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Study of archaeological ceramics by total-reflection X-ray fluorescence

spectrometry: Semi-quantitative approach

R. Fernndez-Ruiz a,, M. Garca-Heras b, c

a Universidad Autnoma de Madrid, Facultad de Ciencias, Servicio Interdepartamental de Investigacin,

Modulo C-9, Laboratorio de TXRF, Crta. Colmenar, Km 15, Cantoblanco, E-28049, Madrid, Spainb Instituto de Historia-CSIC, C/Serrano, 13. E-28001, Madrid, Spainc CENIM-CSIC, Avda. Gregorio del Amo, 8. E-28040, Madrid, Spain

Received 28 December 2006; accepted 24 June 2007

Available online 23 August 2007

Abstract

Total-reflection X-ray fluorescence spectrometry has been compared with Instrumental Neutron Activation Analysis in order to test its potential

application to the study of archaeological ceramics in the archaeometric field. Two direct solid non-chemical sample preparation procedures have been

checked: solid sedimentation and solid chemical homogenization. For sedimentation procedure, total-reflection X-ray fluorescence allows the analysis

of the elemental composition with respect to the size fraction but not the average evaluation of the composition. For solid chemical homogenization

procedure, total-reflection X-ray fluorescence provides precise (from 0.8% to 27% of coefficientof variation) and accurate results (from 91% to 110% of

recovery) for 15 elements (Cr, Hf, Ni, Rb, Al, Ba, Ca, K, Mn, Ti, V, Cu, Ga, Y and Fe) with an easy sample preparation process of the solid clay and

without previous chemical treatment. The influence of the particle sizes has been checked by total-reflection X-ray fluorescence sample angle scans and

anomalous behaviors have been found for three additional detected elements: As, Sr and Zn, which can be attributed to interference effectsof the mineralgrain sizes of their associated chemical phases in the total-reflection X-ray fluorescence interference region. The solid chemical homogenization

procedure produces data useful for archaeological interpretation, which is briefly illustrated by a case-study. Finally, the decantation procedure data can

be also useful for size chemical speciation and, consequently, for alternative environmental total-reflection X-ray fluorescence applications.

2007 Elsevier B.V. All rights reserved.

Keywords: TXRF; INAA; Archaeological ceramics; Size fraction; Compositional characterization

1. Introduction

The determination of the composition of ancient ceramic

samples has a special relevance to the construction of heuristicmodels concerning the production and distribution of these

materials in the past. Currently, this kind of study constitutes

about one third of all archaeometric research that is carried out

on an international scale [1]. Since the 1970s, the analytical tool

most often used and accepted for the archaeological community

has been INAA, because of its ability to provide the required

levels of accuracy, precision and detection limits for its

application in archaeological ceramics studies. The largenumber

of analyses already performed by several INAA laboratories also

provides an important data bank which can be compared with

new information from emerging techniques. Nevertheless, the

wide use of this analytical method has not yet overcome, in some

cases, drawbacks such as high cost, or difficulty of access to a

suitable nuclear reactor for sample irradiation [2]. As alter-natives, less expensive and more accessible methods have been

employed such as traditional XRF, AAS or ICP-OES. One of the

challenges facing current archaeometric research on ceramics is

the intra-regional differentiation of pottery production centers, a

subject that requires large and accurate sets of data on the

composition of ceramics. Therefore, the establishment of new

analytical tools or the development of those already proven

requires both correct standardization and normalization with

international accepted analytical techniques, such as INAA, in

order to assure the validity of the analytical results [35].

TXRF main features and potential applications can be found in

the paper of Prange [6] or the excellent book of Klockenkmper

[7]. Previous investigations, carried out by Klockenkmper et al.

Spectrochimica Acta Part B 62 (2007) 11231129

www.elsevier.com/locate/sab

Corresponding author. Fax: +34 914973529.

E-mail address: [email protected] (R. Fernndez-Ruiz).

