-
Chapter 13
Handheld XRF analysis of Maya ceramics: a pilot study presenting
issues related
to quantification and calibration Jim J. Aimers, Dori J.
Farthing and Aaron N. Shugar
I ntrod uction
The investigation of archaeological ceramics has a long and
varied history with
regard to the analytical instrumentation used (for gcneral
examples, see Peacock
1970; Bishop er al. 1982; Rice 1987; Pollard er al. 2007). In
recent years newer
applications have been used for the analysis of ceramic
materials as wcll, including
rCP-MS (Fenno et al. 2008; Mannino and Orecchio 20 1 I) and INAA
(G lascock
1992; Neff 2000). In most cases the motivation to obtain
chemical concentrations
from archaeological ceramics has been to establish the source of
the clay matrix.
This has proven possible using instrumentation with low
detection limits (i .c. trace
element analysis techniques such as NAA, ICP, AAS, and WD-XRF).
Handheld
X-ray fluorescence spectrometry was developed in the carly
1960's (Piorek 1997)
but did not enter the world of archaeology. outside of isolated
research , until the
early to mid 2000's when the instrumentation became more
affordable (e.g. Uda
et al. 2000; Cesareo et al. 2004; Ida and Kawai 2005; Newman and
Loendorf
2005). With the flourishing use of handheld XRF by non-trained
scientists and
other researchers who may not be trained in the basic (and
advanced) theories of
X-ray fluorescence, its misuse and the misinterpretation of
results is prevalent (see
chapter I of this volume for more detai l).
Several papers have recent ly been published dealing with the
provenancing
of ceramics using handheld XRF with varied success (e.g.,
Morgenstein and
Redmount 2005; Tagle and Gross 2010; Barone et al. 20 I I; Goren
el al. 20 I I;
Speakman el al. 20 I I). Unfortunately, the 'boxed' calibrations
that come with these
instruments are not designed to deal with the complex nature of
archaeological
ceramics . Ceramics are by nature heterogeneous with numerous
components (such as temper) all having variable particle size. They
can have surface alterations and
coatings. and over time, the chemistry of the surface can alter
as well. In addition,
archaeological ceramics often have altered chemical surfaces
related to their burial
environment. Manufacturer calibrations are more geared to modern
applications
and modern materials that are uniform in makeup, and expectjng
calibrations
-
424 Jim J. Aimers, Don J. Fa rthing and Aaron N. Shugar
designed for these purposes to be effective with archaeological
ceramics is
unreasonable. The desire for quantification, whether it be for
provenancing studies or characterization studies , requires the
user to create material specific calibrations
(see Hein el al. 2(02).
This paper discusses current investigations of Maya ceramics
from Belize. The
focus of this study is not to determine the source/provenance of
the clay bodies, but
to investigate the potential for establishing handheld XRF as an
on-site analytical
tool for the characterization and potential classification of
ceramics based on their
chemical signatures. The development of an empirical calibration
is presented
including the process involved in creating reference materials
for that calibration.
Overview of Maya chronology and pottery
The date of the arrival of people in the Maya lowlands is
currently a matter of
debate (see Lohse 2010). but lies somewhere in the Archaic
period (8000-2000
B.C.) with maize pollen indicating farming by about 3000 B.C.
(Pohl er al. 1996).
The Preelassic period dates from roughly 2000 B.C. to A.D. 250
with the earliest
well-documented Maya pottery about IIOO-goo B.C. in the Cunil
ceramic complex
of the Belize Valley (Sullivan and Awe 20 12). By the Late
Preelassic period (often
dated 250 B.C. to AD. 250) Maya pottery was very weU made and
styles were
widely spread across the entire Maya lowlands. Although most of
the significant
cultural aspects of Maya civilization were in place by the Late
Preelassic, the
subsequent Classic period (AD. 250-8(0) is generally considered
the height of
Maya development. The Classic Maya lived in a literate, highly
stratified society
which produced monumental all and architecture and elaborate
polychrome
pictorial pottery. [n tbe Terminal Classic period many sites
were abandoned and
profound changes swept across the Maya world (Aimers 2007b).
Dates vary
because different sites were abandoned or transformed at
different times from
about A.D. 750-1050 but the Terminal Classic has traditionaUy
been dated to about
AD. 800-goo. Pottery of the Terminal Classic varies across the
lowlands but it
was still well-made with an emphasis on elaborate modeling and
incising over
polychromy. The Postclassic period follows the Terminal Classic
and ends at the
arrival of the Spanish in the Maya area at about AD. 1540.
Postelassic pottery also
emphasizes incising and modeling and is typically well-made. The
pottery of the
Postelassic period is the focus here.
-
Handheld XRF analysis of Maya ceramics 425
The Postclassic period and its pottery
Figure 13.1:
N , •
YUCATAN Pt;.NI'SLLA
, , , GU ATEMAL A ".-,. :.
PACIFIC OCEAN
, , I ,
IJI.IrpfqI.Ie • ;- t ....... ,
HOND U RA S
EL SAlVAOQR \,
Map of the Maya region showing key Postdassic and trading si tes
relevant to this study (After McKillop 2(05).
In the early years of Maya archaeology the Postelassic period
was neglected as
a period of cultural deeline following the Classic "collapse" ,
but more recent
research at Postclassic sites has revealed population movement,
innovative
political strategies . increased exchange and commcrciali.mtion
, iconographic
innovation, and intense Mylistic interaction (Smith and Berdan
2000, 2(03). A
key characteristic of the Maya Postelassic period is evidence of
extensive trade ,
especially among sites along the Caribbean coasts and on rivers,
and involving
sites in the northern half of the peninsula such as Mayapan and
Chichen Itza
(Figure 13.1 ). A beller understanding of the economic and
political milieu of the
Postelassic would be greatly aided by more detailed
documentation of the nature
-
426 Jim J. Almers, Don J. Farthing and Aaron N. Shugar
and degree of interaction among Postclassic si tes, and one of
our most informative .rtifact classes is pottery.
