5/6/98
Christopher H. Kreb <Chkreb@aol.com>
Anthropology 521
Ultraviolet Fluorescence Analysis and Lithic Sourcing: An Overview
I. Background and Theory
Archaeology studies the material remains of the past, yet archaeologists
use only limited tools based in material science. While some techniques, like
radiocarbon dating, have become ubiquitous in archaeology, others remain underused
or unused. There are many reasons for this. Many techniques are destructive, ruling
out their use on rare or sacred artifacts. Some techniques are difficult to
understand, causing archaeologists to shy away for fear of a steep learning curve.
Above all, many techniques based in material science are expensive, placing them out
of reach for most run-of-the-mill archaeological applications. This last problem is
exacerbated by the fact that there is only limited discourse between the disciplines
of archaeology and the hard sciences. In a nutshell, we don’t know what they’re capable
of doing and they don’t know what we need (Leute 1987: vii, 1-2).
Optical examination is unquestionably the central method of analysis in
archaeology. Optical examination can be broken down into two broad categories: visual
examination and examination of radiation. In the first group are the most basic
techniques, including simply examining the artifact visually without magnification.
These techniques (including microscopy) provide mostly qualitative data. The latter
techniques, which involve examining objects using other types of light, such as
infrared, ultraviolet, and x-ray, provide both qualitative and quantitative data.
These non-visible forms of radiation can literally redefine how we see the object.
Features and patterns not obvious under visible light become clear and measurable
when bombarded by other forms of radiation. In general, all techniques concerned with
optical examination focus on the interaction (absorption and emission) of
electromagnetic radiation (Tite 1972: 195-7).
The focus of this examination is ultraviolet fluorescence. When lithic
artifacts contain compounds that fluoresce under ultraviolet light, they give off
a unique spectrum of radiation. This is the basis of ultraviolet fluorescence analysis
(UVFA). The emitted spectrum can be compared to library samples of spectra from
regional lithic sources to determine the origin of the stone in question. A major
focus of this examination is dedicated to the physics of light. Without this, it is
impossible to understand potential problems which may arise in experimental work and
to properly interpret the meaning of results. A brief section regarding
methodological and practical considerations follows, leading into the third section
on other methods used in lithic sourcing. The fourth section details my conclusions,
drawn directly from the preceding analysis and, finally, a brief fifth section
outlines the methodology I will use to examine lithics under ultraviolet light in
the lab.
To understand the fluorescence mechanism, some basic information about
the nature of light is necessary. Light has a dual nature: it is both particles and
waves. It can be thought of as an electromagnetic disturbance (wave) traveling in
a straight line (photon) at 3 x 108 m/s (C) in a vacuum. At right angles to the direction
of travel on both the vertical and horizontal planes are alternating electric and
magnetic fields. The frequency of oscillation of these fields determine the frequency
(n) of the light. The distance traveled in one full oscillation is the wavelength
(l) of the light. The speed, frequency and wavelength are related by the equation
C = nl. The energy of a photon is proportional to the frequency of the wave. When
a charged particle (e.g. an electron) is placed in the path of light, the particle
can absorb the energy under certain conditions. When the incoming light has a
wavelength between 100-380 nm (the ultraviolet band, see fig. I) it can cause the
charged particle to emit a photon of visible light. This is known as fluorescence.
One major problem with ultraviolet light is that it is impossible to get a line-free
continuous UV spectrum. Atomic spectra can be divided into continuous and line
spectra. Continuous spectra appear as continuous bands of light, blending into one
another (typical of radiation emitted by hot, luminous solids). Emission line spectra
consist of a few, discrete lines of color (typical of luminous gas) (Ostdiek et. al.
1995: 384-5; Leute 1987: 115-6; Schulman 1977: 15-7; Tite 1972: 197).