0584-8547/$ - see front matter 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.sab.2007.06.015


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[8], Cariati et al. [9] or Fernndez-Ruiz et al. [1012], were the

departure point for this investigation. The best approach to the

ideal TXRF thin film criteria for a solid particle deposition is that

the following three fundamental requirements are fulfilled: (1)

chemical homogeneity of the solid particles, (2) average particlesizes around 1 m and lower than 10 m [13], and (3)

homogeneous spatial distribution of the deposited particles on

the sample carrier.

To provide the TXRF validation for this type of studies, a

reference clay material analyzed routinely by INAA was

employed as reference material, Ohio Red Clay from Resco

Products, Inc, Oak Hill, OH, USA (Ohio Red Clay-2 hereafter).

This sample was habitually used as batch control by the team of

the University of Missouri-Columbia in their INAA analyses

[14]. This work presents the results obtained in the comparison

of both techniques (INAA and TXRF) for the Ohio Red Clay-2

reference sample and also, the investigations carried out for thesamples preparation and optimization for TXRF analysis. The

application of the final TXRF procedure developed was applied

for evaluating a real archaeological case.

2. Experimental section

2.1. Instrumentation

Three main techniques have been used in this work. TXRF

for the analysis of the samples; quasi-elastic light scattering

spectroscopy (QELS) for the determination of the distribution

of particle sizes in suspension of the analyzed samples and

scanning electron microscopy (SEM) for the investigation of the

final size, distribution and homogeneity of particles deposited

on the flat carrier.

The analysis by TXRF was performed by using a Seifert

EXTRA-II spectrometer (Rich Seifert & Co, Ahrensburg,

Germany), equipped with a molybdenum X-ray fine focus

lines, and a Si(Li) detector with an active area of 80 mm2 and a

resolution of 157 eV at 5.9 keV (Mn K

). The measurements

were performed working at 50 kVand filtered with a 50 m Mo

foil, adjusting the intensity so that a count rate of about 5000 cps

was achieved and an acquisition time of 1000 s. TXRF 8030C

spectrometer (Cameca, France) was also used with the objective

of undertaking studies of angular dependence of signal intensity

for some elements. This spectrometer combines a 3 kW X-raytube with a Mo/W alloy anode with a W/C double-multilayer

monochromator and in addition allows the variation of the

incidence angle by tilting the sample holder unit.

The QELS system used in this study was the AutoSizer IIc of

Malvern Instruments Ltd., equipped with a HeNe 5 mW laser,

a photo-multiplier and a processing electronic system controlled

by the Malvern AutoSizer computer package. The SEM

equipment used was the Philips XL-30 equipped with a W

source, detectors of secondary and backscattering electrons and

a vacuum working lower than 4104 Pa.

2.2. Procedure of sedimentation

2.2.1. Samples preparation

Keeping in mind the three main requirements mentioned in

the Introduction section, and as a first approach to the problem,

it is possible to obtain different clay size fractions by the

sedimentation method. Three sets of samples (5 samples each)

were prepared from the Ohio Red Clay-2 reference sample.

First, the sample was ground for 30 min in an agate mortar.

Then 100 mg of the ground sample was poured into a test-tube

and mixed with high-purity water (Milli-Q, 18.2 M) up to

10 ml. Next, the test-tube was placed in an ultrasonic bath for

30 min in order to disaggregate and homogenize the sample.

Once this process was carried out, the sample was left to settle

for 12 h. Finally, aliquots of 1 ml were taken, measured from the

base, at three different depths (15 cm in Set-1; 10 cm in Set-2;

and 5 cm in Set-3) in order to obtain an average distribution of

different particle sizes (always lower than 10 m and with an

average size around 1 m as postulated in the second main

requirement). Thus, the following three particle size sets were

obtained: Set-1, lower than 2 m; Set-2, between 0.05 and

5 m; and Set-3, between 0.1 and 10 m. Fig. 1 shows the three

size distributions obtained by QELS.

