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The production of a pottery bowl consists of a number of manufacturing techniques ranging from resource selection to the application of glazes. These stages are outlined within the Chaîne Opératoire, a term referring to the series in which a piece of pottery could be produced, used, destroyed and finally deposited; this essay will concentrate on the first of these stages outlined in Table 1 below (Rice 2005: 115, Knappet 2005: 678). Throughout the manufacturing of a pottery bowl a number of traces are left on any given vessel and these traces can be scientifically analysed to give evidence of these processes through macroscopic, microscopic or chemical techniques. This essay will endeavour to describe these techniques through the use of various examples in relation to their associated location within the Chaîne Opératoire.
Table 1: Principal stages in pottery manufacture
Source: Orton, Tyers & Vince 1993: 114 table 10.1
The first stage to be discussed is that of resource procurement and preparation; in these stages the raw materials used to create the bowl are extracted from the ground and refined by the potter (Knappet 2005: 678). The resources which are required include water, fuel, clay and if required non-plastic inclusions (Orton et al. 1993: 114, Sinopoli 1991: 9-10). This primary section however leaves little trace on the vessel itself due to its nature.
The preparation of the resources will often entail the addition of a temper or the removal of impurities by hand or through flotation (Sinopoli 1991: 16-17, Orton et al. 1993: 114). Temper within clay is usually a non-plastic material which makes the clay easier to work and is also used to prevent the breakage of the vessel during firing (Knappet 2005: 678). These additional materials can often be seen through macroscopic or microscopic techniques (Knappet 2005: 678). Early Prehistoric pottery assemblages within South Eastern Britain for example often contain non-plastic materials such as flint or crushed shells (Varndell & Freestone 1997 33-4, Cleal 1995). These materials therefore leave evidence of clay refinement within the finished product, which are often visible macroscopically through colour difference or raised areas (Varndell & Freestone 1997: 34).
The temper added to particular assemblages can also be utilised to identify the area in which the material was extracted. Peter Day's work on ceramics from Bronze Age Crete is one example of such a method where microscopic and macroscopic methods were used to identify tempers and their associated sources Knappet 2005: 680, Day 1999: 1029-30). It is argued that the temper originated from a riverine environment as opposed to the previously thought marine (Knappet 2005 citing Myer & Betancourt 1990). This is due to the sand within the vessels being of a single geological type rather than the mix that occurs within the local beach sand (Wilson & Day 1994: 52, Day et al. 1999).
The techniques mentioned above are however not completely indicative of temper addition, as it is possible for tempering to occur naturally within some clay deposits (Knappet 2005: 678), there are however quantitative techniques available which take the mineralogy of the vessel into account (Knappet 2005: 680-2). Whitbread for example utilises this technique to determine the modality of grain size of Greek transport amphorae by sampling distribution in a thin section (Knappet 2005: 680 citing Whitbread 1995). The frequency of the results are then used to interpret the clay as unimodal or bimodal. If the results are unimodal; the vessel was created utilising a naturally occurring source of clay with no evidence of human alteration (Knappet 2005: 680 citing Whitbread 1995: 389). If the results suggest a bimodal mineralogy however the matrix has been altered by man through the addition of a temper. This reduces the effect of the temper on the identification of the clay source itself. Whitbread himself utilised this technique to prove that particular Greek amphorae, such as Chian Fabric class 1 and Mendean amphora Fabric class 1 had been tempered by deliberate human action (Whitbread 1995: 349).
The clay source can also often be identified from the finished product through the use of Neutron Activation Analysis (NAA). This is a technique used to obtain a chemical profile of ancient pottery and this information can be used to determine a vessels provenance (Perlmon 1984: 117-119). Perlmon for example utilised this technique on Eastern Terra Sigillata found in Israel and discovered two major sources for the pottery sample selected, indentified by their relative differences in terms of chemical composition (Perlmon 1984: 128-32). The results shown in table 2 suggest this difference, particularly with the elements of Lanthanum (La) and Thorium (Th).
