8 Understanding Material Culture Remains : Ceramic Technology

Ravi Korisettar

Introduction

Man has experimented with the soft, plastic earthy material as medium of decoration or expression since hundreds of thousands years ago. However, recorded usage of clay in potting varies between eight to ten thousand years in different parts of the world. Pottery was the first synthetic material that was created by man. Pottery is a part of, although a large one, ceramic technology. The term ceramic is derived from the Greek word keramos which means “burned material” or “earthenware”. While the term ceramic is used to refer to high-fired, glazed, vitrified tableware, art objects and structural clay products; the term pottery is used to refer to low-fired, unvitrified objects and/or cooking and storage vessels. It is this bulk of low-fired, unvitrified pottery that is of concern to prehistoric archaeologists and anthropologists.

The beginnings of the use of clay by man can be traced back to its uses as decorating the bodies with coloured clays. Clay was also used in artistic expressions on clay walls, floors and figurines in Upper Palaeolithic Europe. It was the application of pyrotechnology to manipulate and transform soft clay to hard and durable pottery that made it survive through millennia in the archaeological records. It is also certain that pottery like many other milestones such as lithic technology, agriculture and settled communities, has developed independently in several centres. Multiple causes and scenarios have been proposed to explain the origins of pottery. It is interesting to note that the earliest forms resemble earlier containers of naturally occurring materials like gourds, wicker baskets, leather bags and hollowed-out bamboo bottles. This perhaps is due to the use of clay to line, mend or reinforce the natural containers. In aceramic Neolithic levels of Jarmo and Jericho, clay lined pits and baked-in-place ovens have been identified. Another argument is that sun-dried hardened clay containers precede fired pottery in many cultures. Thus, it can safely be concluded that pottery technology owes its origins to experimentation and practical experience.

The emergence and increased appearance of pottery is associated with the Neolithic culture, a technocomplex of tools of food production and containers of food preparation and storage. This is a marker of changes in economy in the Holocene period primarily food collection to food production and the shift towards sedentary lifestyle (Arnold, 1985). It also indicates the necessity to process and prepare the domesticated grains that had gained prominence in Neolithic diet. Interestingly, one of the theories states the necessity to detoxify plant foods by heating as the cause of origin of pottery (Arnold, 1985).

2. Pottery as Archaeological Evidence

Pottery found in archaeological record has been used for specific purposes by particular people or in a particular place at a specific time. Analyses of pottery assemblages found in archaeological record answer questions relating to chronology, dating, exchange, migration, functionality and technology to list a few. Let us briefly examine its role in the above.

Pottery – forms, wares, techniques – exhibits a good deal of variation in a site/region. Not only does it help in relative dating of a culture, the pottery assemblages also betray a developmental trend. Change in pottery types reflects the continuous cultural change. A typological study of pottery found in many sites aids in seriation and regional spatial distributions. It also plays a crucial role in cross-dating or transferring of absolute dates from one site to be applied to other sites with similar cultural remains.

Shepard’s (1956) work was a turning point in ceramic studies as she integrated typological studies to understand chronology and distribution with technological studies based on identification of materials, characteristics of different forms and exchange. The technological studies of pottery provide insights into clay selection, potter’s skill, and control over firing conditions.

Another interesting potential of pottery studies is in the field of understanding cultural exchange, interactions and migrations. The occurrence of similar pottery types and specific forms in the cultural sequence across multiple archaeological sites of a specific region or across different micro cultures suggests possible interaction of authors of the culture. Sometimes potters attempt to replicate a distinctive ware of the same or another culture as a result of interaction and influence. A technological investigation involving the study of inclusions in the clay paste can throw more light on the provenance and also plausible exchange network or migration of people. It is interesting to note that exchange or movement is not limited to the luxury ware or tableware. A provenance study on relatively humble coarse wares can establish association with exchange networks. From simple scientific techniques like thin-section analysis to more advanced techniques to understand the composition of the clay used like XRD (X-Ray Diffraction Spectroscopy),XRF (X-Ray Flourescence Spectroscopy), NAA (Neutron Activation Analysis), OES (Optical Emission Spectroscopy), AAS (Atomic Absorption Spectroscopy) and ICP (Inductively-Coupled Plasma Emission Spectroscopy) have been employed to understand the clay composition, inclusion, trace elements and firing environments. Hence, questions related to provenance as well as those pertaining technology employed by ancient potters are well answered by these scientific probes.

