EXPERIMENTING WHEEL-COILING METHODS

Pour citer cet articleJeffra C., 2015, “Experimenting wheel-coiling methods,”The Arkeotek Journal, 2015, n°2,www.arkeotekjournal.org.

Mots-clés

ceramic technologyexperimental datawheel coiling methods

INTRODUCTION

In the archaeology of Middle Bronze Age Crete and Late Bronze Age Cyprus, it has been observed that the pottery wheel came into use, although it is unclear whether either case is of internal development or external technological borrowing. In both cases, scholarship has traditionally identified the earliest use of the wheel with the wheel-throwing technique. This technological transition from hand-building to wheel-throwing vessels has been critically re-evaluated in Levantine contexts through the work of Roux and colleagues. As a result, the material from both Crete and Cyprus merited closer examination to assess whether potters were wheel-throwing their products, or if they were using wheel coiling methods which combined existing hand-building practices with novel ones based on the use of rotative kinetic energy (RKE). The experiment described (conducted during the completion of the author’s doctoral research, see Jeffra 2011) provides a type set of vessels against which Bronze Age material could be compared.

This experiment demonstrates that the relationship between RKE forming method and the group of macroscopic traces highlighted by Roux and Courty (1998) is not affected by the shape of vessels. Within the experiment it had only a minimal impact on the way that traces manifested, notable in the fact that some shapes exhibited some types of diagnostic macroscopic traces, while other shapes did not. Finally, this experiment shows that in many cases individual traces could be seen on vessels made according to different wheel coiling methods. Instead, attention should be paid to the group of traces present on a vessel for greater certainty in identification. For example, rilling is ubiquitous in the RKE-formed vessels; it alone cannot form a reliable basis for method-specific identification. The combination of rilling with coil seams (when their relative orientation is taken into consideration) does, however, support specific method 3 identification.

EXPERIMENTING WHEEL-COILING METHODS

The experiment

P0/1 Experimental objectives and protocols

Objectives

  • To identify macroscopic traces which correspond to specific methods of wheel-coil vessel manufacture
  • To explore the influence of vessel morphology on location and type of macroscopic trace evidence

Protocol

Key to the methodology used is the demarcation of four specific types of wheel fashioning techniques, successively incorporating greater proportions of RKE through the process (Roux and Courty 1998, 748-750, fig. 1). Although four separate methods were described by Roux and Courty, only methods 1-3 were represented in the experimental typeset. Method 4 was not utilised in this study for a number of reasons. First, method 4 is in use in Crete at Thrapsano, which provides an ample representation of the ways in which macroscopic traces manifest. Second, method 4 is particularly well-suited to very large vessels (such as pithoi), a vessel size which was not addressed within the parameters of this study. Finally, in small vessels, the division between method 3 and method 4 is unclear; with small vessels, a single coil may easily provide enough clay to produce the entire height of a vessel’s wall.

It is important to note that when the experimental typeset vessels were formed, the surfaces of those vessels were left entirely unaltered. The tools used included only a pottery wheel, the potter’s hands, a sponge for applying/removing water and finishing the rim, and a wire to trim rims and cut vessels from the wheel surface. In this way, vessel surfaces should not include unrepresentative macroscopic traces from tools not verified archaeologically. The lack of surface modification after forming allows vessels to present the full range of possible macroscopic traces, thereby increasing the probability that such traces are recognised archaeologically despite finishing and decoration operations known to exist in the archaeological material.

Vessels were fired in a programmable electric kiln, actively increasing temperatures over 7 hours and reaching 1000 degrees centigrade (see firing curve in Figure 1).

Figure 1. Firing curve showing the rate at which experimental vessels were fired.

Although the specific gestures used for the implementation of the various forming methods used differ, the way in which they are described below has been standardised. Discussions of coil joining and wall thinning therefore follow the format illustrated in Figure 2.

Figure 2. Diagram illustrating the terms used to describe coil joining and wall thinning action directionality.

