Auchaeoinetry 2 4 , 2 (1982) 191-198. Printed in Great Britain
TECHNOLOGICAL EXAMINATION O F
LOW-FIRED TERRACOTTA S T A T U E S FROM A Y I A I R I N I , KEA
Y. MANIATIS, A. K A T S A N O S
Dept. of Physics, N.R.C. Demokritos, Aghia Paraskevi, Attiki, Greece
and M . E . CASKEY
Dept. of Classics, University of Cincinnati, Ohio, U.S.A.
INTRODUCTION
The island of Kea (ancient Keos), one of the western Cyclades, lies off the coast of Attica
opposite Makronisos and Lavrion. Its greatest natural asset is the enormous harbour at the
northwest end, a protection for shipping that has afforded the island unique opportunities from
very early times and was, no doubt, behind the choice of the little peninsula of Ayia Irini
within the harbour as a site for settlement in the Early Bronze Age.
Excavations began at Ayia Irini in 1960, continued in 1961, and from 1963 to 1968, with
supplementary tests and soundings in the years 1969 to 1976. The work is under the direction
of John L. Caskey* for the University of Cincinnati, under the aegis of the American School of
Classical Studies. Results have surpassed expectations with the finding of a settlement that
persisted from EB I1 well down to LH I11 times.
Of great interest is the discovery of a sanctuary, built initially in the Middle Bronze Age, that
continued as a place of worship at least into Hellenistic times. Among the finds from the building
are large terracotta statues made of local clay. They represented dancing or standing female
votaries; they stood in the sanctuary and may have been intended to show a perpetual liturgy in
connection with the epiphany of a divinity. How many there were, we cannot say; their fragmentary condition precludes an accurate estimate of their original numbers, but it is safe to say that
there were more than fifty-five. They range in size from 60 or 70 cm to a full life-size (Caskey 1982).
Fragments of the statues were recovered from all over the temple, from depths of around
60cm below present sea-level up to very near the surface of today. They lay in the debris of
the fallen building with pottery datable to LM IB/LH I1 and in accumulations of later times.
Some fragments were built into walls and benches of later phases of the temple. But the place
of finding is not the determining factor in the condition of the various pieces. The soil in
which they lay was much the same throughout, and all were subject throughout the centuries
of their burial to the inroads of the salty sea. With the exception of a few pieces, observable
differences in quality and in the state of preservation seems attributable rather to initial firing
than to anything else.
The statues were made of very coarse clay. They were fired generally in an oxidising atmosphere, but the firing was not always consistent throughout. The making of such statues was no
small achievement. Clearly a knowledge of the firing characteristics of coarse clays and the
working of kilns necessary for a successful firing of large statues was well in hand at least by
the opening years of the Late Bronze Age.
*Prof John L. Caskey died in November 1981.
191
192
Y. Maniatis, A . Katsanos and M. E. Caskey
The statues have been divided into groups based on a coincidence of the technique of
building, the fabric, and the formal characteristics of the figures. Nine, or more, distinctly
different types suggest that there were at least as many separate workshops or minor establishments of some kind.
To what extent the significance of the groups is chronological is uncertain. Clear evidence
from the excavation has provided a terminits anfe quem of ca. 1450 B.C. (LM IB/LH 11) for all
but the large fragmentary statue that we have catalogued as Group 15. This one figure was
made in LH 111 times, probably in LH IIIA2.
Fragments representative of seven main groups and one subsidiary group (3/4) were examined
scientifically in t h s work in order to obtain information about the firing conditions applied in
their manufacture.
SCIENTIFIC T E C H N I Q U E S
Scanning electron microscopy (Cambridge-1 50) was used t o study the microstructures of the
terracotta samples and infra-red spectroscopy (Perkin Elmer-257, Grating Spectrometer) for
observing certain mineral alterations. In addition proton induced X-ray emission (PIXE)
elemental analysis (Katsanos et al. 1976, Katsanos et al. 1978) was applied for the composition
of the samples. This was done with the Tandem van de Graaff accelerator of the N.R.C.
Demokritos.
The examination of fresh-fractured surfaces of ceramic samples under the scanning electron
microscope (SEM) provides information on the internal morphology of the clays developed
during firing and the degree of Vitrification (Maniatis and Tite 1978, Maniatis and Tite 1981).