Ultraviolet radiation[1] (UV) is a band of electromagnetic (EM) waves
that begin just above the frequency of violet light (n = 1015 Hz) and extend to the
x-ray band(n = 1018 Hz). UV radiation is seen in nature in two basic ways. First,
UV light is part of the heat radiation emitted by very hot objects. For example, about
7% of the sun’s total radiation output appears in the UV band. Second, according to
Niels Bohr’s quantum model of the atom, UV radiation is also given off by an electron
in a changing state of excitation. This happens when an electron moves from a more
excited state to a less excited state. In quantum physics, the energy of electrons
in orbit around the nucleus of an atom are assigned a quantum number, beginning with
one (n = 1) and moving up. Each atom has a number of potential orbits in which electrons
can be found. When an electron changes states an energy-level transition occurs, in
which energy is released in some form. Electrons do not ordinarily stay in an excited
state for more than a billionth of a second (Ostdiek et. al. 1995: 303, 395-6; Leute
1987: 115; Schulman 1977: 25). The lifetime of an electron in the excited state is
actually quite long compared to other events on the molecular scale. For example,
the lifetime of an electron in the excited state (10-8 s) is 1000 times as long as
the time period for a single molecular rotation (10-14 s) (Rendell 1987: 3-4; Lakowicz
1991: 3). When an electron moves from a more excited state to a less excited state,
a photon of light can be emitted. The energy of the emitted photon can be calculated
by multiplying Planck’s constant (h = 6.63 x 10-34 J-s) by the frequency (n) of the
emitted photon (E = hn). The photon which is emitted has energy equal to the difference
between the energy for the two levels, and can be expressed as _E = E2 - E1. If the
type of photon emitted and the kind of atom from which it was emitted are known,
generalizations about what kind of energy-level transition took place can be made.
For example, if an electron from a hydrogen atom emits a UV photon, it can only mean
that the transition was one from any higher energy state (n = 2, n = 3 or n = 4) to
the ground state (n = 1) (Ostdiek et. al. 1995: G-3, 304, 380-2, 387, 397-8; Leute
1987: 115; Schulman 1977: 16).
The general process by which light is produced through some reaction is
called luminescence. Luminescence is most commonly associated with thermal processes
(thermoluminescence) or electrical processes (electroluminescence). Light not
associated with heat or electricity is much less common and is called cold light.
There are four processes by which cold light is produced: radioluminescence,
photoluminescence, bioluminescence, and chemiluminescence. All require the input of
some kind of energy in order to output light. The type of input is indicated by the
prefix. When certain substances are irradiated with UV light, it results in the
emission of photons of visible light. This reaction is named after the released
photons: photoluminescence (Ostdiek et. al. 1995: 304; Rendell 1987: 1-2).
The most widely used type of photoluminescence in analytical work is
fluorescence. The phenomenon of ultraviolet fluorescence has been known since at
least 1565, when the first reference appears in literature. It was named after the
mineral fluorspar, on which its effects were first seen (Rendell 1987: 3). By the
mid-1800’s, methodical study of fluorescence began. Since then, many disciplines have
used the unique properties of fluorescence to examine natural phenomena. However,
its use in archaeology has been limited (Jarvis 1995: 1).
The most important concept in understanding fluorescence is the
absorption process. When a molecule absorbs a photon of UV light, it undergoes a
transition to an excited electronic state, causing it to promote one (or more) of
its own electrons to a higher orbit. In 99% of cases at room temperature, the molecule
receiving the UV photon is in the ground state. After absorption, the molecule will
be in the excited state and may also begin vibration, depending on the energy of the
photon. This is known as excited vibration. Vibration is a confusing term because
it refers both to the total orbital angular momentum of the molecule (molecular
vibration) and to the spin angular momentum of individual electrons (referred to as
singlet and triplet states, discussed later). In this case, vibration means the total
orbital angular momentum of the molecule, which can be quantified in a Jablonski
diagram (see fig. II). Since wavelength and frequency are inversely proportional,
the shortest lines on a Jablonski diagram represent the longest wavelengths (low
energy means low frequency means long wavelength). The excess vibrational energy is
quickly dissipated through intermolecular thermal motion. This process is known as
vibrational relaxation and takes less than 10-10 s from the time the photon was
absorbed (Rendell 1987: 3-7, 10; Schulman 1977: 6-7, 9-10, 31; Becker 1969: 76-7,
88).
