image/svg+xml
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XII/2/2021
INTERDISCIPLINARIA ARCHAEOLOGICA
NATURAL SCIENCES IN ARCHAEOLOGY
homepage: http://www.iansa.eu
Orientation Patterns Characteristic for the Structure of the Ceramic Body
of Wheel-thrown Pottery
Richard Thér
1*
, Petr Toms
2
1
Department of Archaeology, Philosophical Faculty, University of Hradec Králové, Rokitanského 62, 500 03 Hradec Králové, Czech Republic
2
Private researcher, Machovská Lhota 71, 549 63 Machov, Czech Republic
1. Introduction
During the past decade, we have been developing
a methodology based on quantifcation of the orientation and
alignment of the components of a ceramic body as one of
the principal features refecting pottery-forming techniques
that are theoretically observable on every sherd (Thér,
2016; Thér
et al.
, 2019; Thér and Toms, 2016). Many of the
phenomena that occur on the surface of pottery fragments
and can be related to pottery-forming practices are randomly
preserved, and their interpretation is further complicated by
the common practice of combining several techniques during
the forming and fnishing of vessels. One diagnostic attribute
can, at least theoretically, be observed on every ceramic sherd
– the orientation of the structure of the ceramic body. The
relationship between forming techniques and the orientation
of the components of the ceramic material has long been
recognised (Balfet, 1953; Bordet and Courtois, 1967; Felts,
1942; Giford, 1928; Linné, 1925, p.33; Shepard, 1956,
pp.183–184). The application of physical force to the plastic
clay during forming is the main factor afecting the alignment
of the components. The resulting orientation and alignment
are characteristic of each forming method, although some
orientation patterns might result from more than one
fabrication process (for an overview of the assumptions for
particular techniques see Berg, 2008, Figure 1; Carr, 1990;
Courty and Roux, 1995, Table 1; Livingstone Smith, 2007,
pp.88–146; Middleton, 2005, Figure 4.8; Pierret, 1995,
pp.46–50; Roux, 2019, Figure 3.20; Rye, 1981, pp.58–89;
Thér, 2020, Figure 9; Whitbread, 1996).
Measurement of the orientation refnes the analysis of
preferred orientation by defning the exact intervals of
orientation variability for the individual forming techniques
and their combinations. For the measurements, we selected
two basic sections: sections perpendicular to the wall
surface in the plane parallel to the vessel height (hereinafter
referred to as a
radial section
) and sections tangential to the
vessel wall cut through a core zone of the wall (hereinafter
referred to as a
tangential section
). Originally, we captured
three transects approx. 6 mm wide in each thin section at
a magnifcation of 40 times in plane-polarised light using
a standard petrographic microscope. The resultant images
have a resolution of 1.09 μm. Then inclusions and voids were
extracted using object extraction and separation methods in
Volume XII ● Issue 2/2021 ● Pages 143–154
*Corresponding author. E-mail: richard.ther@uhk.cz
ARTICLE INFO
Article history:
Received: 19
th
February 2021
Accepted: 6
th
October 2021
DOI: http://dx.doi.org/10.24916/iansa.2021.2.3
Key words:
orientation analysis
wheel throwing
pottery forming
image analysis
thin section petrography
ABSTRACT
The described analysis follows recent fndings related to the orientation of particles and voids in
a ceramic body that is characteristic for wheel-made pottery. The analysis is focused on the potential
variability within wheel-throwing method and is based on an experimental collection that combines the
factors of the experience and motor habits of individual potters and the vessel shape. The orientation of
the components of a ceramic body is calculated for two sections: radial and tangential. The sections are
analysed using optical microscopy. The calculated orientation and alignment refect the throwing style
of potters using the same forming method.
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144
Table 1.
Orientation analysis results for experimental samples taken in tangential and radial sections. MD – Mean direction, CSD – Circular standard
deviation.
