Experimental protocols
Previous work by the author (Jeffra 2015) focused on the demarcation of specific wheel coiling methods as laid out by Roux and Courty (1998), and this work was designed to be complementary. The present experiment differs from the previous one in several aspects. Firstly, distinct coil attachment gestures were used for the wheel coiling technique within this experiment, creating a new set of data to compare against earlier data. A single wheel coiling method was selected for comparison against wheel throwing in order to create an easily comparable dataset based on the same variables. Method 3 was selected for this purpose following its frequent identification with archaeological material in previous studies by the author, though it must be said that this frequent successful identification may be due to the single analytical method (naked eye observation of macroscopic surface traces) and other wheel coiling methods may have gone unrecognized in earlier research (Jeffra 2011, 2013) – indeed the author hopes that future research will prioritize multiple-technique assessment of material to successfully clarify production processes of objects with subtler surface traces.
A second important difference between this and the previous experiment is this experiment’s consideration of the impact of temper on the nature of trace evidence; examples of each vessel were formed using untempered as well as tempered clay. Two commercially available clays were used, selected for their ready availability to others who may wish to replicate this experiment, as well as to ensure consistency of raw material throughout the duration of the experiment. Furthermore, in the interest of maintaining general applicability of this experiment to multiple archaeological contexts, it was not the aim to replicate context-specific clay recipes.
Thirdly, reporting on this experiment provides another opportunity to include discussion of a significant omission from the author’s previous publications on the matter: the specific gestures used for the wheel throwing technique. There is a growing body of scholarly work investigating and reporting on the relationships between potting gestures, skill transmission, and production evidence, and it would be remiss to neglect this aspect of description. As such, the gestures are described in detail below, and can be further supplemented with open-access video recordings of each experimental vessel’s production, available online (https://tracingthewheel.eu). For precision, anatomical terminology is used to describe hand gestures, with relevant terms illustrated in Figure 1.
Lastly, the shapes created for this experiment were not selected solely with specific ceramic traditions in mind. Instead, the experimental type set was produced to adhere to the principle of a generalized type set, as described in Jeffra (2021). The type set was formulated as a foundation for comparison, a starting point from which successful technological assessments can be made in the first instance as well as a means for future experiments to readily direct resources toward more specific questions.
As in the previous experiment, vessel surfaces were left entirely unaltered. The tools were the same: an electric potter’s wheel (Shimpo Whisper-T, operated in a counterclockwise direction), the potter’s hands, a sponge for applying/removing water and finishing the rim, and a wire to cut vessels from the wheel surface. As before, these practices were selected to prevent the appearance of macroscopic traces from tools not verified archaeologically.
An electric kiln with a programmable controller was used for firing vessels, and five separate firings took place during 2018-2021. The firing program consisted of three segments: segment 1 ramped 80 degrees C per hour until reaching 345 C, segment 2 ramped 125 degrees C per hour until reaching 595 C, and segment 3 ramped 150 degrees C per hour until reaching 1050 C. The observed temperatures, as displayed by the kiln thermocouple and digital display, deviated slightly from this program, but the curves overall followed the program very closely, as shown in Figure 2.
The specific process of forming the experimental vessels varied depending upon the technique employed, so it is necessary to discuss each in turn. It should also be noted that this experiment was completed by the author. She is a non-specialized, at most part-time, well skilled potter, who has sporadically practiced pottery production by hand for 25 years and the potter’s wheel for 15 years. In this time, she has also used a variety of wheel configurations, both powered and manual, and has completed several experimental programs of a comparable scale to the one reported here.
