1. Analysis of Ancient Materials and their degradation – Lecture 3
CH-406
Prof. Dr. Claire Gervais

2. Content Introduction to Materials Introduction to ancient materials
Materials: definitions, multidisciplinarity, challenges
The triangle Structure-Property-Function
Materials research: Why, What, How, Where?
Introduction to ancient materials
Diversity of ancient materials: paintings, archaological objects, fossils, ivory, ceramics.
What is ancient? The concept of materials history and impact on their scientific study
Typical reasearch topics in ancient materials
Analyzing ancient materials: key concepts
Heterogeneity in materials: a fuzzy concept with clear consequences.
Too big or not too big? The art of adapting measurement scale to property scale.
Sample preparation: bulk, cross-sections, thin-sections, porous materials.
Example: Embedding techniques for thin sections of brittle paint samples.

3. Content Synchrotron techniques for ancient materials
Synchrotron light: generation and specificities
A specific synchrotron technique: X-ray absorption spectroscopy
Example: Degradation of smalt pigment in paintings
X-ray tomography techniques: Going to 3D and 4D imaging
Materials through the X-ray beam: attenuation coefficients
Acquiring a 3D image: Acquisition and reconstruction (principles)
Basics of image processing: filtering, segmentation, labelization
Example: Virtual unfolding of ancient manuscripts
Physico-chemistry of materials degradation
Reproducing and accelerating natural aging: limits of validity.
In-situ analysis of degradation processes.
Radiation damage: how to evaluate it and minimize it.
Example: Radiation damage of Prussian blue paper artworks

4. Take-home lesson 1 & 2
Materials often designed/defined by the interest we have in them: multifunctional, synthetic, biogenic, composite, ancient, natural, raw.....
Characterizing materials = characterizing a particular set of functions / properties / component structures, along with relationships between components (interface, distribution).
Heterogeneity conditions the scale at which obtaining a correct measurement and requires adequate statistical processing.
Correct characterization = Adapt the length scale of the measurement to that of the feature of interest.

5. Contents of the lecture
Imaging techniques
Examples: Catalyst and Eucalyptus Leaves
A note on sample preparation
A note on radiation damage

6. Materials characterization in a nutshell
Define the research question: WHY / WHAT / WHERE (the most important part of the study)
Choose the technique accordingly: HOW
Sample preparation: sometimes 90% of the work!
Measuring, imaging the sample
Data processing (representativity, filtering, REV, statistics)

7. Your task for the exam

8. Your task for assignments and exam
A. Locate the Why? What? Where? and How?
Give lines and pages or highlight in color the pdf
Answer to each with a short paragraph (if it is not clear in the publication, tell it!)
B. Choice of technique
Explain link between technique and question to answer
e.g.: Technique X chosen because sensitivity to structural feature / spatial / non-destructive / ...etc.
C. Statistics and representativity
How did they handle statistical significance?
Give lines and pages or highlight in color the pdf
D. Explain one experiment
From sample preparation to Data acquisition to Data processing

9. Your task for assignments and exam
A. Locate the Why? What? Where? and How?
Give lines and pages or highlight in color the pdf
Answer to each with a short paragraph (if it is not clear in the publication, tell it!)
Assignments (written) : 3-4 pages, in English, structured with these 4 blocks (A–D).
Appendix: annotated pdf, images (if you want)
Oral exam with the same structure
B. Choice of technique
Explain link between technique and question to answer
e.g.: Technique X chosen because sensitivity to structural feature / spatial / non-destructive / ...etc.
C. Statistics and representativity
How did they handle statistical significance?
Give lines and pages or highlight in color the pdf
D. Explain one experiment
From sample preparation to Data acquisition to Data processing

10. Imaging of Materials

11. What is imaging of materials?
Definition: Visual representation of a volume/surface of the material that highlights the spatial distribution of the property, chemical element or phase of interest.
Vocabulary:
Representation of surface: 2D imaging (dimensionality)
Representation of volume: 3D imaging or tomography (technique)
Interest in element or chemical property: chemical imaging (property)
Interest in morphology and micro-structure: micrograph (scale)

12. Imaging modalities
Legrand, S. et al., ”Examination of historical paintings by state-of-the-art hyperspectral imaging methods: from scanning infra-red spectroscopy to computed X-ray laminography”, Heritage Science, 2014, 2:13