Sample
Min.
thickness
Max.
thickness
Dif. in
thickness
ShapeAuthorWheel
Radial sectionsTangential sections
MDCSDMDCSD
1379749101113BowlHenryMotorised735
28
36
2
4048
5001953BowlHenryMotorised5331930
339455125
1180
BowlHenryMotorised33627
38
4
48065807
1001BowlHenryMotorised3352731
5
4833
5617
784
BowlHenryMotorised3394123
65022
5587
565BowlHenryMotorised4353437
7
3809
4265456BowlHenryMotorised4392231
8
34924377
885
BowlHenryMotorised136
38
37
936724415743BowlHenryMotorised4332534
10
4080
4550470BowlHenryMotorised5335131
114026
4318
292BowlHenryMotorised733
38
35
1240434393350BowlHenryMotorised1354231
13
3830
4021191BowlHenryMotorised13239
38
1436723979307BowlHenryMotorised6314235
15
3784
4373
589
BowlHenryMotorised7302330
1636164229613Conical v.HenryMotorised15
28
2133
1733113742431Conical v.HenryMotorised19263734
18
35104471961Conical v.HenryMotorised14273135
19437256511279Conical v.HenryMotorised143439
38
20395651561200Conical v.HenryMotorised9334533
2140405329
1289
Conical v.HenryMotorised13323535
2243954700305Conical v.HenryMotorised3042
18
17
2339344593659Conical v.HenryMotorised24391921
244197
4538
341Conical v.HenryMotorised25401920
2544464970524Conical v.HenryMotorised13293231
2645495163614Conical v.HenryMotorised15
28
4341
2744765379903Conical v.HenryMotorised143143
38
28
321351751962Conical v.HenryMotorised17352324
2945545529975Conical v.HenryMotorised22322622
30461759771360Conical v.HenryMotorised16332629
31
2680
3270590BowlPeterMotorised5292933
323150317727BowlPeterMotorised53216
38
3331513617466BowlPeterMotorised
8
321934
3439714362391BowlPeterMotorised9293736
3532944134
840
BowlPeterMotorised
8
324540
363417
3859
442BowlPeterMotorised10304740
3737434146403BowlPeterMotorised0
38
24
28
383658
4372714BowlPeterMotorised232
38
43
393666
4086
420BowlPeterMotorised
8
35
28
30
40
3738
4265527BowlPeterMotorised
8
33
18
29
41
3598
4154556BowlPeterMotorised11342433
42
38714282
411BowlPeterMotorised12312432
43
3087
42341147BowlPeterMotorised7
38
2032
443691
4187
496BowlPeterMotorised9
38
3225
453727
4185458
BowlPeterMotorised11342726
46
4849
5931
1082
Conical v.PeterMotorised13372120
47
4885
5,10E+03215Conical v.PeterMotorised12
28
2624
48
42275013
786
Conical v.PeterMotorised6303523
4940945015921Conical v.PeterMotorised12302130
5045505016466Conical v.PeterMotorised36452130
5146435404761Conical v.PeterMotorised
8
343227
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Sample
Min.
thickness
Max.
thickness
Dif. in
thickness
ShapeAuthorWheel
Radial sectionsTangential sections
MDCSDMDCSD
5246205395775Conical v.PeterMotorised26342021
53
40384897859
Conical v.PeterMotorised223013
18
5444905162672Conical v.PeterMotorised
18
441326
5550616,15E+031091Conical v.PeterMotorised13
38
2229
5646195163544Conical v.PeterMotorised5272121
5746015274673Conical v.PeterMotorised11252124
583890
4120230Conical v.PeterMotorised
18
402627
5947165365649Conical v.PeterMotorised27512722
60
4783
5099316Conical v.PeterMotorised7313120
61
88249686862
Conical v.PeterFlywheel21341735
62
8832
9545713Conical v.PeterFlywheel193615
28
63
8981
9604623Conical v.PeterFlywheel2240
1828
64
8493
101591666Conical v.PeterFlywheel1336427
65
78708400
530Conical v.PeterFlywheel16351231
66
860711098
2491Conical v.PeterFlywheel17331731
67396560192054BowlThomasMotorised1030641
68
39165497
1581
BowlThomasMotorised12341639
69355455111957BowlThomasMotorised334532
70421664512235BowlThomasMotorised9351734
71434964752126BowlThomasMotorised
18
331132
723926
58161890
BowlThomasMotorised163517
28
73370271273425BowlThomasMotorised144013
28
74394766062659BowlThomasMotorised15371132
75377163352564BowlThomasMotorised23361132
76
4282
52911009BowlThomasMotorised9401933
774256
5658
1402BowlThomasMotorised13441331
78
4364
6078
1714BowlThomasMotorised11412029
79327357422469BowlThomasMotorised
8
32736
80
29545773
2819
BowlThomasMotorised
8
351135
81
354264772935BowlThomasMotorised1139935
82
6513
81941681
Conical v.ThomasMotorised13403539
83
62197205
986
Conical v.ThomasMotorised2241
18
36
84
6471
8063
1592Conical v.ThomasMotorised11361029
85
67737352579Conical v.ThomasMotorised15401737
86
67157233
518
Conical v.ThomasMotorised20
372436
87
71207343223Conical v.ThomasMotorised203716
38
88
7179
8131
952Conical v.ThomasMotorised19401130
89
7535
8166
631Conical v.ThomasMotorised16412937
907305
8214
909Conical v.ThomasMotorised19422537
91
6786
7729943Conical v.ThomasMotorised1139
8
39
9267757370595Conical v.ThomasMotorised
8
361640
9369697340371Conical v.ThomasMotorised
8
36
18
34
94792390601137Conical v.ThomasMotorised
8
3514
28
95747791141637Conical v.ThomasMotorised21332230
96
84768922
446Conical v.ThomasMotorised19331739
Table 1.