(((('//// Lflf./c(
Figure 13.2:
b
/!)//. J)~ J
' /~ )"11 l~ !{IP_ "- j )~~~"'j
,
Red Payil Group Ceramics. Payil Red is the plain type, Palmul
Incised is the incised verSion (aher Sanders 1960: Fig 4, 5).
-
7
Handheld XRF analysis of Maya ceramics 427
Aimers has been investigating the Postclassic period since his
dissertation research
on the Maya collapse and its aftermath (Aimers 2003, 2004c,
2004a, 2007b) and
particularly with research on the pottery of two sites that were
not abandoned in the
Terminal Classic: Tipu (Aimers 2004a: Aimers and Graham 2012a)
and Lamanai
(Aimers 2008 ,2009,20 10; Aimers and Graham 2012b). In the
summer of 2011
Aimers began a pilot study to investigate the chemical
variability of a plain red
type (Payil Red) and a re lated incised type (Palmul Incised)
(see Figures 13.2 and
13.3) using XRF with samples from the inland site of Tipu, and
the site of San
Pedro on the island of Ambergris Caye. These types are not
particularly common
but they are widely distributed in the Late Postela sic period,
and they are much
more common at coastal sites and are thought to have been
produced along the
coast of the Mexican state of Quintana Roo (e.g ., the sites of
Ichpaatun , Tancah
and Tulum, see Figure 13.1; (Sanders 1960: Aimers 2(09). As we
discuss later,
the original goal of the research was to identify compositional
groupings within
these types which might help in addressing trade and exchange in
the Paste lassie
period. We do not expect to link the pots to their production
location except in rare
cases (sec comments below), but we hope that chemical
characterization can help
us map the distribution of pottery types better than surface
style and form alone.
These distributions can help in the construction of inferences
about Maya pottery
production and trade. A larger study is planned to follow the
pilot study with more
stylistic types and samples from more sites.
Figure 13.3: Palmul Incised sherd from San Pedro, Belize,
showing the surface inCISing and the red slip. This example also
has blue pigment which is thought 10 have been distributed from the
site of Mayapan (Mexico).
-
428 Jim J. Aimers, Dori J. Farthing and Aaron N Shugar
Major analytical techniques used in maya pottery studies
In the Maya area, a stylistic classification system known as
type-variety has
dominated the study of pottery since its introduction from
American Southwestern
archaeology in the 1950's and 1960's (Smith , Willey, and
Gifford 1960). Type-
variety organizes pottery hierarchically into wares (based on
broad characteristics
of paste andlor surface). grollps , which are clusters of types
(defi ned by a set of
anributes such as color and decorative treatment). and varieties
which are often
based on single attributes. So, Payi l Red and Palmul Incised
are types within the
Red Payil Group ofTulum Red Ware . Each of these types only has
a si ngle variety
because these types arc macroscopically quite homogenous in
paste and surface
treatment - this is one reason they were chosen for the XRF
study (sce Cecil 20 I 2
for more detail on the pastes, AA data and petrography).
Type-variety has been used widely because it is a rapid and
inexpensive " Iow-tech" way to organize the thousands (sometimes
millions) of sherds that
are produced by excavations at sites in the Maya area (Aimcrs
and Graham 20 12b). Aimers' research to date has involved assessing
interaction among sites
and regions using type-variety analysis of pouery from hands-on
examination of
collections from across the Maya lowlands (see e.g .. Aimers
2004a, 2004b. 2007a.
2008,2009,2010). Type-variety provides a common language for
archaeologists
and has facilitated the compari son of pottery across sites and
regions in addressing
issues as varied as chronology. function. trade/exchange. and
cultural meaning.
Nevertheless, type-variety has been subject to a number of
important criticisms.
One of the most important issues is the characterization of
fabrics (which
Mayanists generally call pastes) at the ware level (Rice 1976).
Paste variation
has been used by some archaeologists as a key discriminating
attribute and thus
uscd to make distinction at the highest (ware) level (e.g .. in
Rice's work cited in
this chapter), but it has been considered by others to be a
minor factor and occurs
randomly in , for example, type or variety descriptions or to
create varieties (Gifford 1976). Attention paid 10 paste has tended
to vary with research questions. Those
interested in manufacture and production. have tended to
privilege paste variation
for the insight it can provide into these issues. Those
interested in consumer
choice, stylistic analysis and comparison, or meaning, have
often considered pa~ l c
variation irrelevant.
Thus. type-variety classification is problematized by
inconsistencies in the
treatment of paste variation that are n01 weaknesses in the
system itself. but result
from the fact that like all classifications, type-varicty
methods vary according 10 the
research questions addressed (A imers 2012a). Still , it is
reasonable for Mayani'"
to seek greater accuracy. consistency. and comparability in the
characterization
-
Handheld XRF analysis of Maya ceramics 429
of paste variation. and the oldest established technique for the
close examination
of paste variation is petrography (Jones 1986. 199 I). Maya
petrographic studies
have been surpri;ingly rare in comparison to work in the Old
World and to the
amount of research on pottery in the Maya area. This is probably
because Maya
pottery is stylistically varied , exceptionally elaborate and
often well-preserved,
so macroscopic characterizations have been adequate for
chronology and broad
comparative studies. Petrography is of course time-consuming and
destructive
which poses a problem with large or complex sample sets.
Petrographic studies
of pottery have tended to focus on issues related to
manufacture. production. and
distribution (e.g .. Rice 1977, 1991 , 1996; Cecil 200lb. 200la;
Cecil and Pugh
2004; Howie 2005; Cecil 2(09). One of the challenges for the
petrographic study
of Maya ceramics is that the geology of the Maya area is
relatively poorly mapped
(see extensive comments about these issues in Howie 2005: 120-
16 I for Belize)
so until more sampling of geology and clays is done it can be
very difficult to
tie pottery to its clay sources. Successful petrographic studies
have tended to be
focused on a fairly local level (e.g .. Cecil and Rices work in
the Pet6n Lakes;
Howie 2005) where the geology is well known or distinctive,
andlor where clay sampling has been undertaken.