Method 3 ‘wedged coil’
Method 3 of the wheel coil technique, as defined by Roux and Courty (1998), is characterized by the use of discontinuous pressures only to form coils, and joining and thinning of those coils as well as shaping the roughout is achieved with the use of RKE. The supposition is that the continuous pressures from using RKE through so much of the overall process will strongly deform coils and wall surfaces, ultimately obscuring most 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. The forming process was consistent across all vessel shapes formed, as well as between the two clay types used. The base of each vessel is created by taking a small mass of clay and compressing it first into a sphere. Pressure is then applied to two opposing poles of the sphere using the forefinger and the thumb of one hand while the other hand supports the sphere along an equatorial line. The mass of clay is then rotated around its poles with the application of discontinuous, pinching pressure. These gestures quickly create a lentoid shape, which is then placed in the center of the wheel head. Coils are formed by holding a small mass of clay vertically between the two palms and applying rolling pressure bilaterally, to allow a 1.5-2cm coil to extrude downward toward the work surface. The so-called ‘wedged coil’ method of coil building was adapted to wheel coiling for this experiment. ‘Wedged coil’ describes a method of building up wall height by applying coils to the inner surface of the existing wall height with a rolling motion to integrate the mass of the coil into the mass of the wall and distribute that collected mass upward, thus raising the overall wall height. After this application of the coil to raise the wall height, the inner wall surfaces readily show numerous linear crevices from incomplete joining of coil mass to wall mass whereas the outer walls do not; the coils are, after all, applied to the inner surfaces and unless the mass of the wall is pierced in some way during that application, it will only be stretched. If using wedged coiling alone to create a preform, at this stage the potter would fully smooth the traces left on the inner surfaces before thinning and shaping the wall. Alternatively, the thinning and shaping actions might take place after each coil is applied, after several coils are applied, or even once all coils are complete. For wheel coiling within this experiment, the coils were stacked in a clockwise direction in the fashion described above for each vessel before continuous pressures were applied to them using RKE.
Using an electric wheel, coils were fully joined, and the vessels were thinned and shaped. Once all coils are stacked, rotation is started in a counterclockwise direction. The first action is securing the vessel base fully to the wheel head. With dry hands, gentle continuous pressure is applied to the center of the inside of the base with the fingertips. By moving the pressure application from center toward the vessel wall, it is possible flatten the shape of the inner base and prevent trapping extra air between vessel base and wheel head. Once the application of pressure reaches the inside corner where base meets wall, pressure is applied with the potter’s other hand to the outside of the vessel where the vessel walls come into contact with the wheel head. This creates a closer seal with the wheel head and prevent the ingress of water during later stages of thinning and shaping, which would create a weak point where the vessel could come away from the wheel head.
After fully securing the vessel to the wheel head, water is applied to inner and outer surfaces alike using a small sponge. In this application of water, the sponge and the potter’s hands are held in very light contact with the surfaces to aid in forming a thin layer of slip. The pressure applied is gentle enough to ensure contact but not so strong as to risk any deformation. This thin layer of slip creates better lubrication of the surfaces than water alone. With the surfaces wetted in this way, the walls are thinned and shaped using bilateral pressure applied to the walls in two separate episodes – firstly from top to bottom and then from bottom to top. Working from top to bottom, the hands are interlinked at the thumb and second and third digits of each hand are used to create pinching pressure starting at the rim. This gesture of joined hands to pinch the walls is held steady and moved down the full height of the walls with the effect of largely eradicating perceptible (by touch) coil join crevices. By and large, this ‘first pass’ from rim to base does very little to determine the final shape of the vessel, but rather serves to redistribute wall mass more symmetrically and complete the joining of the coils.
The ‘second pass’ of continuous pressure application uses a similar gesture – hands interlinked at the thumbs and second and third digits of each hand acting as pincers – this time starting at the lowermost point of the vessel wall and working upwards. In this case, pressure is applied to redistribute wall mass upward and according to the desired final shape. In shaping, this means that extra pressure applied using the fingers on the inner wall will force the wall outward (making the vessel diameter larger), while consistent pressure between both inner and outer wall fingers will force the wall to become taller (making the vessel height greater). For this experiment, in no case was it necessary to constrict the diameter of the vessels being formed, but it should be noted that this constriction action would have necessitated different, specialized gestures. The bottom-to-top pressure action is repeated multiple times, with less and less pressure needed each time as the vessel becomes thinner and closer to completion.
