chapter 13 handheld xrf analysis of maya ceramics: a pilot...

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


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


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


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


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


..

•

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


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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