This information combined with known morphologies of clays and pottery or by refiring
samples from the terracottas in the laboratory and reexamination with the SEM lead to the
determination of the firing temperatures used in antiquity. In addition the degree of vitrification
(or amount of glass) present in the microstructure of a fired clay body gives information about
its strength, hardness and porosity which are associated with the use of the object and its state
of preservation.
Furthermore the information obtained with the proton induced X-ray emission analysis
(PIXE) apart from helping to distinguish between groups of composition, provides data on the
type of clay used, i.e. calcareous or noncalcareous and low or h g h refractory. These properties
which affect the internal morphology developed during firing (Maniatis and Tite 1978) are
needed for a more accurate estimate of the firing temperature without repeated refirings in the
laboratory.
The infrared spectra provide information on the precense or not of hydroxyl water in the
clay mineral lattice (Grim 1968, Fanner 1979) and can therefore verify whether dehydroxylation or not has been accomplished. This if combined with the SEM results assists the assignment of low firing temperature ranges below the onset of vitrification.
R E S U L T S A N D DISCUSSION
The PIXE analysis showed (table I ) that the average compositions of all the groups are about
the same. Especially when one considers the coaneness and inhomogeneity of the samples,
as well as the experimental errors, the mean compositions agree well with local Kea clays.
Some differentiation is observed in Ni, Zn and Rb but not so significant to suggest a totally
different origin.
Sample
K
Ca
Ti
V
Mn
Fe
Ni
Zn
Rb
Sr
Zr
@m)
% weight
Group-I
TC5
TC11
TC14
TC18
TC19
2.6
3.3
2.6
3.4
3.3
0.99
0.49
054
0.40
0.36
0.30
1.36
0.40
0.31
0.29
0.018
0.040
0.022
0.021
0.017
0.06
0.06
0.38
0.08
0.09
7.0
7.6
9.0
8.1
7.9
89
118
103
148
141
58
122
101
118
84
53
56
56
53
49
108
41
70
31
32
38
93
45
77
54
Group 3 , 4 , 3 / 4
TC4
TC7
TC12
TC17
TC15
3.7
3.3
2.6
3.4
3.4
0.47
055
1.1
0.41
0.45
0.32
0.37
0.30
0.29
0.31
0.026
0.026
0.019
0.021
0.020
0.13
0.12
0.08
0.14
0.22
75
6.9
7.1
7.9
7.4
68
70
81
101
94
39
95
61
46
60
72
75
54
70
65
29
44
56
42
64
96
118
66
64
Group-5
TC13
3.4
053
0.36
0.021
0.16
7.2
79
50
67
56
74
Group-6
TC6
2.9
1.70
0.33
0.026
0.10
7.9
98
43
59
119
57
Group-8
TC1
TC3
TC8
TC9
TClO
TC16
3.7
3.4
3.2
3.2
3.2
3.4
0.91
0.60
0.40
0.59
0.68
051
0.34
0.37
0.30
0.31
0.37
0.44
0.030
0.024
0.022
0.024
0.023
0.023
0.11
0.11
0.11
0.14
0.10
0.14
6.9
7.1
6.5
7.2
6.8
7.4
62
60
71
53
64
87
52
42
41
47
82
41
61
79
71
61
70
66
101
65
37
64
70
60
69
75
55
102
118
65
Group-15
TCla
TC2a
3.0
3.3
1.40
153
0.40
0.35
0.017
-
0.06
0.21
6.5
7.7
94
112
106
151
57
70
57
-
76
The amounts of K, Ca, Ti, Mn, and Fe which are associated with the fluxes in a clay body
suggest that the clay is generally of a non-calcareous, low-refractory type (Maniatis and Tite
1978). Low refractory in fact means that vitrification begins at low temperatures.