From 2 to 5 l of each fraction of particles was deposited on

a quartz sample support and dried on a ceramic hot plate. All

manipulations were made in an A-100 class laminar flowchamber.

2.2.2. Results and discussion

In these conditions the samples were analyzed by TXRF.

Link Analytical AN-10000 computer package was used to

deconvolute the registered spectra. Once the element areas were

obtained, they were converted into relative mass units using the

equation

mx mFeSFeAx

SxAFe1

where m is the relative mass of a given element, A is the peak

area, S is the relative sensitivity and the index x and Fe denotes

each element analyzed and element chosen as referenceFig. 1. QELS spectra of aqueous sample distribution of Set-1, Set-2 and Set-3.

1124 R. Fernndez-Ruiz, M. Garca-Heras / Spectrochimica Acta Part B 62 (2007) 11231129


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respectively. The Svalues are known since they were measured

by means of standard solutions, while the rest of the parameters

are experimental ones [12].

TXRF analyses were performed for the elements As, La, Nd,

U, Co, Cr, Cs, Hf, Ni, Rb, Sc, Sr, Zn, Al, Ba, Ca, K, Mn, Ti, V,

Si, Cu, Ga, Y and Fe. From the 25 elements evaluated, a total

number of 18 were chosen for routine analysis. Si was rejected

because the sample support was made of quartz, which involved

a Si random rise which was difficult to quantify. This fact could

be avoided by using plastic sample supports. Nonetheless, it

was preferred to use a quartz sample support due to its lower

background contribution. Co was also rejected because, in this

case, it was seriously interfered by the high intensity of Fe K

lines signal. La, Nd, U, Cs and Sc were rejected because they

were close to the detection limits that TXRF presents for this

matrix.

A relative mass value of 100 was associated to the Fe signal

(mFe). Fe was chosen because it is always present in clays and

ceramics of archaeological interest and it usually shows a

clearly differentiated peak in TXRF spectra as Fig. 2 shows.

The results of the Ohio Red Clay-2 reference sample

analyzed by INAA in the Archaeometry Laboratory at MURR

were expressed in ppm. For this reason, they were renormalized

in order to make the results comparable with those obtained byTXRF. Thus, using the equation

%vs Fex 100cx

cFe2

for the same group of elements it was possible to transform

quantitative data cx (ppm) into semi-quantitative results

expressed as % vs Fe.

Fig. 3 shows the TXRF results obtained for Set-1, Set-2 and

Set-3 compared with INAA measurements, all expressed as

relative concentrations in % vs Fe.

The results obtained in Fig. 3 show that different behaviors

were present for the elements evaluated. Enrichments of the

elements As, Al, Rb, Sr and K; impoverishments of the

elements Mn and Ti; U-up behavior for the element Ba; and

finally, U-down behavior for the elements Cr, Hf, Ni, Zn, Ca, V,

Cu, Ga and Y, with respect to the particle size fraction analyzed

were found. In the case of the enrichments, the fraction of larger

particle sizes (Set-3, between 0.1 and 10 m), was higher for

these elements. In the case of the impoverishments, the fraction

of lower particle sizes (Set-1, between 0.01 and 2 m) washigher for these elements. In the case of U-up behavior, the

fraction of medium particle sizes (Set-2, between 0.05 and

5 m) was the lowest for this element. In the case of U-down

behavior, the fraction of medium particle sizes (Set-2, between

0.05 and 5 m) was higher for these elements.

The behaviors observed experimentally can be explained

considering the heterogeneous nature of the clay. Clays are

multi-layered mineral mixtures in which there are differences in

mineral and chemical composition between particles of different

sizes. This fact implies that the densities of micro particles can

be different. This finding contradicted the first main require-

ment of our approach by lost of chemical homogeneity.Therefore, from the quantitative point of view the method of

sedimentation can be rejected to analyze this kind of material by

TXRF. On the other hand, the procedure developed could open

the way to evaluate the chemical composition of a generic solid,

based on its size and it could have interest in environmental

pollution studies (e.g., chemical analysis of polluted soils or

urban aerosols to diagnose air pollution from traffic and

factories).