Table 2: Eastern Terra Sigillata
Cypriot pottery (18 samples)
Source: Perlmon 1984: 130 table IV
There are however some pottery assemblages which appear to have had impurities removed. The method involves the use of water to suspend the lighter clay particles above those of the impurities, often known as levigation and leaves a similar make up to that of a unimodal sample when analysed, inferring that the removal of impurities is not traceable (Sinopoli 1991: 16).
The next stage mentioned in table 1 is the shaping of the raw materials into its final form (Knappet 2005: 684, Shepard 1980: 54-55). This occurs in a number of ways which can be divided into two main methods; that of hand forming and wheel throwing as shown in table 3. These techniques are however not always used alone, as evidence on certain ceramic assemblages have two or more of the forming methods on single vessels. The pottery created by the Papago peoples of Southern Arizona for example is a modern ethnographical study where multiple forming methods were utilised on a single vessel (Rice 2005: 141). The majority of the vessels formed by this group use a combination of coiling, paddling and convex moulding (Fontana et al. 1962: 52-70).
Table 3: Forming techniques of pottery
These forming methods are indentified in a number of ways, primarily through the striations located on the vessel which can be viewed either macroscopically or through use of a Scanning Electron Microscope (SEM). Striations follow a particular patterning caused by the application of pressure upon the vessel during this stage (Rice 2005 citing Rye 1981: 59-81). The coiling technique for example leaves behind circular or near circular striations on the inner surface of the vessel due to the way in which the vessel is created (Rice 2005: 127). The pottery is formed using a number of coils which are then built up and smoothed over at the adjoining sections of the clay due to their likeliness of fracturing throughout later process (Rice 2005: 127-128). The striations shown in figure 1 (overleaf) are however often destroyed by secondary techniques such as through the paddling technique (Rice 2005: 137 citing Solheim 1954). This is where the partially formed vessel is repeatedly beaten either with or without opposing pressure (Rice 2005: 137). This method of secondary forming leaves a series of impressions on the interior of the vessel and also improves bonding between segments (Rice 2005 citing Scheans 1977: 13, 50)). The paddling technique appears to be associated with coil built pottery; but in some areas such as Pakistan the technique is used on wheel-thrown jars to enlarge the body of the vessel (Rice 2005: 137). Figure 1 illustrates these and other techniques and their associated striations (overleaf).
A Scanning Electron Microscope is used to illustrate these striations as structural changes within the fabric which have often been smoothed over by the potter prior to drying and firing (Rice 2005: 401-402). The instrument itself works through the firing of electrons at the sample and creating an image of its internal structure through the changes in energy recorded by the device (Rice 2005: 401)
Figure 1: diagram showing forming striations Source: Berg 2008: fig. 1
The fourth stage in the Chaîne Opératoire is that of pre-firing techniques, which are often macroscopically visible on the surface of the finished vessel (Knappet 2005: 687). The majority of these techniques are applied to wet clay due to the nature of the enhancement and many of these treatments appear to be have a mainly aesthetic purpose. One exception however occurs on utilitarian vessels such as cooking pots where the inner surface is roughened to improve heat transfer during the cooking process (Rice 2005: 138). This method of treatment is macroscopically visible on the interior leaving large evidence of this process on the finished product (Rice 2005: 232).
The outer surface of a vessel also changes during this process leaving decoration such as slips, glazes and surface displacement for the archaeologist to examine (Rice 2005: 147 ). The primary procedure applied to the majority of pottery vessels is that of smoothing or texturing the outer surface by hand or through the use of tools (Rice 2005: 138). Smoothing in particular can be differentiated from other methods based on the finish of the vessel; a vessel smoothed by hand for instance will leave fine striations and a matte type finish; as the particles are not aligned as when burnished by a tool which leaves a surface lustre (Rice 2005: 138).
