Gamma-Rayinduced thermoluminiscenceo! majolica pottery as an indicator

of its provenience1. E. VAZ, and Y. M. CRUXENT

The thermoluminescentemissioninducedby gamma-rayirradiationin samplesof majolica pottery was analyzed Lo determineif theirartificially-induced thermolurninescence(TL) could be used as anindicator of provenience.It has beenrecognizedfor some time thatan independentmethod of determining the provenienceof potterywould be of significant value to the archaeologist.Two analyticalmethodsare currently in use for the determinationof provenienceinpottery: neutronactivation analysisusing gamma-rayspectrometry’,and optical spectroscopy2 Sorne work has also beencarried out inthe utilization of Móssbauerspectroscopy~~ in provenienceproblems.Thesemethodsare basedon the fact that the chemical compositionof clays used in the manufactureof pottery dependson the sourcerocks, and in the geochemicalconditions that producedthe sediment.Thesetwo factors will give rise to clayswith enoughvariation in theirminor, and trace-elementcontent to allow distinetion between thesourcesof the raw materialsused in the preparationof the paste.

The TL measurernentspresentedhere were carried out in the claymatrix of majolica pottery manufacturedin pottery centersin Europe,and Mexico. This type of pottery is a porous pottery of soft pastewith ahard covering of opaque,vitreousmaterial, It was wheel-rnadein Europefrom the XV to the XVII century,and in severalplacesin

¡ 1. PERLMAN, E’. ÁsARo, Archaeometry11,21 (1969).2 J-~~ ~ CATLING, Arcbaeometry6> 1 (1963).3 D. R. Cousiws,K. G. DIIARMAWMUWNA, Nature223> 732 (1969).4 It H. 3. GANGAS, A. Kosnns,A. SrMoPouLos, 3. VOcOTOPOULOJJ, Nature 229,

485 (1971).

50 1. E. Vaz y 1. M. Cruxent

the New World after the Conquest.The origin of the samples,andotherpertinentdata arepresentedin Table 1.

The clay matrix of the sherds was ground and sieved, and the74-177 xm fraction was usedfor the TL measurements.Portionsof thesampleswere irradiation with gammarays from a Cesium-137sourceuntil their TL output reachedsaturation.After irradiation with 2 x t06Roentgensof gammaradiation, the sampleswere kept in the dark atroom temperaturePor 48 hours to allow the low-curvepeakto stabilize,The gamme-rayinduced TL of 18 mg aliquots of the material wasmeasuredin a nitrogen atrnosphercwith a TL analyzer.The sampleswere heatedlinearly from room temperatureto 500~ C at 10~ C s -

The reproducibilityof themeasurementsis within ±5 %.

Figure 1 shows a set of glow curves obtainedfrom samplesfromeachof thepottery manufacturingcentersstudied.Glow-curve measur-ements of each of the samplesthat were analyzedare presentedinTable 1 where the glow-curve peak temperatures,the peak-intensityratios, andthe areaunder the glow curve areshown.

In thepreparationof the pasteusecl in the manufactureof pottery,the clay is mixed with temperingin the forrn of impure sand.Both oftheseconstituentsof the pastewill emit TL when the clay matrix ofthe sherdis heatedafter being irradiatedwith nuclearradiation.Thisproperty of the material has been used to date ancient potterybecausethe mineralsPound in the clay matrix canaccumulatesorneofthe energy released by the radioactive decay of U, Th, and K-40impurities presentin their crystal lattices. In addition, the TL outputof any one of ihe mineral constituentsof the pastedependson theconcentrationof traceelementswithin the erystalthatact as activator,or luminescentcenters.It is, therefore,reasonableto assumethat theshapeof the glow curve obtainedafter irradiation of the elay matrixwith gammarays dependson the type of clay, andon the temperingusedto makethepot, as well as on the concentrationof traceelementsin thesetwo constituentsof the paste.

IP theseassumptionsarecorrect>it should bepossibleto usegamma-ray inducedTL to distinguish or relate pottery sherds Pound ir anarchacologicalcontext. By irradiating the clay matrix with gammarays until its TL output is saturated,one is assuredthat eachof thethermoluminescentmineral fractionsin the pasteis contributing fullyto the total TL output. Analysesof the naturalTL output of the claymatrix would not have beensuitable to this study becausethe lowlevels of naturalTE measuredin the samplesdependon the raclloactive-impurity content of the specimen, its age, and the environmentalconditionsunder which it was preserved.

M. 3. AITKEN 1). W. Z[MMHRMAN, S. 3, FLEMINO Nature 219, 442 (1968),

Gamma-Rayinduced ther,nolu,niniscenceof rnajolica potcery... 51

lO>— - — Geado, so-np/e MG

GesM’/o, súmple Nt’ 79

8- Teruel, somple /Vt’ 235

6

4

SE

‘E

5— - — Gota/ato,sorople Nt’83— Puebla (x/Q>, sao~p/eÑ~ 24/

4 A/biso/o, soniple N9 /2

3 1

300 400 500

Tempero/ura (OC)

FIGURA L—Rep>-esentativegamma-ray inducedTL glow curves of each ofMe pottery ;nanufacturing centerssiudied.

52 1, E. Vaz y 1. M. Cruxent

Ihe results of the TE measurementspresentedin Figure 1, audin Table 1 show that the assumptionsdiscussedearlier are reasonablyvalid. It is evident from the datapresentedin Table 1 that the glow-curve measurementsare similar, within relatively narrow limits, inthe samples of majolica pottery from the same locality. However,these measurementsare substantially different in the sametype ofpottery manufacturedin diferent localities. Ihesedifferencesaremoreclearly seenin the curves shownin Figure 1.