Orientation analysis results for experimental samples taken in tangential and radial sections. MD – Mean direction, CSD – Circular standard
deviation. (
Continuation
)
JMicroVision software (Roduit, 2014). Two basic measures
were chosen to express the object orientation: (a) mean
direction (MD) – average orientation of objects, and (b)
circular standard deviation (CSD) – the dispersion of the
values from the average (Fisher, 1993, pp.75–78; Mardia and
Jupp, 2000, pp.15–19).
In the frst experimental collection, we found several
signifcant markers distinguishing wheel fnishing,
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wheel shaping, and wheel throwing as basic levels of the
contribution of rotational movement in pottery forming
1
,
especially in the mean directions in core areas of radial
sections, in CSD in core areas of radial sections or the mean
direction in tangential sections (Thér, 2016).
In the second experimental dataset, we focused directly
on the distinctions among diferent uses of the potter’s
1
There are two basic ways to classify variants of the application of rotational
movement in the pottery-forming sequence. The frst approach classifes
individual combinations of the techniques applied at diferent stages of
the forming. The forming methods are then referred to as, for example,
wheel coiling or wheel moulding (Berg, 2009; Roux, 2019; 2017; Rückl
and Jacobs, 2016; Thér and Toms, 2016). An
alternative approach is to
separately defne the variants of the use of rotational movement and defne
them independently of the other techniques (Berg, 2008; 2007; Choleva,
2012; Courty and Roux, 1995; Henrickson, 1991; Roux, 2003; Roux and
Courty, 1998; Thér, 2016; Thér
et al.
, 2017; Thér and Toms, 2016). The
diferences in the contribution of rotational movement to the whole forming
sequence are the main criterion in this classifcation:
(a)
Wheel fnishing
. The vessel is formed by some hand-building technique
and subsequently the rotational movement is used for surface modifcations
and minor shape corrections,
i.e.
only in the fnishing stage.
(b)
Wheel shaping
. A roughout of the vessel is formed by some hand-
building technique and subsequently rotational kinetic energy (RKE) is used
to shape and thin the vessel walls. This technique can be used in assembling
and fnishing the vessel.
(c)
Wheel throwing
. The entire forming sequence is performed using RKE.
The main interest of the orientation analysis is to defne the relation between
the contribution of rotational movement in forming and orientation patterns:
thus, we use the second approach to classifcation.
wheel. In this dataset, we evaluated the efect of the degree
of transformation of the clay mass, the shape of the vessel,
the velocity of rotation or the individual experience and
skills of the potter. The principal fnding of the analysis of
the second experimental collection was that the specifc
characteristics of the orientation of wheel-thrown samples
are developed especially in the lower parts of the vessels.
The signifcant diference between the results obtained from
lower and upper parts of the experimental vessels can be seen
especially in the tangential sections. The diference is due to
the fact that the lower part of the vessel undergoes a strong
transformation when the potter creates a basic form prepared
for lifting. While she/he lifts the clay mass upward, the rest
of the clay is lifted above the fngers but is not afected by
their movement (Thér and Toms, 2016, pp.38–39).