Three elements, not analyzed by INAA in this material, Cu,

Ga and Y, have been determined by means of TXRF. From the

archaeological point of view, this fact is of great relevance since

an increase of the number of analyzable elements in an

archaeological material implies an increase of the number of

variables able to solve its geographical origin.

2.3. Procedure of solid chemical homogenization

In order to resolve the phenomenon of segregation produced

by the procedure of sedimentation and to comply with the first

Fig. 2. Representative TXRF spectrum from Ohio Red Clay-2 reference sample.

Fig. 3. Relative mass fraction for the 19 elements analyzed by TXRF for the

three different particle size fractions (Set-1, Set-2, Set-3) compared with INAA

results. Error bars obtained with n =5 for TXRF and n =20 for INAA.

1125R. Fernndez-Ruiz, M. Garca-Heras / Spectrochimica Acta Part B 62 (2007) 11231129


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main requirement, it was decided to prepare a new set (Set-CH)

in which the sedimentation problems were diminished.

2.3.1. Sample preparation

First, the sample was ground by an agate mortar until it had aparticle size lower than 30 m. Then it was ground again for 1 h

by using a vibration micro-pulverizer equipped with a ball and

base of agate. Afterwards, 1 ml of high-purity water was added.

Next, the mix was poured into a test-tube in which high-purity

water was added up to 10 ml. The sample was homogenized for

1/2 h by ultrasonic disaggregation in order to disperse possible

agglomeration of particles. Finally, the particle size distribution

in suspension was checked by using QELS until it had the

required distribution and, therefore, was in accordance with the

second main requirement. When the sample had this size

distribution, it was again homogenized and, maintaining the

agitation always constant, 5 l of the suspension was placed on

the quartz flat carrier and dried on a ceramic hot plate. All

manipulations were made in an A-100 class laminar flow

chamber.

2.3.2. SEM verification

In order to verify the third main requirement, different kinds

of depositions were generated on quartz sample supports and

observed by SEM after gold metallization. The first one was a

suspension in water, showing a distribution of concentric ringsin shape, probably associated with an edge effect in the liquid

solid interface during the water evaporation process (Fig. 4-a,

b). In order to obtain a distribution of particles that were isolated

and homogeneous, we experimented with different agents of

different surface tensions, particularly with toluene and high-

purity water. It was established that toluene provided the best

distribution (Fig. 4-c, d). Nevertheless, it was noticed that this

agent seriously distorted the analytical determinations. Probably

the observed quantitative analytical distortion can be attributed

to the mountain effect, at micro particle level, that can be

appreciated in Fig. 4-d. This effect produces the lost of the thin

film geometry and the appearance of the energy dependent

matrix effect, which is in agreement with the experimental

observations. As a result, we finally decided to use high-purity

water, even though such a water did not strictly comply with the

Fig. 4. SEM micrographs of depositions according to different sample suspension agents. ab: Ohio Red Clay-2 in high-purity water. cd: Ohio Red Clay-2 in toluene.

ef: Archaeological pottery sample in high-purity water.



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third main requirement for clays. In practice, water offered the

best analytical results.

The final objective of this study was the application to

ceramic materials. Due to this fact, we tested the behavior of a

pottery sample using water as suspension agent. Fig. 4-e and f

shows the aspect of an archaeological pottery preparation

suspended in water, where a homogeneous distribution of the

deposition can be observed.


Semi-quantitative results were obtained by replicating 5

analyses of the same Ohio Red Clay-2 reference material.

Table 1 shows the results of the 18 elements chosen for routine

analysis in Set-CH. Data were acquired the same way as that for

Set-1, Set-2 and Set-3.