P0/2 Experimenting Method 1

Method 1 involves minimal use of RKE; the separate actions of forming the coils, joining the coils, and thinning the coils are each completed with the use of discontinuous pressures (i.e. without RKE, after Courty and Roux 1995, 22). During the final stage of shaping, the coil-built roughout is then subjected to continuous pressures through the use of RKE. This late stage application of RKE, according to Roux and Courty (1998, 751), leads to slight modification of vessel wall surfaces, as the walls would have already been subjected to discontinuous pressures.

Although some procedures used were specific to the shapes formed, all vessels formed using method 1 were constructed of coils which were 1.5 times thicker than the final vessel wall thickness. In coil joining and wall thinning, vessels were subjected to slightly different gestures based on the shape or size of the vessel. As such, these stages best described within vessel shape sub-sections.

In all cases, vessel shaping was undertaken with RKE, in an anti-clockwise direction. Shaping was achieved by wetting the vessel surface from the sponge and then applying pressure to the wall as it glided between fingers. The shaping process was started at the vessel base, and gradually hands were raised while continuing to apply pressure in order to slowly rise to the upper body of the vessel.

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Cups

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Cups

In all cases of cups, the direction of coil joining was clockwise.

While the walls of straight-sided cups (Figure 3) and carinated cups (Figure 5) were thinned in a clockwise direction, those of rounded cups (Figure 4) were thinned in a left-rising direction for method 1 forming.

Figure 3. Straight-sided cup formed using method 1. Vessel number 1.

Figure 4. Rounded cup formed using method 1. Vessel number 26.

Figure 5. Carinated cup formed using method 1. Vessel number 41.

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Cups

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Bowls

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Bowls

For both the rounded bowls (Figure 6) and the carinated bowls (Figure 7), coils were joined in a left-rising direction.

Rounded and carinated bowls alike were thinned in a left-rising direction for method 1 forming.

Figure 6. Rounded bowl formed using method 1. Vessel number 56.

Figure 7. Carinated bowl formed using method 1. Vessel number 71.

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Bowls

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Jars

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Jars

Each type of jar (Figures 8-9) was constructed of coils joined in an upward direction.

As in the case of coil joining, wall thinning was consistent for both jar type, completed in a clockwise direction for method 1.

Figure 8. Rounded jar formed using method 1. Vessel number 101.

Figure 9. Conical-based jar formed using method 1. Vessel number 116.

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Jars

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Basins

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Basins

Coils for the basins (Figure 10) were joined in a left-rising direction.

Basins walls were thinned in a clockwise direction for method 1 forming.

Figure 10. Basin formed using method 1. Vessel number 86.

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Basins

P0/3 Experimenting Method 2

Method 2 incorporates the use of RKE earlier in the formation process. Forming and joining the coils are, as above, accomplished with the use of discontinuous pressures, while both thinning the coils and shaping the roughout would be done through the use of RKE. The earlier use of RKE in this method should strongly modify wall surfaces through the erasure of joins and wall thinning (Roux and Courty 1998, 751).

In the construction of the present experimental vessels, coils for method 2 construction were between 1.5 and 2 times the final wall thickness. Because method 2 vessels are formed using rotation for wall thinning and shaping, only the first stage (coil joining) varied in gesture by shape, and is described in separate sub-sections below.

Method 2 wall thinning was completed using RKE in a clockwise direction. Vessels were rotated slowly on the wheel surface and continuous pressures were applied, from lower wall to upper wall, with the fingertips. In all cases, shaping was undertaken with RKE, in an anti-clockwise direction. Shaping was achieved by wetting the vessel surface from the sponge and then applying pressure to the wall as it glided between fingers. The shaping process was started at the vessel base, and gradually hands were raised while continuing to apply pressure in order to slowly rise to the upper body of the vessel.

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Cups

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Cups

While the coils of straight-sided cups (Figure 11) formed with method 2were joined in a left-rising direction, the coils of rounded (Figure 12) and carinated (Figure 13) cups were joined in a clockwise direction.

Figure 11. Straight-sided cup formed using method 2. Vessel number 8.

Figure 12. Rounded cup formed using method 2. Vessel number 31.

Figure 13. Carinated cup formed using method 2. Vessel number 46.