Absorption is a central concept because the absorption band is
fundamentally different from the emission band. Stokes’ Law states that the
fluorescence (emission) band will have a longer wavelength than the absorption band
because after the molecule absorbs a photon, it loses some energy through vibration
(radiationless transfer and inter-system crossing). Thus, some energy gained in
absorption is no longer available for radiation. It was this discovery, in 1852, that
laid the theoretical foundation for “whiter-than-white” commercial detergents, which
add a fluorescent compound to the soap. Traces of the compound remain on the fabric,
causing it to absorb UV radiation and emit at the blue end of the visual spectrum,
giving the illusion of more light reflecting from the fabric than is falling on it.
More sophisticated instruments used in fluorescence spectroscopy can record both the
incoming UV photon and the outgoing fluorescence. This absorption/emission spectrum
is known in fluorescence spectroscopy as the excitation spectrum. The difference
between the maximum excitation wavelength and the maximum emission wavelength is
known as the Stokes’ Shift, and is an important property of fluorescence (Rendell
1987: 10-12; Schulman 1977: 34; Becker 1969: 88-9). The Stokes’ Shift refers to the
loss of energy mentioned above, the mechanics of which are beyond the scope of this
paper.
Not every substance that absorbs UV radiation fluoresces. The preferred
method of quantifying fluorescence is called the quantum yield[2]. The quantum yield
is defined as the number of photons emitted divided by the number absorbed, which
can be related to the intensity of fluorescence divided by the intensity of
absorption. A high quantum yield number is associated with molecules with delocalized
systems of conjugated double bonds, which results in great rigidity. This explains
the extreme fluorescence of substances that contain fluorescein, anthracene, and
perylene. These substances also have very high absorption rates, following Stokes’
Law. From this we can generally say that rigid molecules fluoresce most readily.
However, since there are other methods of energy dissipation available, a rigid
molecular structure does not automatically mean it will fluoresce. It is difficult
to predict which materials will fluoresce because there is a delicate balance between
conflicting factors, including, but not limited to, those mentioned below (Rendell
1987: 24, 26).
If a substance absorbs UV radiation but does not fluoresce, it must
dispose of the energy in some other way. Sometimes, the UV radiation matches or exceeds
the energy required to break chemical bonds and is thus dissipated. A second method
of UV radiation dissipation is radiationless transfer of energy. This happens in two
ways. The first involves redistribution of energy intramolecularly, which consists
of internal conversion of energy followed by vibrational relaxation. Internal
conversion involves radiationless transfer between electronic states of the same
multiplicity (singlet ÷ singlet, discussed below). The second method combines
inter-and-intra-molecular redistribution of energy. It consists of three stages:
inter-system crossing, vibrational relaxation, and external quenching. Inter-system
crossing involves radiationless transfer between electronic states of different
multiplicity (singlet ÷ triplet, see fig. III) (Rendell 1987: 21-23, 42; Schulman
1977: 26-31; Becker 1969: 98, 101-4). “The proportion of energy lost in this way is
not known” (Becker 1969: 88).