Materials science approaches to the study of archaeological
ceramics are
advancing rapidly. Petrography is of course well established,
and recent studies
of archaeological pottery have used XRF (Bakraji el al. 2010;
Bakraji el al. 2006;
Hall 200 I ; Thomas el al. 1992), portable XRF (PXRF)
(Papadopoulou el 01. 2007;
Papadopoulou el 01. 2006; Papageorgiou and Lizritis 2(07),
mineralogical analysis
using XRD (McCaffery el al. 2007; Mitchell and Hart 1989;
Rasmussen el 01.
2009: Stanjck and Hausler 2004; Zhu el al. 2004) , trace
chemistry determination
by NAA (many, e.g. , Glascock 1992; Glascock el 01. 2004;
Hancock el al. 1989;
Lopez-del-Rioelal. 2009; Olin and Blackman 1989),structural and
microstructural
characterization techniques such as SEM (Ownby el al. 2004:
Palanivel and
Meyvel 2010) or combinations of various techniques (Marghussian
el al. 2009;
Padilla el al. 2005; Speakman el al. 20 II) . The best overview
on the use of all
of these techniques in the analysis of archaeological pottery
was done by Rice (1987).
Of the elemental analysis techniques, Mayanists have considered
NAA to
be the most valuable because of its sensitivity, accuracy, few
matrix effects, and
the range of trace elements that can be identified, including
rarc earth elements (Neff 1992:2). The disadvantage of NAA is its
cost and the fact that it can only
be conducted in facilities with research reactors. In addition,
the sample size required for NAA is quite small, typically a small
drilling is all that is required .
For this reason sample heterogeneity could have an adverse
effect on the resulting
I I
-
430 Jim J. Aimers, Don J. Farthing and Aaron N. Shugar
chcmislry obtained. This issue is recognized by reseruchers and
now larger samples are taken and powdered for analysis (see
Speakman el 01. 20 II for example).
Many of the other elemental analysis techniques (e.g., PIXE) are
also expensive
and require equipment that is not easy to acquire. This has led
to continued
interest in petrography and the use of XRF and XRD because many
universities
and museums have access to these instrumental methods. Although
XRD analysis does not provide elemental analysis data insights. it
compliments other techniques
because it provides information on the mineral makeup of
analyzed samples. For example, Tenorio el 01. (2010) used NAA, XRD
, and SEM in a study of pottery
from Laganero, Chiapas, Mexico.
Current trends in Maya ceramic analysis
The introduction of a new and readily accessible analytical
technique typically
results in optimism about its utility for the investigation of
archaeological
problems, For example, Culben and Schwalbe (1987) published an
early study
of the application of standard XRF to Maya ceramics from Tikal
(see al;o
Schwalbe and Culben 1988). This study and others were criticized
concerning
issues of precision and especially comparability of results to
other studies (Bishop
el 01. 1990:543; Neff 1992:4). Recently, ponable and handheld
XRF technology
created a similar wave of optimism but critical evaluations did
not lag far behind.
Shackley (20 I 0) provides the most straightforward critique of
handheld XR F on
issues of reliability and vaUdity as well as the ·'near
religious fervor" with which
the technology ha been embraced by people who are not adequately
familiar
with the methodological and interpretive issues involved (Shugar
2009: also
addresses these issues). This is cenainly the case in Maya
studies. The Mayanist
here (Aimers) learned of handheld XRF relatively recently and
was excited by
what appeared to be a fast way to acquire ·'hard" compositional
data in the field.
Like many others he had no background in XRF methodologies and
no awareness
of the challenges of sensitivity, precision, accuracy, and
comparability of results
using this new technology. This chapter brings together the
differing experience
of the three authors in an investigation of these issues in
relation to archaeological
pottery.
In the study of Maya pottery new analytical techniques. after a
period of
enthusiastic experimentation, are typically absorbed into
research projects which
combine them with more established techniques, In panicular,
petrography
combined with quantitative chemical analysis broadens the scope
of all
investigation to include both the paste makeup (e.g, the
characteristics of the clay
-
Handheld XRF analySis of Maya ceramics 431
body, natural inclusions, and temper which are mOTe indicative
of the Chaine operaroire or specific manufacturing process), and
its particular chemistry (as
stated above - potentially to source clays). Type-variety.
despite its problems, is
also sti ll a very useful organizational and descriptive
structure for Maya pottery.
There is broad agreement that results from multiple techniques
of analysis are
always more useful than anyone alone (Cu lbert and Rands 2(07).
In a discussion
of the challenges of characterizing Aegean pottery Day el al.
(1999: 1034) reached
a similar conclusion:
... different sources of chemical variation emphasize the need
for the
integration of olher information; mineralogical, technological
and stylistic;
which enables the researcher to attribute differences to
provenance or aspects
of clay paste technology. The complex interplay of these natural
and human
SOUIees of variation means that such analyses cannot take place
in isolation.
in a " black-box ,. approach. On the contrary, it is imperative
for mineralogical
and elemental analyses, at least in the Aegean , to be conducted
in an integrated
programme which exploits complementary types of archaeological
and
analytical information.
Pottery variability and the potential of XRF and handheld
XRF
Inter-observer inconsistency is always an issue in type-variety,
especially for
rare types (Aimers 20 12b) but many types, including the ones
discussed in this
chapter, are recognized by experienced specialists with little
if no debate . So , why
is there a need for XRF and other means of compositional
characterization? In the
case of Red Payil Group sherds , the problem is their
macroscopic consistency.
