Analytical Archaeometry: Selected Topics - Hardcover

Hardcover

ISBN 10: 1849731624 ISBN 13: 9781849731621

Verlag: Royal Society of Chemistry, 2012

Inhaltsangabe

Analytical Archaeometry describes this interesting and challenging field of research - on the border between natural sciences (chemistry, spectroscopy, biology, geology) and humanities (archaeology, (art-)history, conservation sciences). It fills the gap between these two areas whilst focussing on the analytical aspects of this research field. The first part of the book studies the main analytical techniques used in this research field. The second part expands from the different types of materials usually encountered, and the final part is organised around a series of typical research questions. The book is not only focussed on archaeological materials, but is also accessible to a broader lay audience. Overall the book is clearly structured and gives insight into different approaches to the study of analytical providing extensive discussion on a wide range of techniques, materials, questions and applications. Due to the advances in analytical instrumentation and applications in this field, it is important to have all this information merged together. Academics as well as professionals in archaeology, art history, museum labs and conservation science will find this an invaluable reference source ensuring the reader is provided with the latest progress in this research field.

Über diesen Titel

Über die Autorin bzw. den Autor

Professor Howell GM Edwards has published over 430 research papers in Raman spectroscopy and is on the Editorial Advisory Boards of the Journal of Raman Spectroscopy, Spectrochimica Acta: Biomolecular Spectroscopy, the Internet Journal of Vibrational Spectroscopy and the Asian Journal of Spectroscopy. He has supervised 40 research students for Ph.D degrees. Currently, he has research collaborations with groups in Spain, France, Denmark, Germany, Australia, Brazil and the USA. He has lectured widely on Raman spectroscopy and its applications including Plenary and Invited Lectures in Brazil, Australia, Finland, Denmark, Spain, France, South Africa, U.S.A and Germany. Sponsors of his research work include Bruker (Germany), Stiefel Pharmaceuticals, British Nuclear Fuels plc, ICI, BP, Purolite Intl. (USA), British Antarctic Survey, Repsol (Spain), the British Council and Elf Aquitaine (France). Professor Edwards is also national committee member of the Molecular Spectroscopy Group of the Royal Society of Chemistry and also of the UK Astrobiology Panel. Peter Vandenabeele is Professor of Archaeometry at the University of Ghent, Belgium. His main research interests are the application of Raman and analytical techniques to archaeology and art materials , dyestuffs , wall paintings and ceramics.

Von der hinteren Coverseite

Analytical Archaeometry describes this interesting and challenging field of research - on the border between natural sciences (chemistry, spectroscopy, biology, geology) and humanities (archaeology, (art-)history, conservation sciences). It fills the gap between these two areas whilst focussing on the analytical aspects of this research field. The first part of the book studies the main analytical techniques used in this research field. The second part expands from the different types of materials usually encountered, and the final part is organised around a series of typical research questions. The book is not only focussed on archaeological materials, but is also accessible to a broader lay audience. Overall the book is clearly structured and gives insight into different approaches to the study of analytical providing extensive discussion on a wide range of techniques, materials, questions and applications. Due to the advances in analytical instrumentation and applications in this field, it is important to have all this information merged together. Academics as well as professionals in archaeology, art history, museum labs and conservation science will find this an invaluable reference source ensuring the reader is provided with the latest progress in this research field.