If deactivation by collision is prevented, which can be achieved by
temperature reduction to 77_K, inter-system crossing will not result in radiationless
transfer. Instead, as the molecule returns to the ground state, radiation is emitted
in the form of phosphorescence. In this way, inter-system crossing can be controlled
for. The aforementioned characteristic is one fundamental difference between
fluorescence and phosphorescence. A second difference is that phosphorescence is of
a much longer duration, which can be controlled for by using solvents containing heavy
atoms, which decrease the lifetime and intensity of the phosphorescence (Rendell
1987: 30-2; Becker 1969: 94, 127, 221; Schulman 1977: 40-1). A related phenomenon
is called delayed fluorescence. It is also long-lived and results after a collision
imparts sufficient energy to a molecule in the excited state, which raises it to a
higher vibrational level. It can then return to the ground state by the emission of
a photon of the same wavelength as normal, thus prompting delayed fluorescence. The
intensity of delayed fluorescence is very small compared with normal fluorescence
(Rendell 1987: 32-3; Schulman 1977: 42-3; Becker 1969: 125-7).
Singlet and triplet states explain why phosphorescence has such a long
lifetime. The singlet state refers to an electronic state in which any spinning
electrons[3] in the same orbit have opposite spins, following the Pauli Exclusion
Principle. When a molecule becomes excited and promotes an electron to a higher energy
level, it can remain in the singlet state as long as the total electron spin remains
at zero (Rendell 1987: 37-8; Schulman 1977: 10).
When two electrons no longer share the same orbit, they are also no longer
bound by the Pauli Exclusion Principle. Hence, their spins can become parallel, which
creates three sub-states of energy, which are commonly referred to collectively as
the triplet state. Just as in the singlet state, molecules in the triplet state can
be at any level of excitation (Rendell 1987: 39; Schulman 1977: 11).
Molecules can arrive at the triplet state only through inter-system
crossing or, more infrequently, through some other non-radiative process such as a
chemical reaction. This is one of the rules of quantum mechanics, called the selection
rule, which states that “the electron spin cannot change during a transition
associated with the absorption or emission of radiation” (Rendell 1987: 41). Thus,
a molecule at the lowest level of triplet excitation cannot return to a singlet ground
state by emitting a photon. This explains why both phosphorescence and the triplet
state have long lifetimes (Rendell 1987: 41-2; Schulman 1977: 18).
Having discussed the underlying physics in some depth, we can now move
on to applications in archaeology. Different general categories of rocks can often
be identified by visual examination. However, it is much more difficult to identify
the exact source of any given artifact. “Geological outcrops in a single region can
be numerous and varied (points, veins, colluvial deposits, alluvial cones, volcanic
flows, fluvial terraces, moraines and marine deposits, etc.)” (Tixier et. al. 1992:
19; Tite 1972: 208).
One of the questions archaeologists ask seeks to relate the lithic
artifacts found at sites to distant quarry sites. Understanding this association can
help explain resource management, economics and territorial relationships. UVFA has
the potential to aid both field and laboratory archaeologists in this aim. The
principle of UVFA is simple: when certain artifacts are illuminated with UV light,
they fluoresce. The emitted spectrum (fluorescent light) is characteristic of the
chemical state of the surface. This can be helpful in aging the artifact, especially
in determining the sequence of flaking. In transparent objects, the UV light can
penetrate the surface and reveal the chemical state of the interior. Marbles and
precious stones have been successfully sourced using UV light in this way (Leute 1987:
116).
In order to fluoresce, a rock must contain what is commonly called an
activator. Fluorescent minerals consist of an activator and inert materials.
Activators may be present in varying quantities, occupying defects in the crystal
lattice or between grain boundaries. The quality and quantity of the activators
determine the spectrum of fluorescence. Some materials will not fluoresce even though
activators are present. This is due to a phenomenon known as quenching, which causes
molecules to disperse the energy of the incoming photon in some other way. Quenching
can cause decreased luminescence or even a total repression of luminescence.
Quenching can be divided into two broad categories: dynamic and static. Quenching
is a result of both inter-system crossing and radiationless transfer of energy, which
suppresses fluorescence. Typical static quenchers include mercury and bismuth, while
dynamic quenchers include iron, cobalt and nickel. For this reason, rocks with high
concentrations of these elements will not fluoresce under any conditions (Jarvis
1995: 4-5).