The analysis of the second experimental series also
confrmed the observation made in the frst experimental
series, namely that the upper ends of the objects in the
marginal zones of wheel-thrown
pottery incline inwards
towards the core of the wall (Figure 1). We called this
phenomenon “imbricate pattern” and suggested that
this pattern is caused by shear stress induced by upward
movements of the fngers during wheel throwing. The clay
mass in the margins moves more quickly during lifting than
the mass in the core of the wall. Therefore, marginal zones
can be seen as shear zones with a predominance of shear
stress. The comparison of internal and external areas shows
that the inclination of the inclusions and voids inwards is
more strongly developed in the external area. We explained
this phenomenon by the disproportion of the forces required
on the interior and exterior of the vessel, which causes larger
shear deformation on the exterior area of the vessel wall and
subsequently a more pronounced imbricate pattern in this
area (Thér and Toms, 2016, p.38).
In the third experimental series described in this study,
we focused solely on the orientation patterns resulting from
wheel throwing and especially on those variables whose
signifcant efect became the subject of hypotheses after
evaluating the previous series.
a) Above all, the shape of the vessel is important. The
analysis suggested that the shape signifcantly infuences
the orientation parameters. Samples taken from the oblate
ellipsoid fashioned in the second experimental series showed
below-average CSD values in radial sections from the lower
parts of the vessels but, more importantly, a signifcant
increase in CSD and lesser deviation from the horizontal
axis in tangential sections (Thér and Toms, 2016, Figures 5
and 7). The distortion from typical wheel-throwing values
for conical shapes could be hypothetically proportional to
the degree of transformation that is required to fnish the
shape of the vessel extra to the lifting of the clay.
b) The second experimental series also showed that the
orientation patterns refect the equilibrium established between
the potter´s actions and tools she/he uses during forming.
If the potters use an unfamiliar clay or rotational device or
throw an unusual shape, they disturb the equilibrium gained
by experience and thus also the alignment typical for the
Figure 1.
Imbricate pattern – orientation pattern typical for wheel throwing
observed in radial sections. The upper ends of the objects in the marginal
zones of wheel-thrown pottery incline inwards towards the core of the wall.
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technique. This especially applies to the beginner for whom
all the components of the technique are new (Thér and Toms,
2016, Figure 7). In this current, third experimental series we
compared three professional potters who routinely produce
pottery, to see whether the results are comparable when the
potters have (a) a similar, high level of skill, (b) create shapes
that do not difer signifcantly from what they are used to
forming on a wheel, and (c) use familiar tools,
i.e.
potters are
in equilibrium with their working environment.
2. Materials and method
The third experimental collection is focused on the variability
of orientation patterns within the wheel-throwing method.
So far, one principal experienced potter with 23 years of
experience in wheel throwing, Peter Toms, was employed in
our experiments. Along with Petr Toms (hereinafter referred
to as Peter) we included two other professional potters: Jiří
Lang (hereinafter referred to as Henry) and Tomáš Macek
(hereinafter referred to as Thomas).
Two diferent vessel shapes were replicated: a simple
conical vessel 180 mm in height and 200 mm in diameter at
the top and an S-shaped bowl 85 mm in height and 200 mm in
diameter at the top (depicted in Figure 2). The S-shaped bowl
was chosen because, in our application of the methodology,
we are dealing mainly with Late Iron Age pottery in Central
Europe, and this is the most common shape of wheel-made
pottery in this context.
Each potter formed 15 slightly conical pots and 15 S-shaped
bowls. The target wall thickness for all the containers was
5 mm. No other parameters of the forming method were
specifed in order not to force the potters to employ motions
that are not “natural” for them. All the potters used their
wheels (motor-driven) and the same fne-grained commercial
clay – Witgert 10. The experimental collection was created
during one session in one pottery workshop after the potters
became acquainted with the selected pottery shapes. The
speed of the wheels was measured by a laser tachometer.
The dataset was complemented by six conical vessels
thrown by Peter on a replica of a fywheel made of a wooden-
spoked wheel. The device is located in the Archaeological
park of prehistory in Všestary (Czech Republic). Peter
does not work on this wheel on a regular basis and there
was a minor technical problem related to ftting the wheel
socket in the axis which caused vibrations of the wheel when
a certain speed was reached.