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Cups

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Bowls

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Bowls

The coils forming both rounded (Figure 14) and carinated (Figure 15) bowls were joined in a left-rising direction for method 2 manufacture.

Figure 14. Rounded bowl formed using method 2. Vessel number 61.

Figure 15. Carinated bowl formed using method 2. Vessel number 76.

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Bowls

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Jars

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Jars

As was the case for jars made with method 1, those made with method 2 (Figures 16-17) were composed of coils joined in an upward direction.

Figure 16. Rounded jar formed using method 2. Vessel number 106.

Figure 17. Conical-based jar formed using method 2. Vessel number 121.

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Jars

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Basins

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Basins

Basins formed with method 2 (Figure 18) were constructed of coils joined in a clockwise direction.

Figure 18. Basin formed using method 2. Vessel number 91.

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Basins

P0/4 Experimenting Method 3

Method 3 involves discontinuous pressures for formation of coils only, a stage which is followed by joining and thinning of coils as a combined step with the use of RKE, before shaping of the roughout with RKE. The continuous pressures from RKE in this method strongly deform coils as well as wall surfaces, which should ultimately obscure patterns of coil joining (Roux and Courty 1998, 751).

Vessels constructed using method 3 were formed of coils which ranged between 2 and 3 times the final wall thickness. Because all stages of the forming process were completed with RKE, the discussion of gestures is consistent across shapes formed.

The direction of coil joining was uniformly in a clockwise direction. This was carried out using a ‘leapfrog’ approach (as illustrated in Figure 19), where the lowest coil of the vessel wall was first compressed at its widest point. Following this, the coil immediately above was then similarly compressed. Finally, the point at which these coils met, which had narrowed through the compression of coils, was subjected to continuous pressure in order to seal the coil seam. This process was repeated from lower wall to upper wall until all coils were joined.

Figure 19. Sequence of method 3 “leapfrog” coil joining using continuous pressures: a) joining and thinning the first coil; b) thinning the second coil; c) joining the two thinned coils; d) vessel profile following thinning and joining of first two coils.

Method 3 wall thinning and vessel shaping was completed using RKE in a clockwise direction. Vessels were rotated slowly on the wheel surface and continuous pressures were applied, from lower wall to upper wall, with the fingertips.

Results

P1/1 The wheel coiling - Diagnostic Features

A number of macroscopic traces were observed which related to the use of both RKE and non-RKE forming strategies. In most cases, however, it was the patterned combination of several traces which corresponded with specific forming methods. Those individual traces which were found in different combinations are :

- Rilling – The tiny bands of striations formed by the passage of fingers, sponge or tool over the vessel surface during rotational shaping.

- Coil seams – Roughly horizontal linear traces with a narrow V-shaped trench in profile, caused by the close proximity of two concave bands.

- Torsional deformations – Twisting deformation of the vessel wall caused by the excessive braking effect of hands or tools on the vessel body during rotation.

- Thickness discontinuities –Zones of thicker or thinner wall profile thickness, observable as discontinuous vertically, horizontally, or diagonally.

Figure 28. Straight-sided cup (vessel number 13) showing rilling, especially visible near the upper wall. Vessel number

Figure 29. Interior of a carinated cup (vessel number 51) showing a coil seam.

Figure 30. Torsional deformation of RKE vessels: a) Illustration of the opposing forces at work; b) Illustration of the possible deformation prior to vessel collapse or wall tearing.

Figure 31. Illustrated cross section of thickness discontinuities.

P1/2 The Method 1 - Diagnostic Features

1) Re-smoothed vertical fissures appear most likely due to the fact that method 1 vessels were formed of coils which had first been manipulated by hand. This would have diminished the moisture on the surface of each coil, relative to the moisture within the coil. As these were stacked and prepared for rotative shaping, the wall surfaces would become drier. During rotation, although water was added to the surface, only the outermost portion of the wall would be affected and shaping would split the less malleable layers within the wall profile. This would then be partially obscured by the moisture introduced for lubrication of rotational shaping.