II. UVFA Methodology
Many types of UV lamps are commercially available, differing in vapor
pressure, number of lines, and intensity. Filters can be used to isolate lines and
thus offer an additional means of discrimination (Leute 1987: 116). Two types of
ultraviolet waves are typically generated by commercial equipment, called long and
shortwaves. Longwaves (3100-3800 angstroms (Å)) and shortwaves (2300-3100 Å) are
commonly both applied to specimens since fluorescence response is dependent on
wavelength. Shortwaves often provide the more dramatic response. Color and reaction
can be significantly different under different wavelengths and thus act as an internal
correction mechanism (Jarvis 1995: 4-6).
The work area around the specimen should have clean, non-reflective
surfaces. Black velvet is ideal. For the safety of the researcher and the integrity
of the experiment, there should be a plastic safety shield between the UV source and
the experimenter. Exposure to shortwave UV for extended periods can irritate and
ultimately damage the eye. Furthermore, the human eye fluoresces under UV and could
cause reflected light to interfere with the experiment (Jarvis 1995: 7). Although
no reference specifically refers to potential skin damage, it should be considered
and any researcher working under artificially produced UV light for extended periods
should take appropriate precautions.
Like any technique, it is clear that UVFA cannot be applied without
thought. The experimenter must try different methods with the goal of finding the
method most appropriate to the material being studied. Specifically, specimens should
be examined under as many different wavelengths as practical. Furthermore, if
applicable, the experimenter should attempt to expose samples to UV after the sample
has been cooled to under 77_K in liquid nitrogen, as this can provide an additional
spectrum for comparison. This should also be done using both long-and-short
wavelengths (Jarvis 1995: 5-6).
UVFA is a destructive technique, since it is important to examine a fresh
surface on a clean, dry specimen. In archaeological specimens, it would be wise to
examine both external patinated surfaces as well as internal surfaces. In addition
to this, it is important to note that the same lamp should be used throughout the
analysis of a single source. Wavelengths are highly variable, and even a slight change
in wavelength can potentially alter results. If possible, wave emission from the
source should be measured before each session. Researchers have reported that even
commercial lamps of identical brand and style produce slightly different wavelengths.
Furthermore, it is critical that the distances between lamp, object, camera, and
researcher remain consistent. Fluorescent intensity and color can be adversely
affected by proximity (Jarvis 1995: 6-7).
Another consideration, especially in archaeological applications where
overall effect is the goal, is the eyes of the researcher. Human eyes are not all
receptive to the same range of wavelengths. Colorblindness, age and various disorders
can cause a different perception of color. For this reason, it is best that a single
researcher view and record results. It is also important the the researcher allow
some amount of time to acclimate to the dark. If possible, fluorimeters, colormeters,
and spectrophotometers should be used to objectively record color. In the absence
of these expensive devices, a handheld photographic light meter is helpful (Jarvis
1995: 6-7).
Any serious study of UVFA requires photographic equipment capable of
producing color photographs of emitted UV radiation. The critical factor is that the
camera only photograph light emitted, not absorbed. For this reason, a filter which
transmits only visible light (4000 - 7000 Å) is indispensable. The film used should
also be considered. Films like Kodak Ektachrome 160 Tungsten are insensitive to
wavelengths below 4000 Å. Again, the key is the flexibility of the researcher. The
researcher must experiment with different films, filters, angles, and exposures to
find that which works best for the material being exposed. Furthermore, since no
standard currently exists for quantification of fluorescence intensity and color,
researchers have to determine which standard they will use. Most standards (like
Pantone) are designed for use under white light, which is difficult to use when trying
to view colors under UV light in a dark room (Jarvis 1995: 7-9).