The scanning electron microscopy of the terracotta sherds showed that the microstructures
generally fall into two categories. These which have just developed some vitrification in the
form of very fine threads of glass in various places inside the clay body (figure 1 and 2) and
those which are completely unvitrified (figure 3 or 4). In low-refractory clays the commencement of vitrification (or initial vitrification stage: IV) is reached at 750-800°C in a reducing
atmosphere and at 800-850°C in an oxidising atmosphere (Maniatis and Tite 1981). Given
that the IV stage is not fully and uniformly developed throughout the clay body and that the
atmosphere, judging from the colour of the sherds, is generally a mixture of reducing-oxidising,
the slightly lower temperature range (i.e. 750-800°C) has been assigned for all the sherds
exhibiting initial vitrification.
In the case of the completely unvitrified sherds the SEM cannot define firing temperature
ranges except to specify the upper limit, i.e. 750"C, since this is the lower temperature where
Y. Maniatis, A. Katsanos and M. E. Caskey
194
Figure 1
Figure 2
Sample TCIl (group 1 ), initial vitrification ( I V ) , long threads ofgkss apparent.
Sample TC13 (group S), IV stage. Threads or filements of glass can be seen around the central
part of photograph.
Technological Examination of Low-fired Terracotta Statues from Ayia Irini, Kea
Figure 3
Sample TC3 (group 8 ) , no vitrification, flaky structure.
Figure 4
Sample TC8 (group 81, no vitrification, flaky structure.
195
196
Y. Maniatis, A . Katsanos and M. E. Caskey
vitrification can possibly appear. The difficulty of the SEM for more precise firing temperatures
for the non-vitrified samples lies in the fact that the microstructure does not change at temperatures lower than 750°C in any obvious way detectable with the SEM. However in those
with a lower than 750°C firing temperature mineralogical changes are known t o be taking
place and particularly dehydroxylation. This is the process during which the clay minerals
loose the crystalline hydroxyl (OH) water and begin to disorganise. In general dehydroxylation
takes place between 400-600°C but for some minerals it can continue up t o 800°C or so
(Grim 1968). In an attempt to determine a lower limit for the firing temperatures of the nonvitrified sherds we used infrared spectroscopy for the detection or not of hydroxyl water
present in the clay lattice. All sherds were found t o contain a fair amount of absorbed water
but in only 4 out of the 20 samples was the presence of hydroxyl crystalline water verified.
This water absorbs infrared radiation between 3500-3600 wavenumbers (cm-') and also at
around 900cm-' if coordinated with Fe3+ (Grim 1968, Farmer 1979). Figure 5 shows two
infrared spectra. TC17 is typical of samples containing OH water showing absorption at around
360Ocm-' and also at just above 900cm-' which indicates the presence of iron hydroxyl
groups still in the clay body. TC14 is typical of the rest not showing these hydroxyl absorptions.
We assume therefore that the dehydroxylation in the samples with spectra like TC17 is incomplete and therefore the firing temperatures should be generally below about 650°C. 'Below', in
this case obviously means any temperature between around 650°C and completely unfired
sherds.
Figure 5 lnfrared spectra of two typical srmples. TCI 7 exhibiting OH-absorptions at around 3600 cm- '
and 900 crn-'. TC14 dehydroxylation completed.
On the other hand the group which exhibits complete dehydroxylation (i.e. like TC14) can
be divided into two groups based on the SEM results. one with no-vitrification and the other
with initial vitrification. The latter group's firing temperature is determined solely by the
SEM. however in the case of the non-vitrified samples one finds infrared spectra very useful
because they indicate a temperature above the hydroxylation range i.e. above about 650°C
and this combined with the SEM's upper limit of 750°C gives a firing temperature range for
this group of 650-750°C.
An argument against the presence of OH absorptions in the infrared spectra as being
Technological Examination of Low-fired Terracotta Statues from Ayia Irini, Kea
197
indicative of incomplete dehydroxylation could be that these sherds may have been rehydroxylised after initial dehydroxylation (i.e. reabsorb OH and recrystallise) during the millenia of
burial in the ground. This possibility can not of course be entirely excluded but given that all
samples were buried under the same conditions the presence of OH in some of them either
original or reabsorbed indicates a lower firing temperature anyway.