Two oriented thin sections were cut from the lower
body of each experimental vessel: tangential and radial
(Figure 2). The entire area of each thin section was recorded
at a magnifcation of 200× using a Keyence VHX6000
digital microscope. The resultant images have a resolution of
1.11 μm. The analysis followed the published methodology
(Thér, 2016; Thér and Toms, 2016), except for the software
treatment. The components of the ceramic materials were
extracted using automatic area measurement tools available
in the Keyence VHX6000 measurement software. The range
of threshold values chosen to separate inclusion and void
representations was based primarily on colour saturation,
which shows the best results for the thin sections with
uneven thickness (resulting in uneven brightness of the
captured image).
The extracted objects in the radial sections were analysed
only in the external zones of the section (one-third of the
thickness adjacent to the outer edge). The focus on the
external area follows the results of the analysis of the
Figure 2.
Experimentally-replicated vessels’
shapes with the location of tangential and
radial sections.
Figure 3.
Descriptors of the separate objects relevant to the analysis.
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second experimental series which showed that the typical
imbrication pattern is more strongly developed in the external
area (Thér and Toms, 2016, Figure 4). The extracted objects
were characterised by a set of descriptors relevant to the
analysis (Figure 3): a) maximum diameter – the maximum
length between any two points that lie on the inner perimeter
of the object; b) minimum diameter – the minimum possible
distance between two parallel lines on either side of the
object, this is calculated as the distance between the pixels
that each of the two lines touches; c) elongation – aspect
ratio of the object (maximum diameter/minimum diameter);
d) orientation – the angle between the object’s maximum
diameter axis and the horizontal axis read clockwise for
tangential sections and the angle between the object’s
maximum diameter axis and the vertical axis read counter-
clockwise for radial sections.
Two basic measures were chosen to express the object
orientation: (a) mean direction, and (b) circular standard
deviation (CSD) (Fisher, 1993, pp.75–78; Mardia and
Jupp, 2000, pp.15–19). The raw data are plotted in a polar
coordinate system. Each point in the diagram is determined
by an angle from a reference direction which represents the
mean direction of the objects of the given sample and the
distance from the centre of the circle which represents the
CSD values. The calculated orientations are an axial type of
data. Axial data consist of an undirected line – either end of
Figure 4.
Orientation of inclusions and voids in tangential sections.
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the line could be taken as the direction; therefore, the data
are represented by both possible directions,
i.e.
, each sample
is plotted by a pair of points.
3. Results
The work of each of the potters can be characterised by
a slightly diferent orientation pattern (all the measurements
are summarised in Table 2). Peter’s conical vessels show
a coherent group corresponding to the previous fndings in
orientations and alignment in tangential sections (average
deviation from horizontal axis 21° and CSD 24°), the
bowls exhibit similar orientation (average MD 27°), but
a signifcant increase in CSD (33° on average) with extremes
exceeding 40° (Figure 4). A signifcant diference can also
be observed in the radial sections. The conical vessels have
signifcantly more developed inward inclination (15° on
average) compared to the bowls (8° on average; Figure 5).
While the thickness of the conical vessel walls (measured
in the area of the sample) roughly corresponds to the
specifed thickness (4.8 mm on average, standard deviation
of 0.4 mm), the wall thickness of the bowls is signifcantly
lower (3.8 mm on average, standard deviation of 0.3 mm;
Figure 6). Throwing of pots on the fywheel results in
a decrease in the deviations from the horizontal axis (average
MD 16°, average CSD 30°). The thickness of the walls
(9.2 mm on average, standard deviation of 0.6 mm; Figure 6)
demonstrates the difculty that the potter encountered when
using non-standard and technically-unadjusted equipment.
Conical vessels and bowls cannot be reliably diferentiated
in the production by Henry. Both show a higher average
deviation from the horizontal axis (average MD: conical
v. 31°, bowls 34°) than Peter’s vessels. The average CSD
is similar (conical v. 33°, bowls 34°) and comparable with
the bowls produced by Peter. Only a small proportion of
the conical vessels exhibit CSD below 30° (Figure 4). In
contrast, there is a diference in the inward inclination
between conical vessels and bowls in the radial sections.