III. Other Methods for Sourcing Lithics
In order to characterize lithics, something about the source must
distinguish it from products of other sources. Sources cannot (and should not) be
determined by visual examination alone. Considerable attention should be paid to the
raw material procurement strategy of the group that manufactured the material. It
should be determined whether the material in question is rare or abundant and whether
the material comes in more than one variety, among other important questions about
procurement. Furthermore, good geological mapping of the area is a prerequisite for
sourcing studies. Finally, assessment of the post-burial history of the artifact must
be determined. This is especially important for surface studies, since these can be
altered considerably by natural processes (Renfrew 1996: 342; Tixier et. al. 1992:
19).
There are many analytical methods available to archaeologists to source
lithics. The most simple is visual examination, which should be used with caution,
as mentioned above. The most common method of optical analysis is microscopic
examination by thin section. This involves viewing the section under a light
microscope, which allows identification of mineral structure. Rocks often have
minerals which are characteristic of a specific source. The main difficulties with
this method are time, expense and universality. Creating slides for microscopic study
is time consuming and expensive. Many types of rock (like flint) are insufficiently
distinctive for analysis (Renfrew 1996: 343: Tite 1972: 207).
By understanding the composition of artifacts, and comparing these
results with the composition of sources, archaeologists can determine the origin of
the raw material used to manufacture the artifact. To this end, various methods based
on the behavior of atoms have been developed. Optical emission spectrometry (OES)
is based on the principle of thermoluminescence. Since different elements have
different atomic line spectra, the object will give off radiation of those elements
present when heated by a carbon arc (Tite 1972: 309). The main problem with this method
is its low accuracy of ± 25%. It has been largely superseded by inductively coupled
plasma atomic emission spectrometry (ICP-AES). The main difference between OES and
ICP-AES is the heat source. In ICP-AES, a stream of argon plasma is used instead of
a carbon arc, which increases the temperature significantly, thus eliminating the
elemental spectral crossover experienced with OES. ICP-AES is fairly inexpensive,
reasonably accurate (± 5%), allows a high throughput and requires only a small amount
of material (10 mg). The third method based on optical emission is inductively coupled
plasma mass spectrometry (ICP-MS). It is very similar to ICP-AES, but considerably
more sensitive (often parts per billion are measurable), and considerably more
expensive (Renfrew 1996: 344).
Similar to OES, but focusing on absorption instead of emission is atomic
absorption spectroscopy (AAS). AAS requires 10 mg to 1 g of material which will be
lost in the analysis. It has the advantage of being able to detect light elements
like lithium and sodium and has an excellent accuracy rate of ± 1% for major elements.
However, it is destructive, expensive, slow, and has an accuracy of only ± 15% for
trace elements (Renfrew 1996: 344; Tite 1972: 201).
X-ray fluorescence analysis (XRF) is widely used in pottery analysis,
but can also be used to examine stones like flint. It is functionally similar to UVFA,
but measures emissions in the x-ray (instead of visible) band. There are two types
of XRF: wavelength dispersive (XRF-WD) and energy dispersive (XRF-ED). The latter
is most commonly used in lithic analysis. XRF can be as accurate as ± 2% or as low
as ± 10%. It is very good for identifying major elements, but fails with concentrations
lower the 0.1% (Renfrew 1996: 344-6; Tite 1972: 201-3).
Two related methods, proton-induced x-ray emission (PIXE) and particle
induced gamma-ray emission (PIGME), which are based on ion beam analysis (IBA), can
be used to analyze flint and obsidian. PIXE is very good for examining very small
areas and producing elemental “maps” on a submicron scale. PIGME is very sensitive
to light elements (below sodium) and is often used in combination with PIXE to form
a complete elemental picture. The main drawback to both of these methods is that they
require a particle accelerator (Renfrew 1996: 345-6).
Until recently, the most common method of analyzing flint was neutron
activation analysis (NAA). By bombarding the nucleus with thermal neutrons and
measuring the emitted gamma rays, elements in the sample can be identified. It
requires a nuclear reactor, which is becoming harder to find as more and more research
reactors are being shut down. It usually requires only 10 to 50 mg of material and
is accurate to ± 5% (Renfrew 1996: 345; Tite 1972: 307).