Ceramics are essentially tools, which are used in processing, storing and transporting food, of many kinds. The wide range of pottery in the assemblages indicates to the various functions. The taxonomy of pottery forms is at times unclear and overlapping, thus hampering the understanding of their functionality. Here, it is noteworthy that it is not uncommon for a vessel to be used for different purposes. However, the design and engineering of these tools should render them most suitable for their intended use. Apart from the functions mentioned above, many variables combine to determine the morphology of pots. These are state of matter of contents, nature of these contents, and frequency of use, duration of use, distance involved in transportation and also the application of heat during food processing. Morphological classification is drawn considering the relative proportion of the different parts of the vessel like rim, orifice, neck, body and base. In turn, the functions these vessels perhaps performed are inferred. The knowledge of function of these vessels along with inputs from archaeo-botanical studies provides valuable insights into the diet and culinary traditions of the culture. The change in pottery forms indicates the emergence of new food practices. For instance, in the later phases of Southern Neolithic sites, channel spouts and perforated strainers emerge (Nagaraja Rao, 1971; Allchin, 1960; Subbarao, 1948; Wheeler, 1948).This suggest newer ways of preparing or storing food. Many uses were attributed to the later from being an incense burner, or strainer, to being used in steam cooking. Fuller (2005) associates it to curd straining activity. Noteworthy is the fact that specimens of restricted-neck jars have also been identified in Southern Neolithic . It is also important to note here that functionality determines not only morphology of the pots but also the technology that is employed in pottery manufacture.

3. History of ceramics

The earliest use of clay in the Near East has been associated with architectecture in sedentary agricultural communities. In these contexts it has discovered that clay mixed with chaff was used in constructing or plastering of walls, roofs and floor. Similar adobe bricks for used for constuction in the Zagros region as early as 7500 BC. Molded, sundried bricks continued to be used untill being replaced by fired bricks by 1500 BC.

Due to its impermanence, we have few archaeological evidences of unfired pottery. In the Near East, earliest pottery containers have been found in Çatalhöyük in Turkey dating back to latter part of 9th millennium BC. Earliest pottery containers from Syria and Zagros are have been dated back to latter part of 6th millennium and 8th millennium BC respectively. By 1500 BC, pottery manufacture had grown beyond providing household utensils to attain industrial proportions with the development of kilns, potter’s wheel, and application of glazes.

Archaeologically, earliest innovations in all stages of pottery production have been achieved in the Far East. However, due to the later technical and aesthetic advancements in the craft, the earliest “primitive” pottery did not receive much attention in archaeological research initially. The dating of the oldest Jōmon type of pottery with cord-impressed decoration from Japan is rather controversial. While radiocarbon dates from a few specimens go back to over 12000 BP, thermo luminescent dates ascribe mid-sixth millennium BC for the handmade, decorated Jōmon pottery. Mostly found types include jars with small bases. The earliest pottery from China from southeast coast also cord and shell marked and incised types have been dated to seventh millennium BC. The later Chinese pottery of the Yangshao culture of the Yellow River Valley from latter part of fifth millennium BC is handmade and decorated red and black geometric patterns. The Yangshao pottery fired in updraft kilns also have potter’s marks. It is suggested that the thick-walled dishes could have been made on a slow wheel although the fast wheel-turned pottery emerge in 1500 BC. The ceramic history of China is incomplete without the mention of the terracotta soldiers, technical achievements of high-fired pottery and glazes, stoneware, celadon and porcelain. However, these fall outside the ambit of the present discussion.

In Europe, pottery development is associated with emergence and development of agriculture and sedentary life in the Near East. European pottery is marked by high-fired Greek figured pottery of the sixth to fourth centuries BC and Roman Arretine Ware of the first century BC. Attempts to reproduce Greek figured pottery with fine glossy slip of illite and controlled kiln atmosphere had limited successes in the twelfth century onwards since the slip was mistaken for a glaze. The beautiful red lustrous bowls of Roman Arretine Ware were produced in multiple centres. In the medieval period, the tin-glazed Majorca pottery are important.

In the New World, as in the Old World, the emergence and development of pottery is associated with transition to farming and sedentary settlements although much later. Adobe bricks were used in the construction of ceremonial buildings in the Peruvian coast as early as 1900 -1800 BC.The absence of glazes, potter’s wheel and kilns in pre-Columbian period is noteworthy. Glazes, wheel-turned pottery and kilns were introduced by the European settlers. Although technical advancement and standardization could not be attained due to the absence of pottery wheel and kilns, painting and decoration on pottery from the New World betrays a high degree of technical skill. Pottery from Yucatán display certain features derived from the use of a rotatory movement or turntable. Wares with clay-rich slips, lead-coloured plumbate ware, and those with poly-chrome painting are prominent from the pre-Columbian period. Paintings of animal and human figures in graceful and natural style depict mythical and ritual scenes.