Once the desired shape and wall thickness is reached, the rim is tidied by bracing either side (inner and outer) of the upper wall using a thumb and forefinger of one hand, and slight downward pressure would be applied using the forefinger of the opposite hand. Any final excess water pooling in the interior base is retrieved using a sponge at this point. The rotation of the wheel head is then stopped, and the base is cut from the wheel head using a twisted wire.
Wheel Throwing
The wheel throwing technique is characterized by the use of a use of a potter’s wheel to rapidly rotate a mass of clay, and using the rotational inertia of that rotation to manipulate that mass and draw it up and/or out into the desired vessel shape. Wheel thrown vessels can be thrown off the hump – that is, a single mass is used to produce multiple vessels in succession – or they can be thrown singly. In this experiment, vessels were thrown one by one rather than off the hump. Within the operating procedures of this forming technique, specific actions were undertaken, corresponding with specific gestures, for the production of all wheel thrown vessels, though there was some variation in the application of those gestures (as well as supplementary actions/gestures depending on the desired final vessel form).
The wheel throwing technique undertaken by the author is divisible into six operating procedures: freehand wedging and placement on wheel head, rotational wedging and centering, opening the volume, establishing the walls, thinning and shaping, and removing from wheel head. Each of these operational procedures can be understood in terms of their aims and a description of accompanying gestures. The gestures are described here in detail to supplement the video recordings of the potting process. It should be noted that aside from the first and final operating procedures (freehand wedging and placement on wheel head, and removing from wheel head), all operating procedures are completed with rapid rotation of the wheel and the repeated, liberal application of water to the clay surface. Once the volume is opened to create an interior, this applied water can gather there and must be removed periodically with a sponge or cloth.
Freehand wedging and placement on wheel head
Freehand wedging is a transitional operation bridging between paste preparation and wheel throwing, when the desired amount of clay for wheel throwing is removed from the larger mass of prepared clay. This smaller amount represents the total quantity of clay required for producing a single vessel (in the case of throwing vessels one by one), which is attached to the wheel head securely with a minimum of trapped air so that adhesion can be maintained throughout the remainder of the wheel throwing process. Freehand wedging re-homogenizes the mass of clay for throwing with percussive force, compressing the mass to drive trapped air out.
The clay is cupped in one hand and is struck by the opposite hand in a clapping motion, which is also held in a relaxed cupping position. Rather than a clapping motion where hands meet palm to palm, the hands instead meet with 45’ rotation, and the heel of the hand is used to strike (see Figure 3). After each strike, the mass of clay is rotated slightly so that successive strikes reach different areas. Through this constant rotation, the mass is homogenized and formed into a roughly spherical shape. Larger masses of clay for larger vessels are instead formed into a rough ovoid shape. In either case, the mass is roughly shaped in order to present a regular convex surface when attaching the mass to the wheel head. In this way, the risk of trapping air between clay mass and wheel head is minimized; if air were to become trapped in this way then it would present a greater risk for the clay mass to pull away from the wheel head during potting, resulting in vessel failure.
Placement on the wheel head is completed by gently throwing the mass of clay down onto the surface of the wheel head so that it strikes as close to the center as possible. In the present experiment, if the clay mass landed off center then it was possible to gently slide the clay to the correct position without losing adhesion. This was done by applying firm and gentle pressure to the far side of the clay using the palms of both hands and pulling it toward the potter’s body. These repositioning actions were not attempted for distances of more than 3-4 cm.
Rotational wedging and centering
Once affixed to the wheel, the mass of clay can be rotationally wedged and centered completely. The aim of this operating procedure is to force out any remaining trapped air from the clay mass, to ‘warm up’ the clay and make it more workable for subsequent actions, and to ensure that the mass is properly centered and symmetrical. The gestures for this procedure are performed to alternate between bilateral pressure (to more or less triple the height of the mass while narrowing its footprint by one third to one half, forming an elongated, truncated cone) and combined downward and lateral pressure (to reduce the overall height and widen the footprint, forming a low and wide cylinder). The alternation between these two shapes – elongated truncated cone and low wide cylinder – has the effect of repeatedly distributing clay mass upwards and back down again. The rotation of the wheel head in conjunction with these actions forces the mass of clay to become symmetrical and centered on the wheel head.