The remaining methods of surface enhancement can be divided into two main categories; firstly enhancements that move or remove clay and secondly those that add additional materials on or to the surface of the vessel itself (Rice 2005: 146). The first of these techniques includes decoration such as stamping or incising (Rice 2005: 146). This leaves very little trace on the material in chemical terms but the decoration can be analysed itself in terms of its style and the context in which it was produced (Rice 2005: 248-9). Scientific analysis can however be done through microscopic scrutiny of the enhancements themselves. Incising techniques used on pottery for example can be examined in this way to tell which type of tool was utilised in the formation of raised areas, and the angle at which the incision is made (Shepard 1980: 198-202). A number of possible techniques used to incise a vessel are shown in figure 2 (overleaf).
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Figure 2: Incising techniques Source: Shepard 1980: Fig. 15
Glazes and slips are much more interesting in terms of their scientific analysis and related techniques, leaving a number of options for analysis. Paints and slips for example can be examined through the use of X-ray diffraction and Proton Induced X-ray Emissions (Knappet 2005: 688). These and other techniques were utilised on the Kamares Ware of Crete, which utilised both slips and paint on their Middle Bronze Age pottery (Knappet 2005 citing Noll 1978). The results of the study suggest that the two slips of red and black were composed of two differing forms of iron; haematite and magnetite respectively, whereas the white paint is composed of Calcium Silicate (Knappet 2005 citing Faber et al. 2002). This investigation however also utilised SEM due to determine how the slips themselves worked during the firing process as the red is created through oxidation, whilst the black is produced through reduction (Knappet 2005 citing Faber et al. 2002); these firing techniques will be discussed below within relation to the Chaîne Opératoire.
The next stage of the manufacture of a vessel is that of the drying process (table 1 above), this process leaves no trace in relation to the finished product as no chemical or physical changes are made to the vessel (Rice 2005: 152). The process is however necessary to prevent the vessel from fracturing during the next stage, that of firing.
This process involves the placing of the pottery upon a source of heat through either a kiln or open fire and allowing the pottery to chemically bond within. This creates the final product unless post-firing treatments are applied to enhance the product. This stage in the Chaîne Opératoire is particularly important as if problems occur the vessel is often unusable (Rice 2005: 152-3). The traces left on the finished vessel are those of colouration of the original pottery as well as that of any slip or glaze applied and this colour can be utilised to estimate the firing temperatures of that particular piece of pottery and whether the fire caused oxidation or reduction of any iron oxides within the source (Shepard 1980: 103). Pottery shows the greatest colour difference in terms of oxidation between 700-900ËšC, as the colour differences are more pronounced (Shepard 1980: 103). The Kamamres wares of Crete for example appear to have undergone a number of firings to create both the black and red colourations (Shepard 1980: 104).
The hardness of the finished vessel can also be examined to determine the firing temperature, but by combining the techniques one can examine the changes in hardness and colour throughout the vessel, inferring the level of control over the temperature and atmosphere during the firing process (Knappt 2005: 690-2). These methods must however be combined with chemical analysis techniques as the colouration and oxidation levels of any given pottery source varies according to the minerals within the clay paste prior to firing (Knappet 2005: 690-2).
The final process of the Chaîne Opératoire is that of post firing treatments; these are additional measures applied to pottery in order to improve the vessel by reducing its permeability or improving its overall appearance (Rice 2005: 163). These treatments are often organic in nature, particularly in relation to modern ethnographic examples (Rice 2005: 163). The potters in West Africa for example apply liquid mixed with pods of the locust trees to seal the pores of the pottery and to coat the surface (Nicklin 1981: 177)
In conclusion there are many traces left on pottery for the archaeologist to examine, both chemically and macroscopically. The traces are difficult to detect particularly in relation to vessels that have been used for particular functions as constant heating and reheating for example can recolour a vessel reducing its traces in terms of firing temperature. The potential manufacturing stages are also only part of the vessels actual Chaîne Opératoire as processes such as deposition and use wear must also be taken into account.