The diference is similar to that of Peter’s samples but more
pronounced: conical vessels – 17° on average, bowls – 4° on
average (Figure 5). The wall thickness of the conical vessels
(4.5 mm on average, standard deviation of 0.5 mm) and bowls
(4.4 mm on average, standard deviation of 0.5 mm) is similar
and corresponds with the assigned thickness (Figure 6).
Both the shapes fashioned by Thomas show lower mean
deviation from the horizontal axis than the vessels fashioned
by the previous two potters and there is a signifcant
diference between them in this respect. The bowls exhibit
lower deviation than the conical vessels (conical v. 17° on
average, bowls 11° on average). Thomas’ vessels are very
similar in alignment (average CSD: conical v. 33°, bowls 34°)
to those of Henry (Figure 4). No signifcant diference
can be seen in the radial sections: the average MD of the
conical vessels is 15° and bowls 12° (Figure 5). The conical
vessels are signifcantly thicker than required (7.5 mm on
average, standard deviation of 0.6 mm). The bowls have
an average thickness of 4.9 mm (standard deviation of
0.3 mm; Figure 6). The signifcantly higher diference in the
wall thickness compared to other assemblages refects the
unevenness of the walls in the lower parts of the bowls (the
walls taper upwards; Figure 7).
4. Discussion
The results point to interesting diferences among the
potters. All three potters came from diferent learning
environments. They used motor-driven potter’s wheels
(except for the manually-driven fywheel). Peter and Henry
Table 2.
Descriptive statistics of orientation, alignment, and wall thickness of experimental samples according to the observed variables.
PotterHenryPeterThomas
ShapeBowlConical v.BowlConical v.BowlConical v.
WheelMotorisedMotorisedMotorisedMotorisedFlywheelMotorisedMotorised
Number of Observations1515151561515
Av. thickness (mm)4.44.5
3.8
4.99.257.5
Standard deviation of thickness (mm)0.50.50.30.40.50.30.6
Av. diference in thickness (mm) 0.70.90.50.71.12.20.9
Tangential
sectons
Mean Vector (µ)
32.983
30.411
28.446
23.2113.90212.405
18.673
Circular Standard Deviation
8.9779.1859.2876.108
5.109
4.4877.078
99% Confdence Interval
(–/+) for µ
26.34923.623
21.58318.695
6.742
9.087
13.441
39.61737.19935.30927.72621.06215.72223.905
Radial
sections
Mean Vector (µ)
3.988
17.306
7.585
15.473
17.688
11.97615.419
Circular Standard Deviation
2.082
5.3513.143
8.495
3.0554.6374.921
Standard Error of Mean0.5971.5360.9022.4371.6621.3311.412
99% Confdence Interval
(–/+) for µ
2.44913.355.2629.19413.406
8.54811.781
5.52721.2629.90921.75121.9715.40419.057
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Figure 5.
Orientation of inclusions and voids in radial sections.
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used wheel variants with a motorised fywheel which
makes the regulation of rotation speed more difcult. Their
performance is closer to kick wheels with characteristic
speed oscillations. Thomas used a direct-drive wheel where
the wheelhead is directly connected to the motor and speed is
regulated by the foot pedal allowing maintenance of constant
rotation speed. There were no apparent diferences in their
throwing styles with one slight exception which will be
discussed later. Progress of wheel velocity during forming
and time spent on manufacture was measured (Figure 8).
Peter works signifcantly faster than the other two potters
with lower wheel velocity (thus his work is the most efcient
in terms of energy expenditure). The need for fewer moves
to achieve the same shape is refected by the low CSD in
the tangential sections of samples taken from Peter’s conical
vessels compared to the other conical vessels. The bowls
were generally thrown in a shorter time because of their
smaller size. More interestingly, the velocity decreases more
rapidly during the forming of bowls than of conical shapes.
The wider shapes require more careful lifting to prevent
disruption or collapse of the shape.