Results show that, in this case, the accuracy for Cr, Hf, Rb,

Ni, Al, Ba, Ca, K, Mn, Ti, Fe and V with respect to INAA valueswas excellent, as is shown in Table 1. The accuracy was

evaluated by measuring the recovery percentage with respect to

the INAA values. For the previous 12 elements the recoveries

vary from 91% for Hf to 110% for V. The precisions obtained in

the measurements by TXRF were evaluated by measuring the

coefficients of variation (CV) expressed as percentages. TXRF

CVs vary from 0.8% for Ti to 27% for Hf, whereas in the

analysis by INAA CVs vary from 2% for Mn to 106% for Sr.

These analytical aspects do not imply that TXRF is a more

powerful tool than INAA, but that TXRF may offer both

precision and accuracy comparable with and, in some cases,

better than INAA.

It is important to note the disagreement between the INAA

and TXRF values for the elements As, Sr and Zn. For these

elements, TXRF presents a high sensitivity and they are

unequivocally detected as the spectrum associated with the

reference material shown (Fig. 1). Previous results (Fig. 3)

present the same systematic increase in the relative concentra-

tions of As, Sr and Zn with respect to INAAvalues. This implies

that the systematic increase is independent of the averageparticle size fraction analyzed. One possible explanation can be

attributed to high variations in the sizes of mineral phases

present in the clays and associated to As, Zn and Sr as Prange et

al. suggest [15].

A deeper study of this discrepancy was carried out in order to

understand the differences found. By means of the TXRF 8030c

spectrometer, a sample-angle scan of one representative sample

of the Set-QH was carried out. The scan was performed from

0.25 to 2.25 mrad, around the critical angle for quartz, with a

step of 0.1 mrad and a measurement time per step of 100 s. Fig.

5 shows the angular behavior of the following elements: Fe, Ti,

Rb, K, As, Sr and Zn. The different curves were normalized atthe critical angle for quartz, defined as the inflection point of the

angular curve, located at around 1.87 mrad.

The angular behavior for the representative elements that

present good accuracy (Fe, Ti, Rb and K) is very similar (see

Fig. 5) and is in agreement with the analytical results (see

Table 1). In contrast, the angular behavior for the inaccurate

elements (As, Sr and Zn) presents strong differences with

respect to the Fe behavior chosen as reference. The angular

behavior of the elements As, Sr and Zn presents strong

oscillations in its signals. These oscillations are typical when the

particle sizes are lower than 100 nm [15] and they are usually

associated to the appearance of X-ray interference effects in the

interference region of TXRF. In this case, the solid particles

associated to As, Sr and Zn should be in the range between 20

and 50 nm to explain the observed modulation of their angular

dependence.

2.4. Application to an archaeological case-study

From an analytical point of view, the primary objective of

this study was to assess the compositional variability of the

Table 1

Ohio Red Clay-2 elemental relative mass fraction expressed as % vs Fe for

INAA and TXRF

Element INAA (n =20) CV (%) TXRF (n =5) CV (%) Accuracy

% vs Fe % vs Fe Recovery(%)

As 0.028 0.002 7.2 0.040 0.002 4.3 146

Cr 0.18 0.01 5.6 0.180 0.010 5.8 101

Hf 0.015 0.001 6.9 0.013 0.004 27.0 91

Ni 0.14 0.03 21.4 0.150 0.009 5.8 107

Rb 0.36 0.02 5.6 0.354 0.004 1.0 98

Sr 0.05 0.06 106.0 0.131 0.004 2.8 249

Zn 0.18 0.02 11.1 0.284 0.009 3.2 157

Al 185 6 3.2 171 4 2.4 92

Ba 1.1 0.3 26.3 1.24 0.06 4.5 109

Ca 3.0 0.4 13.3 2.81 0.04 1.4 93

K 64 16 25.1 69.3 0.8 1.1 109

Mn 0.51 0.01 2.0 0.50 0.01 1.9 98

Ti 12.0 0.6 5.0 12.35 0.10 0.8 103V 0.39 0.01 2.6 0.43 0.01 2.3 110

Cu n.m a n.m n.m 0.040 0.005 12.7 n.eb

Ga n.m n.m n.m 0.050 0.002 3.6 n.e

Y n.m n.m n.m 0.08 0.01 12.5 n.e

Fe 100 reference 100 reference

a Not measured.b Not evaluated.