Among the samplesfrorn any one of the six different localitiesstudied, the largestvariation in the TL measurementsis found in themeasurernentof the areaunder ihe glow curve. This variationappearsto be due mainly to changesin the transpareneyof the material pro-duced by the baking of the pottery. It should also be pointed outthat although the samplesfrom Teruel, Spain> range in age from theXV century to the XVIII century, the TL spectraare very similarfrom sampleto sample.This similarity indicatesthat ihe sourceof theraw materials used in the preparation of the paste was the samethroughout the ycars. It is probable that the samecommnentcan bemadeabout the samplesfrorn the other localities studied,but we donot know with certaintytheapproximatedateof manufactureof rnostof thesesamples.

Theresultsobtainedto dateindicatethat the gamma-rayinducedTLof majolicapottery is specific to the locality wherethe artifactsweremade. It is posaiblein principIe to apply the TE techniquedescribedhere to classify according to origin other types of pottery Pound inarchacologicalsites. This would require a systernaticstudy of thecharacteristieTE spectraof the principal types of pottery. It is hopedthat analysessimilar to the ono presentedhere could be used tocornplementtypological studies6 of majolica pottery found archacolo-gicallíl in the Americas.

Instituto Venezolanode InvestigacionesCientilicas. Ca,raCas.

6 3 M, GOGOIN, SpanishMajolica in the New World (Yale University Publi-cations in Anthropology,No. 72, 1968).

Wc thank V. Betancourtbr technical assistance,and G. Bemsky for aditingthe manuscript.

Gamma-Rayinducedthermoluminiscenceof inajolica pottery... 53

Tabla ‘ - TLmoasLrnr,rrtn ‘O LLtLJLI¡Ca palían.

Contar y POJO PraL ‘“LOr,s’tyLrmrerataro (Le) raL¡ 0

lOca llt¡L

O pat

0’VtV

xt

¡¡0—00

alO-alt

0’ ‘‘—x¡y

Ol’ ‘—Clv

00

XI’ ‘-.010

¡‘O-aa

OIL’ ¡

xv’’’

a¡a,, ¡

xv’

O ‘‘‘O’ O

xv

xv’’

25,180.300

‘25, ‘80,300

135• 185. 3 00

xv’’

60’’

Cast~’’a. S»r’r

125. 190,2’í5

160,275

al 1.6, bí 2,3

al 1.4, 80 2.4

al ‘.2. tI 2,2

al II, tI ¡.1

a) ‘.4. 8) ‘.7

al 1.1, tI 1.0

a) ‘.6, LI 2

al 1.2, tI 2.14

al ¡.2, 0) 3.’

al I.lí, tI 2.3

al ‘.6, lv> 2.0

al 1.6, 81 2.3

al 1.4, 8) 2.0

a) ‘4í, tI 2.14

III 0,9, 8) 2

al ‘.7. LI 2.6

a) 1.’, LI 2

El 04. 8) 0.8

al 0.5, 81 1

0) 0.7, tI 1

al 2.7, 8) 0.9

a) 0.7. tI 0.9

a) 0.8, 83 0.9

a) 0,’). 8) ‘.1

al 1.6, b> 1.8

0> 3.0, 8) 1.8

a) 2.5 8) ‘.5

nl 1.5. 8> 1.7

a) 2 , 8) ‘.9

o) 0.1

a) 0.6

(‘ala—ca rvearra Ircí

8.8

6.3

7.1

19

6.5

9

5.2

6.2

9.6

3.5

10.6

12.9

6.2

6.3

7.3

“.3

3.9

2.2

6

12

12

10.6

S.l

4.6

10.6

9.3

Tarar’.

Sanrín

IB

‘9

20

27

28

3’

35

36

37

38

39

10~

42

43

56

239

lo

12

‘3

48

5’,

33

3’,

83

89

29

30

sp,’,,

A’blsola. ‘LO’y

1. E. Vaz y 1. M. Cruxent

Ta8’ e 1. lI. n,eaXurrnlenLv Ir v.aJol ‘Ca polio ry (Cori .1

Cortan. IrakLeaperaturc Uf)

160, 275

Gorda, ljollar.d XVI ‘~XVIIl 135,l8O.300

XVIII

160.285

54

Savp lo Local iv

(astI II,, ipal”‘.5

“7

55

77

78

79

80

82

214

57

58

65

66

68

70

53

60

241

21a0

237

239

242

Peal. 1 nitos ‘iv‘rilo

o) 0.6

a) 0.6

a) 0.5

a) 0.9

a) 0.5

a) 0.6

a) 0.9

al 0.7

a) 1.1, 81 1.1

a) II, 81 1.1

,l 344, 8) 1.3

a) 1,2, 81 1.2

a) .14. 81 1.2

a) .3, 81 1.2

a) 0,9, 81 1

a) 0.3

al 0.14

a) 0.6

al 0.14

rl 0.3

al 0.2

al 0.2

SI 0w-Curvearr, nf)

II.’)

9.7

9,8

10.5

7.4

10.14

5.8

14.9

7.3

16

8.6

13.2

314.6

10.5

9.5

0.6

0.6

8.4

0.7

0.8

0.6

Pueblo, >lea’lco

• a) RaLlo o’ tIno ‘‘o8 ienperniurc glow peak lo tilo eNdIe io,flpolatrré ~Iow poak

81 RaLlo or tho <‘lidIe terperainro glow paulo Lo tIlo oua Lampora turs 0mw peak