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Analytical Archaeometry

Selected Topics

By Howell Edwards, Peter Vandenabeele

The Royal Society of Chemistry

Copyright © 2012 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-162-1

Contents

ANALYTICAL METHODS, 
Chapter 1 Methods of Visualisation G. Verhoeven, 
Chapter 2 Vibrational Spectroscopy: Theoretical Basis Relevant to Archaeometry and Archaeological Applications H. G. M. Edwards and P. Vandenabeele, 
Chapter 3 X-Ray Methods H. Calvo del Castillo and D. Strivay, 
Chapter 4 Radiocarbon Dating M. Van Strydonck, 
Chapter 5 Separation Techniques in Archaeometry S. Saverwyns and I. Vanden Berghe, 
Chapter 6 Mass Spectrometry I. Kuleff and R. Djingova, 
Chapter 7 Electrochemical Techniques A. Doménech-Carbó, 
MATERIALS, 
Chapter 8 Pottery, Glass and Enamelled Artefacts: How to Extract Information on their Manufacture Technology, Origin and Age? Ph. Colomban, 
Chapter 9 Glass L. Robinet and K. Eremin, 
Chapter 10 Gemstones and Minerals S. Karampelas and L. Kiefert, 
Chapter 11 Raman Spectroscopic Studies of Obsidian E. A. Carter, S. J. Kelloway, N. Kononenko and R. Torrence, 
Chapter 12 Pigments and Dyes P. Vandenabeele and H.G. M. Edwards, 
Chapter 13 Canvas and Panel Paintings: Techniques and Analyses E. Kouloumpi, A. P. Moutsatsou and A.-V. Terlixi, 
Chapter 14 Corrosion of Ferrous Archaeological and Cultural Heritage Artefacts Ph. Dillmann and D. Neff, 
Chapter 15 Resins and Fossil Resins J. Jehlicka, 
Chapter 16 Archaeological Ivories: A Challenge for Analytical Raman Spectroscopy H. G. M. Edwards and S. O'Connor, 
Chapter 17 Spectroscopy of Historic Textiles: a Unique 17th Century Bodice A. Hernanz, J. M. Gavira-Vallejo, M. C. Á lvarez, S. Martín, S. Montero, E. A. Carter, E. Gavrilenko and H. G. M. Edwards, 
Chapter 18 Identification and Authentication R. A. Goodall, 
Chapter 19 Technology of Production: The Master Potter 'Ali Muhammad Isfahani: Insights into the Production of Decorative Underglaze Painted Tiles in 19th Century Iran I. Reiche and F. Voigt, 
Chapter 20 The Application of Analytical Archaeometry in Underwater Cultural Heritage — A Case Study from Patagonia, Argentina D. Elkin, H.G.M. Edwards and M.S. Maier, 
Subject Index, 

CHAPTER 1

Methods of Visualisation

G. VERHOEVEN

1.1 Introduction

In the fields of cultural heritage, archaeology, art history and museology, many examination methods are based on imaging techniques. To date, numerous different imaging approaches exist, and although most of them have already existed for several decades, recent advantages in hard- and software technology make their application more straightforward than ever. In this chapter, an elementary but essential coverage of photodetectors, illumination equipment and signal composition will be provided to better understand the basic principles of common non-destructive scientific visualisations such as broadband colour photography, non-visible ultraviolet and infrared imaging, fluorescent photography, spectral imaging and X-ray radiography. Although important, many means to characterise and depict archaeological and heritage object will not be discussed (such as particle induced X-ray emission or PIXE, ultrasound techniques, thermography, stereomicroscopy, computed tomography, neutron imaging), nor will the file formats needed to store these visualisations and many other related archiving issues. For those interested in these topics, the following chapters of this book and the excellent compendium of MacDonald are recommended. Although several practical examples will illustrate each and every visualisation technique tackled in this chapter, it is still necessary to go back to some basic physics. Since imaging art objects and archaeological artefacts are all based upon some essential principles of how matter interacts with radiant energy, this chapter will start with a concise exploration of the world of matter, charge and energy.

1.1.1 Electromagnetic Radiation

Matter can be described as anything that occupies space and has weight. It is constituted by elements in various combinations. These elements, all described in the periodic table, are made up of atoms. Such atoms can be seen as the smallest matter particle, retaining all physical characteristics of an element. Different atom models were proposed during the last two centuries. Today, the Bohr model — introduced by Niels Bohr in 1913 — is often used, as it offers an easy way to depict the atom besides a relative correctness. In this model, the central core or nucleus of the atom is made up of chargeless neutrons and positively charged protons, whose amount is indicated by the atomic number Z. To compensate for these positive charges, negatively charged particles or electrons orbit this nucleus. Hence, it is correct to say that electric charge is substance-like and that all physical objects are composed of electric charge.

Charge differs from energy. Energy should not be looked at as a substance but rather as an attribute of a system that always turns out to be conserved. To be able to track energy flows, energy can be conceptualised by the model of fields. In the same way that a massive object can produce a gravity field to which distant objects respond, electrical charges and magnets alter the region of space around them so that they can exert forces on distant objects. It is exactly this altered space that is called a field (more technically, these fields are just vector quantities). Scientists have known since the early part of the 19th century that electrical fields and magnetic fields are intimately related to each other: moving electric charges (i.e. electric current) create a magnetic field and a changing magnetic field creates electrical current (thus electrical fields). A consequence of this is that changing electric and magnetic fields should trigger each other. The Scottish mathematician and physicist James Clerk Maxwell (1831–1879) put these ideas together and mathematically described the relationship between the magnetic and electric fields, as well as the currents and charges that create them. To conclude this line of reasoning, Maxwell said that visible light is an electromagnetic (EM) wave, consisting of both an electric (E) and magnetic (B) field (Figure 1.1). Both fields are oscillating perpendicular to each other as well as perpendicular to the direction of propagation (which makes them a transverse wave), whilst propagating at 299 792 458 m s-1 in vacuum. The latter speed is known as the speed of light, denoted c, and decreases when light travels in air, glass, water or other transparent substances.