2) The presence of diagonally-oriented thickness discontinuities is most likely in the case of method 1 vessels, due to the combination of coil joining and wall thinning undertaken without rotation. These actions tended to create vertical zones of thicker or thinner wall profile width which, when overlain by rotational shaping, took on a gentle diagonal aspect.

3) Marked depressions presenting a much gentler profile as depressions in the vessel wall overlain by shaping-related rilling. They are formed, in some cases, by heterogeneous discontinuous coil joining and wall thinning, primarily from the particular pressure of one or two fingers on the wall.

Figure 32A. Rounded cup (vessel number 27) showing a re-smoothed vertical fissure on the exterior vessel wall, visible in the right of the image.

Figure 32B. Carinated bowl (vessel number 73) showing a re-smoothed vertical fissure on the exterior wall, visible on the uppermost section of the sherd wall.

Figure 32C. Rounded bowl (vessel number 58) showing re-smoothed vertical fissures on the interior wall.

Figure 32D. Rounded jar (vessel number 102) showing re-smoothed vertical fissures on the exterior wall, particularly at the centre of the image.

Figure 32E. Basin (vessel number 90) showing a re-smoothed vertical fissure on the exterior wall, particularly on the left side of the image.

Figure 33A. Carinated cup (vessel number 41) with diagonally-oriented thickness discontinuities, particularly marked between the carination and the rim.

Figure 33B. Rounded cup (vessel number 28) with diagonally-oriented thickness discontinuities, most visible on the upper portion of the vessel wall interior.

Figure 33C. Carinated bowl (vessel number 72) with very gentle diagonally-oriented thickness discontinuities, most visible mid-way between the base and carination.

Figure 33D. Rounded bowl (vessel number 58) with diagonally-oriented thickness discontinuities, visible on interior wall surface.

Figure 33E. Rounded jar (vessel number 104) with diagonally-oriented thickness discontinuities, especially visible on the lower interior wall.

Figure 33F. Conical-based jar (vessel number 117) with diagonally-oriented thickness discontinuities visible on the interior wall.

Figure 33G. Basin (vessel number 88) with diagonally-oriented thickness discontinuities visible on the interior wall.

Figure 34A. Carinated cup (vessel number 43) showing depressions in the vessel wall overlain by shaping-related rilling on the vessel exterior.

Figure 34B. Straight-sided cup (vessel number 11) showing depressions in the vessel wall overlain by shaping-related rilling visible on the interior wall.

Figure 34C. Rounded cup (vessel number 30) showing depressions in the vessel wall overlain by shaping-related rilling visible on the interior wall surface.

Figure 34D. Rounded bowl (vessel number 30) showing depressions in the vessel wall overlain by shaping-related rilling visible on the exterior wall surface.

P1/3 The Method 2 - Diagnostic Features

1) A combination of generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling was most often seen on method 2-formed vessels. First of the morphological features included in this suite of traits are generalised, gentle thickness discontinuities, which were discontinuous on the vertical and the horizontal planes. As with method 1 thickness discontinuities, these were likely caused by the non-rotational joining of coils. Unlike in the case of method 1 vessels, there was less of a tendency for this trace to be diagonally-oriented along the vessel wall. What is observable and more patterned is an overlaying convex/concave morphology, visible as gentle waves which would have been produced by the slow progress of rotational thinning and shaping. As such, the crests of these waves are nearly horizontal, spiralling up the vessel wall (both interior and exterior). The final morphological trait in this combination is rilling, the tiny striations of raised clay formed by the passage of fingers, sponge or tool over the vessel surface during rotational shaping. These stria parallel one another, and are rarely more than 1 millimetre apart.

2) Torsional rippling is more likely visible through this formation technique than in method 1. The morphology of torsional strain and rippling, when viewed on a single face of the vessel (wall interior or exterior) is somewhat similar to the method 1 diagnostic trait of diagonally-oriented thickness discontinuities. What differentiates this method 2-specific trace is the fact that, if the interior face presents a diagonally-oriented concave band, the exterior face will present a corresponding convex band (method 1 vessels present a convex profile on both faces). In some cases, particularly smaller vessels, the walls appear to be folded. In other vessels, the trace manifests as a polygonal effect to the lower wall when viewed in plan. This trace is caused by the excessive braking effect of hands or tools on the vessel body during rotation, resulting in the twisting deformation of the vessel wall. In examining the experimental type set, these traces were particularly ephemeral on the larger vessels. These larger vessels were far more likely to tear from torsion during the potting process due to their dimensions, and as such were not fired. It is suggested here that more experienced potters would be able to successfully prevent torsional strain in larger vessels becoming so severe that they could not complete their vessels.