We know that these types are widely distributed and we assume
that like most
widespread types, they were made by multiple producers and
probably at multiple
locations. Pool and Bey (2007:36) note that the "vast majority
of [Maya] pottery
was made and consumed locally" (see also Arnold el al. 1991).
This has been
found repeatedly for Maya ceramics, most famously with the
Preclassic Sierra
Group types which are very stylistically consistent across the
entire Maya
lowlands. This pilot project was designed to see if XRF could
detect intra-type
compositional groups that could be investigated and hopefully
confirmed by
other techniques such as petrography. SEM. and XRD. The
longer-term thinking
was that if standard XRF would reveal compositional groups in
this otherwise homogenous pottery, handheld XRF would have the
potential to do the same. The
ability to use handheld XRF on large numbers of samples in the
field could allow
-
432 Jim J Almers, Don J Farthing and Aaron N. Shugar
the establishment of what are essentially technological
varieties of Payil Red and
Palmul Incised. In some ways, this new portable and handheld
technology could
solve what Aimers (2007a) has called ''The Curse of the Ware" -
the inconsistent
treatment of paste in type-variety (see Rice 1979 for an
extended discussion of this issue).
Another reason for the interest in handheld XRF is that the
ability to export
large number of sherds from Belize, or any country is difficult
at best, making
traditional analysis difficult , and analysis of large sample
groups even morc
problematic. Being able to transport the XRF to the field would
allow for on-site
analysis of the sherds and could help archaeologist direct the
ir research questions ill siw .
Benchtop XRF sample preparation and analysis
To investigate the viability of the XRF as a "discriminating"
tool, a selection
of samples representing the Payil Red and Palmul Incised types
were analyzed
for their major and trace clement composi tions in the
Department of Geological
Sciences ar SUNY Geneseo. All samples were analyzed with a
PANalytical AXIOS
Sequential WD-XRF Spectrometer. The XRF uses a 4 kW Rh-anode
X-ray source
and both a flow and a scintillation detector. The now detector
is ideally suited for the analysis of transi tion clements and the
scintillation detector is ideal for
the analysis of heavy elements. A set of internal curved
crystals (including the
following options: LiF 200, LiF 220, PE 002, and GE III ). are
also used in every
analysis to disperse the X-rays emitted from the sample
according to their different
wavelengths using diffraction. The crystal s are connected to a
turret that rotates to
insert one crystal at a time into the beam path. The crystal
that is selected depends
upon the element that is being analyzed (Table 13. 1). The XRF
is operated at
vollages that range from 10 kV to 60 kV and currents that range
from 10 rnA to
125 rnA. Typically flow detectors and scintillation detectors
have resolutions below
1000 eV, but when used in unison with a crystal spectrometer,
that resolution j",
greatly improved to range from approximately 12 eV (LiF 220) to
31 eV (LiF 2(0) (Jenkins 1999: 1(0).
All pottery samples were cleaned with water and an ordinary
nylon-bristle
toothbrush to remove soil and particulate matter that was
loosely adhered to the
pottery and not considered original to lhe pottery body. The
samples were then
crushed using a SPEX SamplePrep MixerlMili and a hardened steel
grinding
canister equipped with 2 grinding balls. The grinding process
produced a
powder that passed through an 80-mesh sieve size . This was
achieved by milling
-
-
Handheld XRF analy sis of Maya ceramics
e pieces of sample -10 grams of sherd material for 3 minutes.
If. after milling. larg remained . the sample wa, milled for an
additional I to 3 minu
the abundance of large fragments. Between each sample. the
bal
by milling quanz sandbox sand for 3 minutes. The cleaning
san
and the canister was then blown out with compressed air to
femo
sand. Small sized particles are easier to fuse into glass
beads/d
have a greater amount of surface area and dissolve easier in
th
Small and even particle sizes are also essential for
preparing
because the small and even-sized particles are easier to hom
compact into a morc coherent Hat-faced pellet with no major
n
the sample surface. Both fused beads and well-made pressed
pe
for obtaining the best possible XRF analysis because they
mininu
which can skew the data and not accurately represent the
overa
sherd. The powdered materials are also in the ideal form for
(XRD) analysis and samples can be analyzed first with XRD an
tes depending on
I mill was cleaned
d was disposed of
ve any additional
isks because they
e fusing process.
compacted pellets
ogenize and will
icks and divots in
lIets arc essential
. ze matrix effects,
II chemistry of the
X-ray diffraction
d then the powder
can be re-used in the preparation of XRF samples.
Cry~lal name PANal)'lical's o;;ugge~tions for use
LiF 200 crystal Used for routine analysis for elements
LiF 220 crystal Used for routine analysis for elements is not as
reflective as the LiF 200. but h effect.
Upgrade 10 PE (002) curved crystal Used for e lements between AI
and CI
Ge ( Ill ) curved crystal U.sed for P. S and CI
PX I synthetic multilayer cl)Mal Used for elcmenls bet ween 0
and Mg
Table 13.1 XRF analyzing crystals and their suggested uses
during analysIs.
ranging from K 10 U
bel wcen V and U. It as a highcrdi
-
434 Jim J. Aimers, Don J. Farthing and Aaron N. Shugar
automated fusing machine, the crucible was evenly heated to ....
IISOoe, mixed
well (while avoiding the creation of bubbles) , and then the
molten mixture was
poured into a platinum mold. When cool, the resultant glass bead
was analyzed
with a PANalytical AXIOS XRF. The analytical program, IQ+ used
internal
standardization to quantify the element concentrations. The
initial standardization
was based upon fundamental parameters that were improved by
analyses of laboratory-generated standards containi ng known
amounts of major elements (the
IQ+ suite). The initial standardization is regularly checked by
weekly analyses
of two glass monitor standards (BGSMON and AUSMON-F) as well as
the
occasional analysis of an in-house set of geological samples
which allow us to
monitor for drift , background levels and quantitative accuracy.