The electric and magnetic component vectors vibrate in phase and are sinusoidal in nature: they oscillate in a periodic fashion as they propagate through space and have peaks and troughs (see Figure 1.1). Being a self-propagating and periodic wave-like phenomenon, EM radiation is distinguished by the length of its waves, called the wavelength (ITLλITL), its magnitude of change or amplitude (A) as well as its frequency (ITLλITL): a figure — expressed in Hertz (Hz) — that indicates the number of complete waves or sinusoidal cycles passing a certain point in one second and thus inversely proportional to ITLλITL. No matter what portion of this broad spectrum is considered, they all obey the same physical laws and the relation c = λv holds for each.

1.1.2 Light and Beyond-visible Radiation

The principle that allows the human visual system to observe objects and persons is based on those subjects' reflection of visible light. Dark objects do not reflect much incoming light, whereas a healthy banana principally reflects yellow light. However, this light is only one small portion out of the complete, so-called EM spectrum radiated by the sun or other sources (like stars or lamps). The EM spectrum can be considered a continuum of varying EM waves, all consisting of electric and magnetic fields that are described by the Maxwellian theory, but distinguishable by their wavelength.

Visible light ("light"), for instance, is only a very narrow spectral band with wavelengths ranging from approximately 400 nm (400 × 10-9 m) to 700 nm (700 × 10-9 m), the absolute thresholds varying from person to person and specific viewing conditions. These wavelengths correspond with frequencies comprised between 7.49 × 1014 Hz (749 THz) to 4.28 × 1014 Hz (428 THz). Nonetheless, the complete EM spectrum consists of far more particular wavebands with characteristic frequencies and related wavelengths that are not perceivable by the unaided normal human eye. To both sides of the visible band there is EM radiation which does not produce a visual sensation: gamma rays, X-rays, and ultraviolet (UV) rays with shorter-than-visible wavelengths (and higher frequencies), while infrared (IR) rays, microwaves, and radiowaves can be found in the long-wavelength, low-frequency region (Figure 1.2).

In addition to the aforementioned wave properties, EM radiant energy is known to exhibit particle-like behaviour and can be seen as a travelling bundle of photons (i.e. discrete energy packets) with energy levels that differ according to the wavelength. EM radiation can thus be considered a vehicle for transporting energy from the radiation source to a destination, photons being the particles of EM energy. To calculate a photon's quantum energy (E), Planck's constant h (i.e. 6.626 × 10-34 J s-1 or 4.136 × 10-15 eV s-1) must be multiplied by the frequency v of the radiation.

Due to this quantization, a visible photon with a wavelength of 650 nm will always have 1.9 eV of energy, while an ultraviolet 345 nm wavelength is characterised by photons with quantum energies of 3.6 eV. From these figures, it is obvious that shorter wavelengths have higher radiative energies (see also Figure 1.2). None of the wave-like and particle-like descriptions is complete by itself, but each of them a valid description of some aspects of EM radiation behaviour. This wave–particle duality is still one of the key concepts in quantum mechanics.

This chapter will be mainly restricted to imaging in the optical radiation spectrum. Although the limits (and also the number of subdivisions) are to a certain extent dependent on the discipline dealing with EM radiation and hence largely varying through literature, it is commonly accepted that the optical spectral band reaches from the UV to the IR. Since the subdivisions in one spectral band are not unified amongst various sciences, one finds several outer limits for the optical radiation spectrum. As was also defined by Palmer and Grant and Ohno, optical radiation is here defined as EM waves with wavelengths between 10 nm (0.01 µm) to 1 mm (1000 µm). In this way, it exactly covers a five-decade frequency range from 3 × 1011 Hz to 3 × 1016 Hz and can be logically subdivided into various spectral bands (Figure 1.3). The designation of spectral sub-ranges also varies, with the largest variability in the infrared band (even in the same discipline). Often, one finds NIR (see Figure 1.3 for abbreviations) to end at 1400 nm and SWIR finishing at 2500 nm. Additionally, the visible and NIR range are often referred to as the VNIR band. In the UV region, there is slightly more agreement, although UV-D is sometimes not considered to be part of the optical radiation spectrum.