In order to raise the mass of clay into a truncated cone, water is first applied to the surface of the clay. The slip formed on the surface acts as a lubricant to allow the mass of clay to be molded using the pressures of the hand gestures rather than the friction that those pressures create. The left hand is placed so that the fifth digit and ulnar border of the hand rest lightly on the wheel head and the mass of clay is in contact with the palm (Figure 4). The hand is bent at the metacarpophalangeal joints with the fingers otherwise straight but relaxed. The right hand is in contact with the left hand during this gesture, with the thenar eminence of the right hand resting on the carpometacarpal joint of the left thumb. The right thumb is looped over the left wrist, resting on the back of the left hand, and the left fingers are in contact with the mass of clay from the metacarpophalangeal joints to the fingertips. This contact directly between the hands, common in many of the gestures described throughout this process, is maintained wherever possible so that the potter can better control and coordinate the spatial relationship between the two hands; this contact is not just about increasing stability or strength but also serves the important function of providing feedback signaling as well.
The bilateral pressure exerted on the mass of clay comes from contact by the thenar eminence of the left hand (supported by the thumb of the right hand in its position) and the palmar surfaces of the fingers of the right hand. The hands apply pressure to the mass of clay at the lowest point, closest to the wheel head, and the hands together are raised to exert pressure higher on the mass as the truncated cone grows taller.
Once the truncated cone is established, the next gestures serve to deform the mass of clay into a low and wide cylinder. The left hand is placed atop the clay mass so that the peak is in contact with the thenar eminence (Figure 5). As before, the left hand thenar eminence is supported by the thumb of the right hand. The fingers of the right hand are bent at the metacarpophalangeal joints with their palmar surfaces in contact with the mass of clay at its side. The left hand fingers are bent at the metacarpophalangeal joints and rest atop the right hand fingers for support. This gesture is used to apply even, downward pressure to the clay mass led by the thenar eminence of the left hand. The palmar surfaces of the right hand’s fingers act to hold the sides of the mass steady, forcing the mass to expand outward uniformly as the height is reduced. The hands are held in this gesture and moved downward as a unit.
Once the clay mass is appropriately reduced in height, the top is flattened. This is done using downward pressure from the ulnar border of the right hand’s fourth digit. The right hand is held so that the third and fourth digits are bent at the metacarpophalangeal joint and the interphalangeal joint of the thumb is resting on the radial border of the third digit’s proximal interphalangeal joint. The second and the fifth digits of the right hand are relaxed but held straight and out of the way. The left hand thumb’s interphalangeal joint rests near the right hand’s thumb atop the right hand’s radial border of its third digit’s distal interphalangeal joint. It is in this way that both thumbs reinforce the strength of the third and fourth digits of the right hand as downward pressure is applied to the top of the clay mass, creating a level surface prior to the next operating procedure.
Opening the volume
The aim of the operating procedure “opening the volume” is to create a well centered void of an appropriate depth within the mass of clay so that the vessel base is the desired thickness and diameter, and clay mass is distributed appropriately to form symmetrical walls. To do this, it is first necessary to create a small hole in the centered mass. This hole is then widened and the inner base surface is evened and compressed.
Centering the aperture on the clay mass requires the application of pressure to a point very slightly offset from the center of rotation. By offsetting the point of pressure, the potter must hold their finger in tension as they pull the mass of clay very slightly outward and press down. In this way, the clay is forced to move around a finger held in tension, and a void which is slightly wider than the finger is created. Both hands are placed so that their radial borders are in light contact with the wheel head and the hypothenar eminences through the length of the fifth digits are in light contact with the lowermost portion of the mass of clay (Figure 6). The right thumb is bent at its interphalangeal joint so that its tip is oriented more or less perpendicular to the wheel head. The left thumb rests on the dorsal surface of the right thumb’s interphalangeal joint. The two thumbs apply downward pressure, flexing at their metacarpophalangeal joints, until they nearly reach the wheel head. The placement of hands in contact with the wheel head alongside the clay mass is an important aspect, as they provide feedback to the potter about the depth of the void as it is created, which effectively establishes the thickness of the vessel base.