The two glass
monitor samples came with the XRF. AUSMON-F is a drift monitor
standard that
was specifically chosen to coordinate with measurements of sil
icate materials and
is avai lable through multiple vendors including Analytical
Reference Materials
International and Brammer Standard. Our current accuracy for
major elements is,...
± I wt.% for high concentration major clements. After every
analysis we manually
inspected each spectrum to make sure that the "search-and-match"
function of the
analytical program identified all the peaks. We also force the
analytica1 program to
strips Br from the results. Sr is a constituent of the nux and
is never considered as
a major element. Sr must be stripped from the analysis because
it interferes with
the aluminum peaks; the position of the bromine L-lines at
1,480.4 eV overlap
with the aluminum K-lines located at I ,486.3 and 1,486.7 eV.
Since the quantity
ofBr in the sample was known, stripping it from the spectrum was
trivial and did
not have a detrimental effect on the AI analyses. Glass beads
are ideal materials
for major element analyses because they are extremely homogenous
and wil l not
generate analytical errors due to grain sizes or preferential
grain orientation as is
the case when mica or clay is present Isee Jenkins e1 al. (1995)
for a discussion of
grain-size related errors I. In general, the concentration of
any element as it relates to the intensity of the X-ray peak is
mathematically described as:
(I)
C represents the concentratjon of a specific element , K is the
calibration constant
determined from the analysis of standards, 1 is the intensity of
the peak and M
is a correction factor that accounts for matrix effects. The M
value accounts and
corrects for a variety of parameters including particle size,
particle size distribution.
crystallographic nature, and grain orientation (see Rousseau
2006 for insight on
the calculation for M). 1n this simple equation , M is
potentially the greatest source
of error because of the variety of parameters it incorporates.
Vitrifying a sample
-
Handheld XRF analysis of Maya ceramics 435
simplifies the calculation of M, thus strengthening the
certainty associated with
the resulting concentration measurement.
Even though glass beads minimize matrix effects, they were not
used for trace
element analysis. The preparation of glass beads is a dilution
process, making them
not ideal for trace element analysis due to the low
concentrations of the elements
being studied. Trace element data were obtained on pressed
pellets instead of
glass beads. Pressed pellets were prepared by combining 6 ± 0.00
I grams crushed
sherd (using the same crushing techniques described above) with
I ± 0.001 grams
cellulose binder (PrepAid Cellulose Binder (C,H ,,o,l. from SPEX
CertiPrep).
The mixture was homogenized and then pressed into a pellet using
a steel die
and plunger set. The mixture was pressed with a hydraulic press
at 25 tons for 15
minutes and then the pressure was slowly released over a
I-minute timeframe to
avoid cracking the disk. Pressed pellets provide a concentrated
amount of material
that is well homogenized and flat, which is importalll for
obtaining a correct
analysis. Changes in sample neight will shift the location of
peaks on the energy
spectrum. Once the data is collected, it is quantified by
comparing the analysis
to blank monitor standards (to account for drift), synthetic
calibration standards
(which create the empirical foundation for the analysis), and a
set of geological
standards (which help improve the initial standardization). The
primary foundation
for the trace analysis is a set of synthetic standards that work
in conjunction with a
software system that I) defines the background values around the
analytical peak
locations, 2) accounts for peak interactions (as was the case
for Sr and AI in the
major element analysis) and 3) accounts for matrix parameters in
the standards.
Detection limits vary by element but are reported to range
between 0.4 ppm to
1.3 ppm for many of the elements of interest (Sr and Y at 0.4,
Rb at 0.6, Zr at 1.1
and Nb at 1.3; Jenkins 1999: 119) (see Table 13.2 for trace
element results).
The geological standards were prepared in the SUNY Geneseo XRF
laboratory
using the same techniques described above. These standards are
widely used by
the geological community and supplied by the United States
Geological Survey
(see Wolf and Wilson (2007) for a brief overview of the USGS
Standards
program). The set of standards used at SUNY Geneseo was chosen
because they
best represent the variety of samples analyzed by their XRF
facilities. Should this
pilot project become more substantial, the potsherd analyses
would benefit and
be improved by using ceramic standards that might better
represent the nature (in terms of mineralogy and matrix) of the
Maya pottery and our initial analysis can
be re-calculated based on the improved standardization.