There are several other techniques for sourcing specific types of
lithics. For example, if the sample contains strontium (Sr), lead (Pb) or neodymium
(Nd), the isotopes can be analyzed using mass spectroscopy. Other methods include
x-ray diffraction (jade), cathodoluminescence (white marble), Mössbauer
spectroscopy (iron compounds), and fission-track analysis (obsidian) (Renfrew 1996:
347-50; Tite 1972: 203-4).
IV. Conclusions
UVFA as a tool for lithic sourcing is still in its infancy. Although it
has been applied to material by archaeologists (with varying degrees of success),
there remains no published general reference on its practical use. It has great
promise, in that it is an extremely inexpensive and portable method of analysis.
Furthermore, archaeologists using UVFA locally, on-site, would begin to create the
type of libraries necessary for its more widespread use. Of course, this assumes that
UVFA is actually a viable technique that can distinguish between lithics from
different sources. This must be proven experimentally in the lab before it can be
used in the field.
In my view, the greatest barrier to practical UVFA is the problem of
radiationless transfer of energy and intersystem crossing. It is impossible to
predict exactly how any given material will fluoresce under UV because of the myriad
of possibilities incoming energy has after absorption. The mechanics of which path
an electron “decides” to take to return to the ground state is not entirely understood.
Since photons have many options other than releasing a specific spectra of light,
we cannot guarantee that a given emitted spectra is the “true” spectra of the element
being examined. Work being conducted now by researchers like Hugh Jarvis at the State
University of New York-Buffalo may help to answer some of these questions.
A second problem plagues lithic sourcing in general and is not specific
to UVFA. This is, as Tixier (et. al.) pointed out, that there are many potential
sources of a single kind of rock in any given area. The same rock might have several
outcrops, which are indistinguishable from one another using any technique. Another
problem that concerns lithic sourcing in general is the difference in composition
within the same material. Concentrations of minerals and trace elements can and
regularly do vary within any large sample. For this reason, it might be impossible
to accurately source any raw material based on chemical and optical qualities.
However, the opposite is also true: sometimes the very unique makeup of a locally
available, but geographically ubiquitous material will act as a clear signal to its
source.
In conclusion, UVFA might prove to be a valuable addition to lithic
sourcing, but it is far too early to predict that it will replace older, more
established methods. The most secure method of sourcing lithics remains the good sense
of the archaeologist in applying the appropriate forms of analysis mentioned earlier,
in addition to UVFA, and other archaeological information.
V. Brief Research Proposal
The following is a very brief model for how I will conduct laboratory
analysis of lithic material to be supplied by Dr. James Phillips. Since I do not yet
know the details about the material, the UV lamp, or exactly what sort of preparation
the material might require, this model remains general. The analysis will be carried
out at the Middle Eastern Archaeology Laboratory at the University of Illinois at
Chicago (UIC). The UV lamp will be provided by UIC. I will supply any additional
materials and labor.
Setting up in a large closet or small, windowless room would be ideal,
since I require only a small table and access to power. I intend to build some sort
of a small viewing box, with the light source at the top, in a fixed position, and
a plexiglass shield between the researcher and the specimen. The main purpose of this
is to establish a consistent distance between the light source and the object. I intend
to contact Hugh Jarvis to seek further methodological guidance. I hope to enlist a
friend with some knowledge of photography (or perhaps someone in our department) to
take some slides, assuming that this is not cost prohibitive.
I hope to examine each specimen in four ways. First, I will look at each
major surface under both long and shortwave light. I hope to do the same on a freshly
exposed surface on as many pieces as Dr. Phillips is willing to sacrifice. For each
surface of each piece, I will record the fluorescent intensity (brightness),
saturation (color richness), and hue (shade). I will use a generalized system
described by Earl Verbeek (formerly of the U.S. Geological Survey). The attached
spreadsheet (Fig. IV) details the scheme I will use, which is similar to the basic
system outlined in Jarvis (1995: 7).