Once the full depth of the void is created (and therefore the thickness of the base), the aperture must be widened. This action sets the approximate dimensions of the base diameter and prepares for subsequent actions to establish, shape, and thin the walls. The gestures for this are completed with a steady lateral, pulling motion where pressure is applied to the mass of clay from the inner side closest to the potter’s body and pulled further. This pulling action, combined with the rotation of the wheel, drives the clay outward and symmetrically opens the aperture to the needed dimensions.
The right hand is held so that the third and fourth digits are bent at the metacarpophalangeal joint and making contact with the inner surface of the clay mass closest to the potter’s body. The tip of the thumb rests on the outer surface of the clay mass closest to the potter’s body. The second and the fifth digits of the right hand are relaxed but held straight and out of the way. The left hand supports and strengthens the position of the right hand. The second and third digits rest on the dorsal surface of the right hand’s third and fourth digits, between the proximal and distal interphalangeal joints. The thumb of the left hand rests on the dorsal surface of the right thumb’s metacarpophalangeal joint (Figure 7). In effect, the portion of the clay mass closest to the potter’s body is pinched between the fingertips and the thumb of the right hand. The left hand reinforces the pressure of pulling the right fingers toward the right thumb while keeping the thumb stationary. As this pinching movement is performed, the fingers of the right hand are curled by flexing the distal and proximal interphalangeal joints. This curling action is controlled and slow so that the fingers can move levelly without gouging into the base (to create thin areas) or lifting (to create thicker areas).
Establishing the walls
The previous gesture of widening the aperture creates a volume which can be described as a torus of wall mass sitting atop the disc of the base. The aim of establishing the walls is to transform the torus-shaped mass of clay sitting atop the roughed out base into roughed out walls. This operating procedure therefore realigns the placement of that torus with the dimensions of the base before altering its morphology so that it is more readily thinned and shaped in the subsequent operating procedure.
Prior to the first gesture of this operating procedure, the disc diameter corresponds to the inner diameter of the torus (see Figure 8). The first gesture used for this operating procedure is performed to fold the walls in. Folding the walls in reduces the torus in size so that instead, its major diameter matches that of the base disc, reestablishing the diameter of the base as the starting point from which the walls of the vessel will rise.
The hands are placed so that their radial borders rest on the surface of the wheel, and the palms from hypothenar eminence through proximal interphalangeal digital creases are in contact with the clay where it meets the head of the wheel. The hands are positioned so that the hands are at a 45’ angle to the wheel head, palms facing upward and near-contact between the carpometacarpal joint of the fifth digit. This position has the effect of cupping the torus along the palms and when the hands are rotated slowly inward the pressure exerted has a rolling or folding effect. The torus is forced to constrict into a smaller diameter through this consistent but strong pressure.
Folding the walls in in this way does have the potential to redistribute clay mass asymmetrically across the torus. The walls are therefore evened up using a knuckle, which has greater potential for strength and stability despite somewhat less sensitivity than using fingertips.
The tip of the right thumb is touched to the middle interphalangeal digital crease of the right hand’s second digit, and that digit is wrapped around the thumb at the point of contact by bending the second digit at its proximal interphalangeal joint. The remaining digits of the right hand are flexed into a loose fist to tuck them out of the way. The thumb of the left hand is placed palmar surface to palmar surface with the right thumb, so that the left thumb is looped behind the second digit and right thumb configuration. The second and third digits of the left hand are loosely flexed, while the remaining fourth and fifth digits are flexed to tuck them out of the way. Pressure is applied to the exterior of the clay volume using the ulnar border of the flexed and supported second digit, while at the same time pressure is applied to the interior of the clay volume using the fingertips of the second and third digits of the left hand (see Figure 9). This gestural configuration is used to apply pressure first from the exterior where the clay mass meets the wheel head. Corresponding pressure is then applied from the interior wall where it meets the base. The locations of these applications of pressure are offset from one another due to the base thickness, which results in the presence of a sinuous curve. The hands are held in position relative to one another and moved up the vessel wall and slightly inward toward the axis of rotation. This upward movement of the hands forces the vessel wall to undulate through the pressure of the sinuous curve thereby homogenizing the wall thickness and morphology; clay in excess of the determined thickness established by the gesture is redistributed upward.