-
436 Jim J. Almers, Dari J. Farthing and Aaron N. Shugar Handheld
XRF analysis of Maya ceramICS 437
Sample' Sc V C, Mn Co Ni CU Zn G. As B, Rb S, Y Zr Nb Mol Cd Sn
Sb I Co; ! Sa La Cc Nd Sill Yb Hf Tai w i Pb Th U
TI 32 39 60 79 3 13 5 53 8 0 3 4 134 23 157 7 2 8 9 3 II 3 220
48 114 47 7 0 3 2 8 14 9 3
T2 29 74 55 255 6 23 13 55 13 4 2 84 67 25 155 13 025 5 II 3 9
10 362 24 57 27 3 0 3 3 12 16 I I 3
T4 32 48 65 172 3 14 4 52 9 5 3 6 139 23 224 10 2 6 I I 3 10 2
279 37 84 34 5 0 4 2 10 17 II 2
T5 30 41 57 58 2 15 4 82 9 3 3 4 120 30 160 8 I 7 9 2 9 0.08 235
75 156 67 12 0 4 2 8 17 9 2 -
n 27 62 52 315 5 25 I I 81 10 3 7 5 1 134 31 212 16 0.34 8 10 3
7 6 377 33 71 32 6 0 7 2 10 22 II 3 -T8 27 44 69 217 3 16 5 100 10
0.47 3 4 114 19 225 9 2 I 9 3 7 2 276 3 1 72 28 5 0 6 3 10 17 10
2
T9 23 62 55 216 5 27 14 99 13 3 I 54 108 30 195 15 0.18 2 II 2 5
3 369 32 65 30 8 0 4 3 13 19 12 2
TIO 43 31 29 464 5 18 5 29 4 0 I 6 69 13 70 2 0.44 5 9 6 12 5
213 18 47 10 9 0 3 2 4 9 5 ~ TI2 34 45 6 1 354 3 17 5 67 9 9 2 6
124 21 193 8 2 4 8 2 7 3 202 47 96 38 8 0 5 2 8 16 9 3
TI3 28 46 75 153 2 16 6 56 10 3 5 12 220 25 249 II 3 3 9 3 10 6
253 47 101 44 9 0 6 2 13 19 13 3
T I4 26 SO 9 1 324 3 24 9 7 1 II 4 5 12 252 35 294 12 2 2 8 3 II
2 265 42 74 33 6 0 6 2 12 21 15 3
TIS 27 43 65 156 2 18 7 110 10 4 3 8 85 15 206 9 3 5 8 I 7 0.95
175 2 1 5 1 22 3 0 4 I 10 16 9 2
TI6 26 72 58 725 8 26 13 93 II 2 4 61 136 3 1 202 14 0.67 5 9
0.73 4 6 360 38 70 32 7 0 5 2 10 25 II 3
T I7A 0,05 II 0 58 4 7 0 51 II 6 2 55 59 17 121 9 0.39 4 II 5 6
0 0 0.07 4 3 7 0 5 2 6 14 10 3
T I7S 0.05 II 0 .92 63 4 7 0 52 I I 2 I 57 62 16 124 9 0.53 6 II
4 9 0 0 0.08 9 2 0 0 4 2 4 14 10 3
TI8 022 2 0 53 2 6 0 60 9 2 3 53 97 18 113 8 027 6 I I 3 7 022 0
0,7 10 2 17 0 3 3 I 13 10 2
SP I 0 I I 0. 1 14 I 7 0 26 7 6 5 5 456 13 148 6 2 2 9 2 8 I 0.9
0 19 0 0 0 3 3 4 I I 10 5
SP2 0 .47 0 0 II 0 7 0 30 8 7 7 7 4SO 19 136 7 2 6 9 2 I I 17 0
0 25 6 0 0 3 6 5 15 10 4
SP3 0.37 2 0 II 5 II 0 41 10 I 9 5 449 18 166 9 3 I 7 2 6 0 II 0
10 0 0 25 5 0 0 16 12 5
SP4 0.05 7 2 17 2 5 0 28 8 7 5 8 592 18 185 7 3 5 10 2 II 0 0
0,09 4 I 6 0 5 2 2 13 12 8
SP5 0.05 6 0.89 17 2 4 0 28 6 5 4 8 453 20 137 6 2 7 9 4 12 0 0
0.08 5 2 3 0 3 2 2 II 10 4
SPG 0.32 6 0 II I 5 0 41 8 8 II 7 330 20 156 7 3 5 8 0.64 7 I
0.06 0 8 4 0 0 3 2 2 15 10 5
SPB 0.05 I 0 17 0 7 0 27 8 5 5 6 362 15 148 7 2 5 9 0 8 0 0 0 8
I 5 0 4 0 8 13 9 5
SP9 0.05 3 0.32 14 I 4 0 3 1 7 6 10 8 394 16 184 7 I 4 10 3 7 0
0 0 8 3 3 0 5 4 3 14 10 5
SPIO 0.05 3 0 0 0 4 0 36 10 5 4 8 255 2 1 184 9 3 5 I I 4 8 0 0
0.04 85 15 0 0 4 I 3 18 10 4
SPII 0.05 0 0 10 0 5 0 39 8 8 13 7 388 17 185 8 2 3 9 3 9 0 0
0.55 7 0 0.03 0 6 2 2 16 10 8 .-SP I2 0.05 5 0 39 3 9 0 33 9 9 3 II
387 21 236 9 2 5 9 2 8 0 0 0 7 0 0 0.3 1 5 4 4 17 13 6
SP I3 0.05 3 0 13 I 5 0 45 10 6 8 6 363 17 213 9 0.98 5 10 5 7 0
0 028 8 2 4 0 6 I 0 15 II 4
SP I4 0.04 0 0 30 13 7 0 37 10 5 9 10 348 17 2 12 9 2 7 9 2 10 0
0 0 38 37 10 6.37 5 5 0 14 I I 9
SPI5 0.05 I 0 3 I 3 0 40 10 4 14 8 479 19 165 9 3 6 10 2 7 0 0
0.04 69 0 0 0 4 0.78 4 16 II 6
SP I6 0.1 0 0 II I 9 0 ISO 10 5 6 8 504 14 182 9 2 7 12 3 4 0,03
0.04 0 0 0 2 0 5 0 2 25 I I 5 . -
SP I7 0 .1 4 0 0 57 2 17 0 50 14 8 6 II 400 36 33 1 15 +--SP I8
0.12 0 0 12 3 8 0 29 8 4 6 6 469 16 14 1 7
3 6 10 3 6 029 0 0.07 10 2 0 0 7 2 13 26 18 5
3 I 8 3 II 0 0 0.33 17 4 2 0 3 0 9 15 II 5
SP I9 om 0 0 80 4 9 0 46 12 9 9 14 499 32 304 13 3 5 9 3 6 0 0 0
10 0 3 0 8 0 4 23 17 5 -SP20 0.05 4 0 74 2 I I 0 5 1 14 7 6 14 329
28 335 14 3 6 10 3 7 0 0 0 13 8 0 0 8 4 7 26 16 5
- -
Table 13.2: Trace element analysis of pressed pellets by
panalytical XRF Resuhs are in ppm.