13. Imaging modalities
– Full-field: an image is formed from interaction of the object with an extended beam
FTIR-FPA imaging, X-ray tomography
– Raster-scanning: the object is scanned in front of a focused beam
Raman imaging, Scanning X-ray fluorescence
Legrand, S. et al., ”Examination of historical paintings by state-of-the-art hyperspectral imaging methods: from scanning infra-red spectroscopy to computed X-ray laminography”, Heritage Science, 2014, 2:13

14. Raster scanning imaging

15. Example 1: Gold in leavesCu
Sr (oxalate crystals) Au
500μm
50μm
Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold
deposits”, Nature comm., 2013, 4, pp 2041.

16. Example 1: Gold in leavesCu
Sr (oxalate crystals) Au
50μm
Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold
deposits”, Nature comm., 2013, 4, pp 2041.

17. Example 1: Gold in leaves
Exercise (facultative): Find out HOW these images were done. From sample preparation to data acquisition and image processing. (Part D of Exam). Draw or Text.
50μm
Lintern et al. ”Natural gold particles in Eucalyptus leaves and their relevance to exploration for buried gold
deposits”, Nature comm., 2013, 4, pp 2041.

18. Example 2: Nanoscale imaging of catalysts at work
before treatment
after 2hours in H2
after 4hours in gas
50μm
De Smit et al., ”Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy”,
Nature Letters, 2008, 458, pp 222–225.

19. Example 2: Nanoscale imaging of catalysts at work
Exercise (facultative): Find out the WHY/WHAT/WHERE in the introduction of the paper (Part A of Exam). Highlight in the text.
50μm
De Smit et al., ”Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy”,
Nature Letters, 2008, 458, pp 222–225.

20. Sample preparation

21. Why preparing samples in imaging techniques?
To access bulk/surface properties or phases
To target specific features or phases
For imaging techniques
Air-glass interface (Optical Microscopy)
Carbon Nanotube on carbon fiber (Scanning Electron Microscopy)
Pharmaceutical
(Raman mapping)

22. Importance of sample preparation
– Very important step: ”bad” data cannot give beautiful results,
even with excellent post-processing.
– Sample preparation depends on technique specificities (scale,
surface, bulk, imaging, quantification) and material properties
(conducting, porous, brittle, layered).
– Examples:
Focusing techniques require flat surface to stay in focus.
Full-field techniques require a sample in the field of view
Tomography needs a sample thin enough to allow transmission
Brittle samples need to be embedded

23. Importance of sample preparation
With mechanical polishing
With ion milling

24. Importance of sample preparation
Sample not cleaned after polishing
Sample thoroughly cleaned

25. Typical sample preparation pathway for imaging
Cross-section preparation with
mounting-polishing (but there are
many, many other types of
preparation techniques!)
1 Mounting / Embedding
2 Grinding
3 Polishing
4 (Etching)

26. 1. Mounting / Embedding
Goal: allow samples to be handled easily and protects them from
mechanical damages (important for porous materials).
Practical: Should not influence the specimen (chemically or
mechanically) and should not interfere too much with the analysis.
Most often: epoxy, acrylic or polyester resin.

27. 2. Grinding
Goal: Get a flat surface and remove scratches that may interfere
with imaging.
Practical 1: Done usually with silicon carbide papers of different
grain sizes. Paper grit size: number of grains of silicon carbide per
square inch (180 grit paper is coarser than 1200 – finest).

28. 3. Polishing Goal: Get a flat and smooth surface suitable for imaging.
Practical: Soft cloth impregnated with abrasive diamond particles
(6μm and 1μm) and an oily lubricant. Usually need to wash but
debris can remain at the surface. Electrochemical or chemical
polishing can help in removing these debris.

29. 4. Etching
Goal: Enhance contrasts, for instance between metallic grains.

30. Example of optimal preparation
Meirer, JAAS, 2013

31. Warning... High photon flux and micro/nanoscale can lead to radiation
damage. Needs to be taken into account in the analytical pathway

32. Warning... High photon flux and micro/nanoscale can lead to radiation
damage. Needs to be taken into account in the analytical pathway

33. Take-home lesson
1. Imaging techniques allow to keep track of heterogeneity in materials and get statistically relevant information
2. Imaging requires to take into account constraints due to both material and technique
3. Sample preparations may not be trivial but is very important (bad samples = bad data)