Thinning and shaping
The operational procedure of thinning and shaping transforms the walls established from the previous actions into the final morphology and dimensions desired of the vessel being created. Two gestures are completed to transform the vessel morphology and to finish the rim morphology, respectively. The first gesture of this procedure mirrors that of the final gesture of the previous procedure; a sinuous curve is formed in the lowermost portion of the vessel wall and this curve is drawn upwards to force the deformation of the wall. This approach is combined with lateral pressures to pull the wall diameter wider or else greater pinch pressure to draw the wall mass upwards to raise the height.
The gesture used for wall thinning and shaping acts to pinch the wall between the fingers of the right hand from the exterior and the fingers of the left hand on the interior. On the right hand, the thumbtip presses on the palmar surface of the distal interphalangeal joint on the third digit. The second digit is extended alongside the third digit and kept in constant firm contact for strength and support. The fourth and fifth digits are flexed and tucked out of the way. The left hand third and fourth digits are held in a gentle flex position, with the second and the fifth digits held extended and lifted to be out of the way. The left thumb tip is placed atop the dorsal surface of the right hand on its thumb’s metacarpophalangeal joint (see Figure 10).
As before, this gestural configuration is used to apply pressure first from the exterior where the clay mass meets the wheel head. Corresponding pressure is then applied from the interior wall where it meets the base. The offset application of pressure again results in a sinuous curve. The hands are held in a fixed position relative to one another and moved up the vessel wall. This upward movement of the hands forces the vessel wall to undulate through the pressure of the sinuous curve to redistribute excess clay mass upward along the desired trajectory of the vessel wall’s curves. This gesture is repeated a number of times to transform the walls in stages. Each pass of this gesture from vessel base to rim is an incremental step morphologically from vessel roughout to vessel preform.
Once walls have been raised into the desired morphology the rim is often slightly asymmetrical or otherwise irregular. The gesture for tidying the rim applies pressure to either side of the upper wall (interior and exterior) as well as atop the rim to create a uniform rounded curve.
This gesture consists of the left hand second and third digits flexing at the metacarpophalangeal joints and being used in conjunction with the thumb of the same hand. The palmar surface of the second fingertip is applied to the uppermost area of the vessel wall interior. At the same time, the palmar surface of the left thumb tip is applied to the uppermost area of the vessel wall exterior. The remaining digits are held extended and out of the way. The right second and third digits are held so that they are in contact with the uppermost edge of the vessel rim, and touch the left hand at the distal interphalangeal joint of the second finger as well as the interphalangeal joint of the thumb (see Figure 11). The points of contact with the left hand – upper interior and exterior – are held steady with gentle support while the fingers of the right hand apply slightly stronger downward pressure. Once the rim profile has been transformed from an inverted ‘V’ (or similar) to an inverted ‘U’, the gesture is complete.
Removing from wheel head
The final operational procedure releases the completed vessel preform from its attachment to the wheel head for drying, further finishing actions, and later firing. Excess water and slip are removed from the exterior surface and interior base of the vessel with rotation. Within this experiment, the rotation of the wheel is stopped at this point and a thin, twisted flexible wire is used to cut through the base where it is attached to the wheel head. The hands are spaced so that they are wider than the diameter of the vessel to be cut from the wheel. The wire is held taut between both hands and then gripped so that it is pressed against the wheel head with each thumb. While pressing down against the wheel surface and keeping the wire in tension, the hands slide along the wheel surface to force the wire underneath the vessel and across the wheel surface, completing the cut. Following this, the wire is set aside and the vessel is carefully lifted with both hands from the wheel surface.
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