Image of NG 1980 H 530 and associated EDX Spectra 006. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL.Data collected by Dr. Inneke Joosten (RCE).

Figure II.3. SEM Image of NG 1980 H 530 and associated EDX Spectra 007. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H #693

Figure II.4. SEM Image of NG 1980 H 693 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 1458

Figure II.5. SEM Image of NG 1980 H 1458 and associated EDX Spectra 002. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 1717

Figure II.6. SEM Image of NG 1980 H 1717 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 1640

Figure II.7. SEM Image of NG 1980 H 1640 and associated EDX Spectra 006. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 1836

Figure II.8. SEM Image of NG 1980 H 1836 and associated EDX Spectra 003. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 2007

Figure II.9. SEM Image of NG 1980 H 2007 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 2151

Figure II.10. SEM Image of NG 1980 H 2151 and associated EDX Spectra 007. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 2804

Figure II.11. SEM Image of NG 1980 H 2804 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 2824

Figure II.12. SEM Image of NG 1980 H 2824 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 2982

Figure II.13. SEM Image of NG 1980 H 2982 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

NG 1980 27 H 3008

Figure II.14. SEM Image of NG 1980 H 3008 and associated EDX Spectra 001. Parameters: 20.0vK x10,000. JSM-IT700HR SEM JEOL with integrated EDX by JEOL. Data collected by Dr. Inneke Joosten (RCE).

APPENDIX III FTIR RESULTS

NG 1980 27 H 530

Figure III.1.1. PCA Image of NG 1980 H 530 and associated FTIR Spectra. Data collected by Suzan de Groot (RCE).

NG 1980 27 H 693

Figure III.2.1. NG 1980 H 693 FTIR Spectra. Data collected by Suzan de Groot (RCE).

NG 1980 27 H 1640

Figure III.3.1 NG 1980 H 1640 FTIR Spectra. Data collected by Suzan de Groot (RCE).

NG 1980 27 H 2982-A

Figure III.4.1 NG 1980 H 1640 FTIR Spectra. Data collected by Suzan de Groot (RCE).