-
438 Jim 1. Almers, Dori 1. Farthing and Aaron N. Shugar
Handheld XRF sample preparation and analysis
Samples of sherds were prepared by both abrading sections using
a silicon carbide
grinding paper and by scraping the surface with a stain less
steel blade (Q remove any accretions , surface decoration or slip
to ensure the bulk matrix of the ceramic
body was exposed. The surface was flattened to simulate the flat
smooth samples
prepared by fusion and pellet methods and ranged in size from
approximately
I cm2 to 1.5 cmz. Samples were cleaned with an air compressor
blast prior to analysis. Analysis was conducted using a Bruker
handheld Tracer lIl -SD XRF
spectrometer with an Rh tube and a SOD with a resolution of -
145 eV. Instrument
setting for high Z elements were 40 kV at 20 flA using an AI Ti
Cu filter (thickness
of 150 !Ull copper, 25 !'Jll Ti and 300 !'Jll AI) producing
valid count rates between
7000 - 9000 cps for between 500 - 600 seconds. Data was analyzed
using Bruker
SPIXRF software.
Values obtained from the bench top XRF for trace element
analysis from the
pressed pellets were used to create an initial calibration using
Bruker S I Cal Process based on Compton normalization in
conjunction with empirical calibration . The process used was
similar to that by Smith (Chapter 2 this volume) and Ferguson
(Chapter 12 this volume). The limiting factor was that the data
for major light
elements that were being calculated from the fu sed bead samples
were not
avai lable at the time of calibration so the relevant elements
(A I, Si, P, S, K, Ca. and
Fe) were not calibrated for in this initial study but will be
included in the second
round of testing .
The instrument setup for measuring these low Z elements is 15kV
and 55 flA
under vacuum with no filter. Potentially a 25.4 !'Jll Ti filter
could be used, and
might be thought of as the right filter to use si nce it wou ld
absorb the L lines of
Rh avoiding any peak overlap in that region of the spectrum (i
.e . CI Ka - 2.6
keY). In fact, using no filter provides a better assessment of
the lighter elements
present. The L lines of Rh enhance the detection of elements
with binding energies
just below that of Rh La (2 .69 keY). This enhances the
detection of AI, Si. P.
and S (1.48 keY, 1.74 keY, 2.0 keY, 2.31 keY respectively; see
Figure 13.4 for
comparison) . This initial testing indicates that when
additional data from the
bench top XRF is made available, a similar process for
calibration (as described
for the trace elements) wi ll be successful.
Determining the limits of quantification using this methodology
for our sample
set has not yet been undertaken. This is due to the limited
number of .am pies
we have to look at and the restricted range of concentrations
for each element
of interest. As the database continues to grow, a more complete
study will be undertaken to provide an accurate assessment of the
quantification potential. That
-
Handheld XRF analysis of Maya ceramics 439
being said, the limits of detection achieved using a WDS crystal
spectrometer (see
above) are nOl possible with a silicon drift detector (SDD) ,
Although the SDD has
a bener resolution than a Si-PIN detector (-145eV vs -200eV
respectively), this
is approximately 10 times the resolution of the WDS system.
There is inevitably
some peak overlap that will not be able to be resolved . In
addition , WDS systems
have a bener baseline which improves their detection limit.
Previous work on
similar Mesoamerican ceramics have shown detection limits as low
as 4 ppm
(Tagle and Gross, 20 10) but a more realistic value for the
limit of quantification
may be closer to 10 - 14 ppm as found by Speakman el 01. (20 II
). This of course
varies by element. but provides a rough idea of the potential
level of quantification
attainable using the handheld XRF. Both of these previous
studies used a Tracer
Ill-V) which has a Si-PIN detector and quantification of this
level should be
considered reasonable for the SOD detector as well. (For more
discussion on
the determination of the limits of detection and quantification
see Thomsen and
Schatzlein and Mercuro 2003).
-• j
• . " ~ -..- -
Figure 13.4: Spectra of light element analysis uSing a 25.4 ~m
Ti filter (grey line) versus using no filter (black line) (TRACER
11I·5D Rh lUbe 15 kV. 55 ~A With vacuum for 180 secs).
The high Z element calibration was able to obtain values for a
wide range of other
elements outside the low Z ones mentioned previously. Thc cali
bration file was
created in two parts . one for the identification of the major
high Z elements with
other elements that have a direct effect on either peak overlap
or slope correction
(Sr, Y, Zr, Nb. Mo, Cd, Sn and Sb) and the other for the
identification of the
remaining high Z elements (see Table 13.3). The general matrix
of the ceramic
appears to be comprised of Ca, Fe, Sr and Zr as these four
elements have the
-
440 Jim J. Almers, Dori J. Farthing and Aaron N. Shugar
strongest Ka, peaks (see Figune 13.5). These matrix elements are
included in
both calibrations to help account for both elemental peak
overlap as well as slope
corrections.
All clements Element .. used Elemenb u~d found In
for Call for Cal2 samples
All elements Elemenb u~d Elements used found in
for Call for Cal2 sample~
CaKa C.,Ka CaKa AsKu AsKa
"nKa TiKa BrKa VKa V Ka {,bLP I'bL~
CeL~ CeL~ ThLa ThLa
CrKa CrKa RbKu RbKa NdL~ , NdL~ SrKa SrKa SrKa
MnKa MnKa YKa Y Ka YKa
FcKa FeKo FeKo. ZrKa Z
-
Handheld XRF analysis of Maya ceramics 441
..
•
Figure 13.5: Spectrum of sample SP01 showing the major elements
being Ca, Fe, Sr, and Zr (TRACER 111-SD Rh tube 40 kV, 20 mA with
279 mm AI, 2S.4 mm Ii. 6mm Cu filter collected for 600 secs) .
........
7"-'~-ll'·o.&!i1.
. .. • /' • L ..
"
Figure 13.6: Plot of benchtop XRF and handheld XRF data for
Strontium shOWing an R' of 0.8574.
Figure 13.7:
, .
/ . ~ ..
Plot of benchtop XRF and handheld XRF data for Zirconium shOWing
an R' of 0.8744
-
1I(l~
I O '" Qj 3 Q: 5. ~ I'D ::r o::w 5:~' ~ x'" ~g--:--nl' ~
I ::> :;. '" ~ ::> ,., ". o
"0 X co ~
'" ::> "-:;. '" I '" 5. ".