3) Although not unique to method 2 vessels, the appearance of re-smoothed vertical fissures differs slightly from the traces seen on method 1 vessels. In many cases, the vertical fissures are either arrayed in a horizontally oriented band, or branch from a similarly re-smoothed fissure with a horizontal orientation. A key observation in the method 2 vessels is that many of these traces occur in the vicinity of joined coils. The source of these fissures remains the same as in the case of method 1 vessels.

Figure 35A Carinated cup (vessel number 49) with generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling visible, especially above the carination.

Figure 35B. Straight-sided cup (vessel number 10) showing generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling, visible across the interior wall.

Figure 35C. Carinated bowl (vessel number 77) showing generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling on the interior wall.

Figure 35D. Rounded bowl (vessel number 61) showing generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling.

Figure 35E. Rounded jar (vessel number 106) showing generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling on the exterior wall.

Figure 35F. Basin (vessel number 82) showing generalised thickness discontinuities and vertical to diagonal finger impressions below convex/concave undulations along with fine to medium rilling.

Figure 36A. Straight-sided cup (vessel number 13) showing torsional strain/rippling, especially visible on the lower wall.

Figure 36B. Carinated cup (vessel number 50) showing torsional strain/rippling at the lowermost portion of the interior wall.

Figure 37A. Rounded cup (vessel number 32) with re-smoothed vertical fissures visible on the interior wall near the rim.

Figure 37B. Conical-based jar (vessel number 125) with re-smoothed vertical fissures visible on the interior wall.

Figure 37C. Rounded jar (vessel number 109) showing re-smoothed vertical fissures on the exterior wall, particularly at its widest point.

P1/4 The Method 3 Diagnostic Features

The presence of stacked, nearly horizontal coil seams in tandem with (but not precisely parallel to) rilling is another instance of several macroscopic traces appearing in conjunction to indicate forming method. The action of joining coils using rotation during the course of this experiment frequently prevented the obscuration of coil seams. These manifested as roughly horizontal linear traces which are trench-like in profile, caused by the close proximity of two concave bands. Over the course of rotational coil joining, wall thinning and shaping, these joins persisted and were overlain by almost-horizontal, spiralling rilling. These two types of macroscopic trace, though both nearly horizontal, differed in alignment in all observed cases and are therefore considered one of the most reliable indices of forming method identified by this experiment.

Figure 38A Straight-sided cup (vessel number 14) showing coil seams which do not parallel horizontal rilling on the interior vessel wall.

Figure 38B. Straight-sided cup (vessel number 17) showing coil seams which do not parallel horizontal rilling, visible on the interior lower wall/base.

Figure 38C. Rounded cup (vessel number 38) showing coil seams which do not parallel horizontal rilling on exterior wall surface, just below widest portion of body.

Figure 38D. Conical-based jar (vessel number 129) with coil seams which do not parallel horizontal rilling visible on the upper portion of the interior wall.

Figure 38E. Rounded jar (vessel number 114) with coil seams which do not parallel horizontal rilling seen on the interior wall surface.

Figure 38F. Basin (vessel number 96) with coil seams which do not parallel horizontal rilling visible on upper portion of exterior wall.

Bibliographie

JEFFRA, C. 2011. The Archaeological Study of Innovation: An Experimental Approach to the Pottery Wheel in Bronze Age Crete and Cyprus. PhD, Exeter: University of Exeter.ROUX, V. & M.A. COURTY. 1998. “Identification of wheel-fashioning methods: technological analysis of 4th-3rd millenium BC oriental ceramics,” Journal of Archaeological Science 25: 747–63.