With the combination therefore of the above techniques firing temperatures have been
assigned as follows: (1) sherds exhibiting initial vitrification: 750-800°C (2) sherds non-vitrified
but completely dehydroxylised: 650-750°C and finally (3) sherds non-vitrified and not
dehydroxylized: below 650°C. Table 2 shows the combined results from the above techniques
and the firing temperatures estimated. The samples have been grouped on archaeological grounds
according to Mrs Caskey's classification. It is interesting to observe the consistency of firing
temperatures within each group. Although in general the firing temperatures are not sufficiently
different to indicate different technologies from group to group the similarity of firing temperatures within each group emphasises probably the slightly different prevailing firing conditions and seem to verify to a very good degree the archaeological classification.
In view of the overall size of the statues one may resonably expect firing temperature
Table 2
Results on Ayia Irini terracotta statues
Colour
Dehydroxylation
Vitrification
Group I
TC5
TC11
TC14
TC18
TC19
Dark brown
Grey
Red-grey
Redgrey
Red
Complete
Complete
Complete
Complete
Complete
IV
IV
IV
IV
IV
Group 3 , 4 , 3 / 4
TC4
TC7
TC12
TC17
TC15
Red brown
Red brown
Red brown
Red brown
Red
Incomplete
Incomplete
Incomplete
Incomplete
Complete
NV
NV
Group 5
TC13
Redgrey
Complete
IV
750-800
Group 6
TC6
Grey
Complete
IV
750-800
Group 8
TC1
TC3
TC8
TC9
TClO
TC16
Grey
Dark brown
Redgrey
Dark brown
Grey-red
Dark brown
Complete
Complete
Complete
Complete
Complete
Complete
NV
NV
NV
NV
NV
NV
650-750
650-750
650-750
650-750
650-750
650 -750
Group 15
TCla
TC2a
Brown
Red
Complete
Complete
IV
IV
750-800
750-800
Sample
Nv
NV
NV
Firing temp. (" C )
750-800
750-800
750-800
750-800
750-800
< 650
< 650
< 650
< 650
650-750
198
Y. Maniatis, A. Katsanos and M. E. Caskey
differences within a single statue. However, this does not seem to be the case. Several samples
which were prepared from the same fragment (average size of fragments: 3 x 2 x 1 cm) did not
show any significant variation in firing temperature. Similarly fragments which have a certain
probability of having come from the same statue are fired t o the same temperature. For
example, samples 3 , 8 and perhaps 16 probably might have come from one statue (no 8-2
Caskey 1982). Also samples 9 and 10 are probably from the statue 8-1, and samples 7 and 1 2
are probably both from statue 4-1. In all these three cases the firing temperatures in each
group are the same. However, due t o the very fragmentary nature of the statues more detailed
investigation of the firing temperature differences was not really possible.
CONCLUSIONS
The main conclusions of thus work can be summarised as follows. The combination of SEM
and infrared spectroscopy proved t o be very useful for assigning firing temperature ranges in
these low-fired sherds while the SEM by itself could only give upper limits for the unvitrified
ceramics The scientific work which was done objectively (i.e. without any prior knowledge of
archaeological groupings) coincided excellently with Mrs Caskey’s grouping derived from pure
archaeological observations based on the technique of building, the fabric and the formal
characteristics of the figures. The higher and lower firing temperature groups were thus
archaeologically predicted. However due to the very low firing temperatures estimated the use
of kilns seems rather unlikely.
The differences in firing temperatures are not appreciable, taking into account. that statues
of this size are subject to uneven firing but the consistency within each group is an encouraging
demonstration of the agreement between very precise archaeological observation and scientific
examination.
ACKNOWLEDGEMENTS
We would like to thank Dr R. E. Jones of the British School of Archaeology at Athens for helpful discussion
on the composition of local clays and fmally the Physics Department of the Agronomy School of Athens for
the use of their SEM.
REFERENCES
Caskey. M. E., 1982, Keos 11. The Temple at Ayia Irini Part I. The Statues, Amer. School of Classical Studies,
Princeton, in press.
Farmer, V . C . , 1979, The Role of Infrared Spectroscopy in a Soil Research Institute, European Spectroscopy
News 25, pp. 25-27.
Grim. R. E.. 1968. Clay Minerology. McGraw-Hill, New York.
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histr. & hleth. 137, pp. 119-124.
Katsanos,A. e t a l . . 1978, Sensitivityof the External Beam Technique, Nucl. Instr. & Meth. 149, pp. 469-473.
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