The efect of the shape is partially independent of
an individual’s throwing style and experience. The observed
phenomena basically conform to the results of analysis
of the second experimental collection: the more intricate
the shape, the greater the transformation (or disruption of
typical orientation). However, the efects vary from potter
to potter. The distortion from typical wheel-throwing values
for conical shapes could be hypothetically proportional
to the degree of transformation from the roughout to
the fnal shape. A roughout is formed in the frst stage of
throwing. In this stage, all the basic lifting of the clay mass
is completed. Lifting causes development of the orientation
patterns typical for wheel throwing. In the subsequent
stage, the lifted clay mass is transformed into the required
shape. This transformation is performed while the wheel is
still spinning; pressure is combined with rotational energy,
which theoretically causes (a) thinning of the vessel wall,
(b) transformation of the object orientation resulting in
lowering of the average angle (reorientation towards the
horizontal axis) and an increase in CSD in the tangential
section, and (c) greater parallel alignment of the objects to
Figure 6.
Wall thickness in the sample
location. JLB – bowls thrown by Henry;
JLC – conical vessels thrown by Henry;
PTB – bowls thrown by Peter; PTC – conical
vessels thrown by Peter; PTF – conical
vessels thrown by Peter on a fywheel; TMB
– bowls thrown by Thomas; TMC – conical
vessels thrown by Thomas.
Figure 7.
Diference in wall thickness in
the sample location. JLB – bowls thrown
by Henry; JLC – conical vessels thrown
by Henry; PTB – bowls thrown by Peter;
PTC – conical vessels thrown by Peter;
PTF – conical vessels thrown by Peter on a
fywheel; TMB – bowls thrown by Thomas;
TMC – conical vessels thrown by Thomas.
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152
the wall axis in perpendicular sections,
i.e.
, less profound
imbrication patterns. However, there is another way to form
more intricate shapes. For some potters, the distinction
between the lifting of a roughout and its transformation into
a fnal shape is rather theoretical. They continue lifting while
forming the fnal shape and the two phases are not strictly
separated. This approach is essential to achieving regular
wall thickness. Consequently, in these cases, the orientation
should not be strongly afected by the further transformation
of the body.
All three potters involved in this experiment frst throw the
conical roughout and then widen it into the shape of a bowl.
However, while Peter and Henry begin to widen the shape in
the relatively early stage of the throwing, Thomas keeps the
shape closed signifcantly longer. The potters demonstrate
three diferent sets of efects, refecting diferent throwing
styles or skills. Peter’s bowls are 23% thinner than his conical
vessels (Figure 6). A signifcant increase in CSD in the
tangential sections (Figure 4) was observed with a decrease
in the inward inclination in the radial sections (Figure 5).
On the other hand, the bowls show a similar deviation from
the horizontal plane as the conical shapes (Figure 4). The
thickness of Henry’s bowls is similar to that of his conical
vessels (Figure 6). There is no signifcant diference in object
orientation in the tangential sections (neither in MD, nor
in CSD), but Henry’s bowls and conical vessels show the
highest diference in inward inclination in the radial sections
(Figure 5). Thomas’s bowls are 34% thinner than his conical
vessels (Figure 6) and the wall thickness is very uneven
(Figure 7). Signifcantly lower deviation from the horizontal
axis was observed, but no increase in CSD (Figure 4) and
there is also no signifcant diference in orientation in the
radial sections (Figure 5). None of the described patterns
can be unequivocally related to the hypothetical efects of
diferent throwing habits. For example, the lower deviation
from the horizontal axis in the case of Thomas’s bowls and
the diference in thickness compared to conical vessels could
be attributed to his habit of keeping the shape closed till
the fnal stage of throwing, but there is no increase in CSD
in tangential sections or decrease in imbrication pattern in
radial sections.
The potter’s experience is refected indirectly by the
deviation from the specifed parameters of the experimental
forming. The thicker walls of the conical shapes and uneven
thickness of the bowl’s walls testify to the fact that Thomas
had difculty achieving the required parameters. This
corresponds with the observation (not exactly measured)
that the shapes of Thomas’s vessels visibly deviated from
the template vessels. Thomas confrmed that, at the time
of the experiment, he did not throw pottery regularly and
intensively and consequently he lacked a corresponding
routine. Also, the thickness of the conical vessels thrown on
the fywheel refects Peter’s lack of familiarity with this type
of wheel and probably also the technical problems associated
with the device, causing unstable rotation. In both cases,
lower deviation of the object orientation from the horizontal
axis is characteristic. Consequently, this efect cannot be
associated either with the vessel shape itself or with any
other considered variables,
e.g.