If possible, I would like to employ a quantitative method to supplement
the qualitative method described above and in figure IV. This would mean obtaining
use of a fluorimeter, colormeter, or spectrophotometer. Since I have never used any
of the aforementioned, I will have to rely on the help, goodwill, and guidance of
others in putting them to meaningful use. At bare minimum, I intend to use a handheld
photographic lightmeter to measure fluorescent intensity.
Ideally, I would like to look at a range of material before I begin my
analysis. Since I have never done this, I need to see the range of possible (or at
least typical) responses before being able to make qualitative judgments on any
individual piece. If at all possible, I would like to do the analysis over a five
day (Monday-Friday) period. I will write-up the results in a 1-2 page paper with
tables. I am available beginning Monday May 11, 1998.
Bibliography
Becker, Ralph
1969 Theory and Interpretation of Fluorescence and Phosphorescence New York: John
Wiley and Sons, Inc.
Jarvis, Hugh
1995 The Application of Ultraviolet Fluorescence to Lithic Sourcing
Unpublished: Currently in revision, available at:
http://wings.buffalo.edu/academic/department/anthropology/Lithics/uvfa-ms.html[4
]
Lakowicz, Joseph R.
1991 Topics in Fluorescence Spectroscopy: Vol. I-Techniques New York: Plenum Press
Leute, Ulrich
1987 Archaeometry: An Introduction to Physical Methods in Archaeology and the
History of Art Weinheim, Germany: VCH Verlagsgesellschaft mbH
Ostdiek, Vern J. and Donald J. Bord
1995 Inquiry Into Physics, Thrid Edition St. Paul, Minnesota: West Publishing
Company
Rendell, David
1987 Fluorescence and Phosphorescence Spectroscopy Chichester, England: John Wiley
and Sons, Inc.
Renfrew, Colin and Paul Bahn
1996 Archaeology: Theories Methods and Practice London: Thames and Hudson
Schulman, Stephen G.
1977 Fluorescence and Phosphorescence Spectroscopy: Physicochemical Principles and
Practice Oxford: Pergamon Press
Tite, M.S.
1972 Methods of Physical Examination in Archaeology New York: Seminar Press
Tixier, Jacques and Hélène Roche, Marie-Louise Inizan
1992 Technology of Knapped Stone Meudon, France: CREP
[1] UV radiation is often referred to as UV light or the UV band. These terms will
be used interchangeably in this paper.
[2] Fluorescent emissions have four characteristics which can be quantified. They
are energy, lifetime, polarization, and quantum yield (Becker 1969: 76). Depending
on what one is looking for, each is useful. Quantum yield is the most common method
of quantifying fluorescence in archaeology.
[3] Spinning electron refers to the spin angular momentum, sometimes called
vibration of electrons.
[4]
Permission obtained via e-mail to summarize and quote from work on 4/27/98.
Fig. IV
Descriptive (Qualitative) Categories for UVFA & Sample Data Sheet
Brightness
Weak (1)
Medium (2)
Strong (3)
Saturation
Pale (4)
Medium (5)
Deep (6)
Yellow (Y)
Orange (O)
Red (R)
Hue
Violet (V)
Blue (B)
Green (G)
UVFA Data Record Prototype
Date of viewing___________________
Type of material___________________________________
Type of lamp_____________________
Description______________________________________
Corrected (Y/N)_____
Number (if applicable)_______________
Prepared (Y/N)_____
Sample Data (each column will be descrete in actual version)
Short
Ventral Surface
Dorsal Surface
Proximal End
Distal End
Lateral 1 (Left)
Lateral 2 (Right)
Other
Wave-Ext
1-5-G
1-5-G/B
1-5-G
1-5-B/G
1-4-G
1-6-G
Long Wave-Ext
Short Wave-Int
Long Wave-Int