'" a: x co ~
@
" :l;' ::>
" ". o "0 X co -~ I
Sample
SP1
SP2
SP3
SP4
SP5
SP6
SP8
SP9
SPIO
SP1 2
SP13
SP14
SP15
SP1 6
SP17
SP18
SP1 9
SP20
T1 7B
B H B H
Mn Zn
14 22 26 15
11 7.6 30 21
11 0 41 100
17 17 28 17
17 13 28 29
11 21 41 40
17 18 27 12
14 21 31 31
0 0 36 41
39 38 33 19
13 24 45 46
30 29 37 88
3.1 2.7 40 40
11 18 150 150
57 58 50 49
12 18 29 29
80 80 46 46
74 74 51 51
63 63 52 0
B H B H B II B H
Ga Th Rb S,
7.0 6,7 10 10 53 5.4 456 457
83 7.6 10 10 7,1 6.5 450 446
10 10 12 12 4.8 6.1 449 435
83 6,8 12 11 8.1 8.0 592 544
6.4 6,1 10 10 8,2 7.0 453 426
7.7 7.4 10 10 7,2 7.7 330 358
7.8 7.8 9.4 10 6.1 6,4 362 337
7.0 7.5 10 11 7.9 83 394 375
10 10 10 10 8.0 8.1 255 255
9.5 10 13 12 11 10 387 386
10 10 11 10 5.6 5.5 363 257
10 10 11 12 10 10 348 348
10 10 11 11 7.5 7,1 479 44 1
10 10 11 11 8.5 9.1 504 407
14 14 18 17 11 11 400 449
8.2 8.0 11 10 63 5.5 469 369
12 12 17 17 14 13 499 500
14 14 16 16 14 14 329 328
11 13 10 9.4 57 42 62 93
B H B II B H B H
Y Z, Nb Mo
13 15 148 130 5,9 5.9 1,7 1,8
19 20 136 124 6.9 6.7 2.5 1.9
18 18 166 180 8,6 8.9 3.0 2.0
18 18 185 11 0 72 73 2,6 2.1
20 17 137 112 5,9 6,1 1,7 1,7
20 23 156 158 7.1 7.7 3.0 2.0
15 15 148 155 6.8 6.8 1.8 2.0
16 16 184 182 7,4 7,4 1.0 2.0
21 20 184 184 8.9 7,7 2,8 1,9
21 20 236 222 9.2 9.0 2.1 23
17 15 21 3 207 9.5 7.9 0.98 2.0
17 17 2 12 212 93 10 22 2.0
19 19 165 154 8.8 8,4 2,6 21J
14 14 182 182 8,8 8,7 1.6 2.0
36 35 33 1 339 15 14 3.1 31J
16 17 141 140 6.9 6.8 3.1 2.0
32 32 304 304 13 13 2,6 2,8
28 28 335 335 14 13 3.1 2.8
16 23 124 183 8,9 8.0 0.53 1.5
B H B
Cd Sn
23 3.8 9.5
6.2 3.6 9.1
0.6 6.6 7,1
5.4 8.7 10
6,7 3.4 9,2
4.7 3.5 7.6
4.9 2.4 9.1
4.2 3,7 10
4,8 4,7 11
5.2 4.2 93
4,7 2.1 10
6.6 71J 93
6.1 4.0 10
6.9 6,8 12
5,6 5,6 10
1.1 21J 8.4
5.5 5.5 8.9
5.7 6.1 10
5.6 2.0 11
H
10
10
10
7.4
10
9.5
10
9.4
10
10
10
10
10
9,4
10
10
91J
10
10
B H
Sb
23 1.8
2.4 1.5
1.7 32
2.0 7.4
3,9 3.0
0,6 13
0.0 1,4
33 2.5
4.0 -0.1
2,4 2.5
4.8 2.4
1,6 1.6
1.9 1,7
3.4 4.2
3.0 3.0
3.0 3,6
2.5 5.2
35 33
42 2.5
t '-'
~
3 >->-3 '" i" ~ >-Ql' 5-~.
'" ::> "-~ i3 ::> ;Z V> ". C
-
Handheld XRF analysis of Maya ceramics 443
Although good correlation exists with some elements there are
those that arc better
correlated than others (Table 13.4). It is possible that some of
these elements might
be better calibrated when investigating the low Z elcments (i.e.
Sc, Ti , Ce, V, Nd,
Cr, and Mil) and attempts will be made to do some to improve the
correlation. During the next phase of this study multiple sample
locations will be run on each
sample to establish the methodology's precision.
Conclusions
The inherent issues related to XRF analysis of ceramic sherds
without major
pre-treatment are becoming understood by researchers today. III
this particular case, the homogeneity of the ceramic matrix offers
a unique opportunity to use
handheld XRF for chemical characterization. Where there has been
success in
calibration of handheld XRFs for other purposes, the intention
of collecting data
for provenancing purposes is still questionable (Speakman ef af.
2011) and the
issues complicating this matter may never be resolved. At this
point of time. for this study, it appears that we have good
correlation of data and it is expected that
we can only improve as we expand the range of elemental
concentrations used for
calibration.
The honeymoon between archaeological ceramic specialists and
handheld
XRF may be ending, but the relationship shows promise. The work
described in
this chapter is a step toward establishing standard methods for
the use of handheld
XRF with archaeological ceramics and calibration with benchtop
XRF. It is still
too early to comment on some ofthe broader cu ltural questions
about Maya pottery
production and exchange discussed earlier, although the results
of the calibration
work are reason for optimism that handheld XRF can be a valuable
tool in this
research, which will ultimately require a range of analytical
approaches. Research
questions that require methods as diverse as type-variety and
XRF demand
collaboration between specialists with different backgrounds and
we hope this
chapter is an example of the value of such collaboration.
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