Fig. 5. Sample angle scans versus integrated areas for Fe, Ti, Rb, K (circles) and

Sr, Zn and As (triangles). Continuous lines are B-Spline interpolation.



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pottery ensemble provided by some archaeological excavations,

as a possible indicator of different sources or production units.

In this archaeological case, a study carried out by TXRF on

ceramic materials from the Celtiberian archaeological site of El

Palomar (Aragoncillo, Guadalajara, Spain) is briefly illustrated.

The settlement is located in the Upper Jaln Valley, adjacent tothe Upper Duero Valley in the north-eastern part of the Spanish

Central Meseta. A total of 24 representative samples from the

different percentages of each fabric or type of ceramic

manufacture present in the settlement were analyzed (EP-1 to

EP-4 Fabric 1; EP-5 to EP-8 and EP-13 to EP-21 Fabric 2; EP-

22 to EP-24 Fabric 3; EP-9 to EP-12 Fabric 4). Analyses were

carried out by TXRF according to the solid chemical

homogenization procedure mentioned above for Set-QH. Two

statistical procedures were used in the exploration of data:

cluster analysis and principal components analysis. Both were

carried out on log-transformed data on the concentrations of 18

elements determined, excluding Fe, in order to balance the

difference of magnitude between the major and trace elements

[16]. We also introduced the values of the standard in the

statistical analysis, either those obtained by INAA or by TXRF

(Set-QH). We used such values in order to check the capability

of TXRF to discriminate groups of different composition.


The cluster analysis employed the average linkage of themean Euclidean distances matrix. The resulting dendrogram

suggests that the data set had two parts, one of them constituted

by standard measurements, and the other constituted by the 24

samples analyzed. Within the latter, it may be observed that

samples are separated into two sub-groups. There are sherds

from Fabrics 2, 3 and 4 in both sub-groups, whereas only in the

first one sherds appear to belong to Fabric 1. Further clarity was

introduced as a result of the use of principal components

analysis. The three first components summarized 71.89% of the

total variation in the data. In Fig. 6a, the plot represents sample

scores with respect to the two first components. Three distinct

groups can be observed. All samples belonging to Fabric 1appear on the left. The rest of the fabrics appear at the center.

The two standards plot on the upper part of the diagram.

Correlations between the variables responsible for these

associations may be seen in Fig. 6 b. The first component

summarized 45.29% of the total variation. Four elements were

positively correlated with this one: Ba, V, Hf and Mn, whereas

Al, Ti, Rb and Cr had a negative correlation. The second

component summarized 18.48% of the total variation. Cu, Ni,

Rb and Cr had a positive correlation and Zn, Sr, K and Ga had a

negative correlation. Finally, the third component (not repre-

sented in the figures) had Y, Ni, Cr and Cu correlated in a

positive way, whereas Ca, As and K had a negative correlation.

Therefore, the discrimination of fabric 1 was related to the first

component (Fig. 6a).

To summarize, the statistical analysis showed two distinct

associations. One group was constituted by fabric 1, and one

group was formed by the remainder of the fabrics. The

compositional variability observed seems to reflect a high

homogeneity in the sherds analyzed, which might indicate a

local provenance. The presence of two associations in the data

set may be related either to the exploitation of two different

sources of raw materials or to the presence of different

production units. The percentages of fabric 1 in the total pottery

ensemble, as well as typological forms associated to this fabric,

do not suggest a foreign origin for this type of manufacture.Therefore, the local character of these productions is suggested

in a preliminary way. This indicates that this pottery could have

been manufactured in the geographical area where El Palomar is

located. However, it is not possible to establish that pottery was

elaborated in the archaeological site itself, particularly in view

of the absence of remains related to pottery production. Finally,

it is evident that the inclusion of analytical data for the standard

Ohio Red Clay-2 (ST-1, INAA results and ST-2, TXRF results)

has revealed the ability of the TXRF technique to detect

compositionally different groups.