, speed of the rotation.
The results of the analysis of this experimental dataset
have signifcant consequences for the application of this
methodology to archaeological pottery. The idea that the
orientation pattern is consistent for wheel throwing in
general (as for a forming method highly constrained by
the forces employed during forming) irrespective of the
potters’ individual motor habits is no longer valid. The
results show that we have to consider a wider range of the
orientation values for wheel throwing and there is a partial
overlap of values with combined forming methods. The
measurements on tangential sections showing the deviation
from a horizontal plane ranging between 15–35° and CSD
20–30° can be reliably interpreted as a result of wheel
throwing. These intervals delimit the zone into which no
data from other experimentally-tested forming methods
have entered (Thér and Toms, 2016, Figure 6). However,
CSD measurement results ranging between 30–40° cannot
Figure 8.
Averaged development of velocity
of rotation of the wheels used by the potters
in the experimental replication.
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Richard Thér, Petr Toms: Orientation Patterns Characteristic for the Structure of the Ceramic Body of Wheel-thrown Pottery
153
be interpreted unambiguously as they may refect both
an individual throwing style and combined techniques
employing wheel shaping. In this case, evidence independent
of orientation measurements is required to distinguish
between the two variants of the potter’s wheel contribution.
Apart from traditional macrotrace analysis (Arnold, 1993;
Choleva, 2012; Doherty, 2015; Dupont-Delaleuf, 2011;
Gelbert, 1994; Jefra, 2013; Knappett, 1999; Méry
et al.
,
2012; Roux, 2019; 1994; Roux and Courty, 1998; Rückl
and Jacobs, 2016), which has limited value in that the
technological context where the wheel-made pottery is made
of fne-grained ceramic materials and the surface is carefully
fnished, we suggest combining two scales of structural
analysis. The microscale imaging that reaches a resolution
of a few micrometres can efectively capture an area of
2 cm
2
, which is given by (a) the size of thin sections and the
limitations in positioning planar tangential sections within
curved vessel walls or (b) computed tomography limits in
the combination of resolution and size of the samples. This
type of analysis allows an accurate estimate of inclusion and
void orientation, but only locally. We propose to combine
microscale analysis with imaging at a smaller scale to
capture a larger area of the sample. At this scale, the accurate
measurement of orientation is complicated, especially when
analysing fne-grained ceramics, but other structural features
can be observed, especially structural discontinuities
refecting segmental forming techniques (Thér, 2020). By
such a combination, the potential to diferentiate individual
techniques will be increased and, given the results of the
described analysis, we can consider tracking the throwing (or
more generally forming) style of potters based on structural
analysis of their products. The most suitable technique
for imaging the structure on a smaller scale seems to be
computed tomography (Bernardini
et al.
, 2019; Gibbs, 2008;
Gomart
et al.
, 2017; Kahl and Ramminger, 2012; Karl
et
al.
, 2014; Kozatsas
et al.
, 2018; Kulkova and Kulkov, 2016;
Machado
et al.
, 2013; Sanger
et al.
, 2013; Sanger, 2016).
5. Conclusion
Analysis of the experimental collection of pottery made by
three professional potters using wheel throwing revealed
imprints of individual motor habits captured by the
orientation analysis. It draws attention to the signifcance
of individual style or the specifcs of individual motor
habits in technological studies. The analysis demonstrates
that the individual motor habits can signifcantly afect the
orientational pattern even for a forming method that seems
to be very deterministic in terms of the forces employed
during forming. More attention must be paid in the future
to identifcation and description of the diversity of the
modalities of wheel throwing and subsequent determination
of their efects in the archaeological record. This will help to
defne the limits of this forming method (and especially the
limits of its efects observable in the archaeological record),
which is crucial both for its distinction from other forming
methods utilising rotational movement and for understanding
the dynamics of the evolution of wheel throwing.
Acknowledgements
The research described in this paper was completed with
support from the project “Technological changes in pottery
manufacture in the context of social transformations during
the La Tène period in Bohemia” (project 19-21146S),
fnanced by the Czech Science Foundation. We would like
to thank Madeleine Štulíková for her assistance in correcting
the English grammar and to Ina Berg, Caroline Jefra, and
Chase A. M. Minos for their helpful comments.
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