Both the UV and IR region have the advantage that they can convey information about an object that remains unnoticed by the human eye. In this chapter, the optical radiation under consideration will be restricted to the NUV-SWIR wavelengths, as this is the most common spectral region used in (heritage) imaging. However, the final part of this chapter will delve a bit deeper in the X-ray region. While X-rays do not belong to the optical band of EM radiation, they have been used for over a century as a diagnostic tool in cultural heritage imaging. As such, X-ray radiography completes the triad of imaging phenomena outside the visible light that will be tackled here. Before delving deeper into these topics, it is useful to look more closely at the possible detectors for optical radiation and create a broader understanding of the terms signal and noise.

1.2 Detecting and Imaging Optical Radiation

1.2.1 Principles

Imaging a medium is always dependent on the influence of matter on incident EM radiation, which involves processes such as refraction, polarization change, specular reflection, scattering and absorbance. In a simplified form: the surface of any natural and synthetic object transmits, reflects, and absorbs EM radiation in varying ratios. Besides the specific chemical and physical structure of the object, this interaction and particular ratio of the three processes is wavelength dependent. The reflectance of an object can thus be described as the ratio of all the energy reflected (or scattered) by the surface versus the total amount of incident energy. When defined per unit wavelength, reflectance is termed spectral reflectance. A medium-specific spectral signature/spectral reflectance curve/spectral reflectance distribution is yielded when the spectral reflectance is plotted over a specific spectral range (see Figure 1.4). Recording this spectral signature not only tells us what colour an object has, but can also give insight into its chemical composition, since the heterogeneity of diverse elements in an object gives rise to different matter–radiation interactions and creates contrast in an image. However, detecting and imaging such a reflectance spectrum is not that straightforward, since imaging optical radiation involves in many cases a multiplicative effect: only the portion of the incoming radiation that is reflected by the object will be imaged (Figure 1.4).

This shows why human vision, colour photography or any kind of optical digital imaging (except fluorescence and thermal imaging in which only the emitted EM radiation is recorded) generates a signal that is the outcome of a three-variable process. First, there is the radiation source which has a certain spectral power distribution I(λ): i.e. a certain "amount" of radiation emitted at each wavelength. Secondly, the object itself has certain reflection properties which will vary per wavelength: R(λ). The combination of both incoming EM energy and reflection [I(λ) × R(λ)] creates a spectral distribution φ(λ) that is sampled by the human eye or the digital imaging sensor. Those also have their own spectral response; they will absorb the photons in specific spectral regions and interpret them. To make things even more complicated, also the viewing and illumination geometry matter, although these will be omitted in this chapter. When one of those three parameters changes, the visual sensation or the pixel values in the digital image will differ.

In the next session, a short overview will be presented on sensors commonly used for optical imaging.

1.2.2 Photodetectors

1.2.2.1 The Human Visual System

A very important and certainly the most familiar detector of optical radiation is the human eye and brain, together forming the human visual system. To enable vision under dim lighting conditions (scotopic vision), about 100 million very light-sensitive rods are used. Since rods only send information about the quantity of light, night vision is said to be colour-blind. When the light becomes more intense (from bright moonlight up), the rods gradually stop functioning as they get saturated. More importantly, colours will appear as the five to six million cones come into play: i.e. photopic vision. Most humans have three cone variants with a specific response to visible wavelengths (Figure 1.4): short-, middle-, and long-wavelength sensitive cones (S, M, and L), named according to the part of the visible spectrum to which they are most sensitive and characterised by peak sensitivities λmax at about 445 nm, 540 nm, and 565 nm respectively. Due to its working principle based on three different cone types, the human colour vision is said to be trichromatic. Figure 1.4 shows that the three receptors have a quite broad waveband to which they respond and there is significant overlap between the three responses.

(Continues...)

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Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2012
• Sprache: Englisch
• ISBN 10: 1849731624
• ISBN 13: 9781849731621
• Einband: Tapa dura
• Anzahl der Seiten: 593
• Herausgeber: Edwards Howell, Vandenabeele Peter
• Kontakt zum Hersteller: Nicht verfügbar