3. Conclusions

The method of sedimentation can be rejected to analyze this

kind of material by TXRF for archaeological applications.

Fig. 6. (a) Plot of the first two principalcomponents scores derived from analysis

of the 24 pottery EP samples plus results of the 2 standards. ST-1 INAA results

and ST-2 TXRF results for Set-QH. (b) Weight of the 17 variables taken into

account.



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However, the TXRF procedure developed could be a fruitful

avenue to evaluate the chemical composition speciation of a

generic solid, based on its size and it could have interest in

environmental pollution studies.

A reliable sample preparation process is needed forapplication of TXRF to the analysis of archaeological ceramic

materials and the chemical homogenization approach complies

with this requisite. This procedure implies that the ceramic

sample has chemical homogeneity, average particle size around

1 m and lower than 10 m, and a chemically homogeneous

distribution of its particles. The final procedure can be

summarized as follows: homogenization of the samples by a

high grinding process, suspension of the fine-ground mixture of

the whole sample in high-purity water, ultrasonic disaggrega-

tion of such suspension, and deposition with continuous

agitation of an aliquot of that suspension on a flat carrier. The

more important aspects are the following: the chemicalhomogenization procedure has proved to be quick, relatively

easy, and inexpensive and, in addition, does not require any

chemical manipulation.

The analysis was performed for 18 elements: Al, Ca, K, Ti,

Fe (majors); Mn, Zn, Sr, Rb, Cr (minors) and As, Hf, Ni, Ba, V,

Cu, Ga and Y (traces). The results obtained show a high

accuracy for Cr, Hf, Rb, Ni, Al, Ba, Ca, K, Mn, Ti, Fe and V.

The recoveries (accuracy) obtained vary from 91% for Hf to

110% for V. The precisions obtained vary from 0.8% for Ti to

27% for Hf, whereas in the analysis by INAA they vary from

2% for Al to 106% for Sr.

TXRF results for the elements As, Sr and Zn presented an

unexpected inaccuracy with respect to INAA values. These

unexpected values were studied more deeply by means of angle-

scan measurements and an anomalous behavior was found.

Such behavior has been associated to the presence of particle

sizes between 20 and 50 nm corresponding to mineral phases

associated to As, Sr and Zn and therefore, the associated

interference effects explain and justify the differences observed

between TXRF and INAA values.

The archaeological case-study shows that TXRF is a useful

technique for the determination of the compositional attributes

of ceramics. The comparison of these results with data

previously obtained from the clay reference material clearly

shows the ability of the technique to distinguish groups ofdifferent compositional nature. On the other hand, TXRF has

provided analytical values comparable to those provided by

INAA for 15 elements. Three additional elements (Cu, Ga and

Y) present in the Ohio Red Clay-2 standard were determined by

TXRF, even though they were not analyzed by INAA.

At the current stage of our research, TXRF provides semi-

quantitative results. This fact is not a serious drawback for

archaeological applications as the archaeological case-study

demonstrates. In any case, we are currently working in the

development of new TXRF strategies which will be certainly able

to quantitatively analyze this kind of materials in the next future.

Acknowledgements

The authors wish to express their gratitude to Dr. Hector Neff

and Dr. Michael D. Glascock (Archaeometry Laboratory at the

Missouri University Research Reactor Center) for giving thempermission to use a Ohio Red Clay-2 standard as well as data of

their measurements by neutron activation.

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Fernandez Ruiz y Garcia Heras - Estudio cerámico por Flourescencia