4. Ceramics in Indian Subcontinent

The earliest ceramics recovered from Period I B of Mehrgarh in Baluchistan are handmade, buff, chaff tempered and soft in texture. The simple forms of pottery from Mehrgarh share stiking similarities pottery from Iranian plateau. The technology of pottery production in Mehrgarh is traced back to its evolution from basketry. Pottery from the assemblage associated with Mehrgarh II A show clear signs of forming from slabbing, while those from Period II B indicate that the pottery was wheel turned and formed using paddle and anvil method. The more advanced wheel turned pottery occur in Period III of Mehrgarh. Harappan pottery traditions of the Early Harappan and Mature Harappan phases are listed in the following tables based on Krishnan (2014).

Table 1: Pottery types of Early Harappan Phase

It is noteworthy that in the Late Harappan Phase not only did the earlier pottery traditions continue but also many traditions that were indeed an amalgation like Bara Ware, Cemetry H, Ochre Coloured Pottery, Late Sorath Harappan, Savalda and Jorwe Ware emerged.

Within the Southern Neolithic complex, it is interesting the basic pottery types and forms viz., pale grey ware in simple forms like bowls continue from early Ashmound phase to the transition phase to Iron Age. However, as noticed by Allchin (1960) and studied thereafter by Fuller (2005), many forms emerge in the Neolithic. This change can be associated either with the adoption of new foodstuff or a change in food preparation techniques. There are many other forms which emerge earlier in the Southern Neolithic than in the Deccan Chalcolithic suggesting a northward spread. Lets discuss the interesting cases of the spouted jar and perforated pottery. The later dates of occurrence of the spouted jar along with channel spouted form in the Malwa-Jorwe horizon have been identified in earlier assemblages at Piklihal, Sanganakallu, Brahmagiri and other sites, thus indicating its spread from the South Deccan. The perforated pottery has been associated with diverse culinary functions including steam cooking, cheese making, preparation of “milk tubes”, brewing and covering functions. Alternatively, they have been identified as incense burners and braziers. The specimen from Watgal with perforations and spouted lip and another lipless rim from Balijapalle suggest regional variations in use. However, like the spouted form, these occur at later levels outside of the Southern Neolithic.

Pottery forms like the restricted neck jar and flat plates emerge in the Southern Neolithic only in the later levels. The restricted neck jars, generally associated with milking or water carrying functions, mark a range of liquid related activities in the culinary repertoire. Their occurrence alongside the introduction of wheat and barley may be seen as the introduction of fermented drink in the culinary of the Neolithic period. Similarly, forms such as flat plates which have been noticed in the Harappan pottery assemblages since 3000 BC and in the Jorwe period from 1500 BC, remain absent in the Southern Neolithic. It was only in the Iron Age c. 500 BC that flat forms emerge in this region. Archaeobotanical studies provide indisputable support to the above fact that newer forms in the pottery repertoire is associated with crop diffusion; northward spread of millets and southward spread of winter crops like wheat and barley.

5. Pottery Manufacturing Technology

Ceramics are composed of three basic raw materials: (a) clay, a sticky, fine-grained sediment that attains plasticity when wet or the property of being given shape by moulding when a limited amount of water is added; (b) non-plastic inclusions, mineral or organic inclusions found naturally in clays or deliberately added to alter the plasticity of the clay as desired and make it workable and also to limit shrinkage; and (c) water, added to the clays and inclusions to make them plastic and workable and that is lost during drying and firing. Other materials like slips, glazes and pigments are also used but for finishing the pottery. The other major raw material is the fuel used for firing.

The term clay is usually defined as fine-grained earthy material that becomes plastic or malleable when moistened. Clays are sedimentary deposits, products of weathering and disintegration of much older rocks. The deposition of clays in relation to the parent rock is one basis for classifying clays as either primary (also called residual) or secondary (also called transported or sedimentary) (Rice,1987). Primary or residual clays are those deposits which remain in the same location as the parent rock from which they have formed. They are formed due to a series of hydrolytic reactions involving percolation of water and resulting chemical action and also the other physical weathering processes.

Secondary or transported or sedimentary clays are found in deposits some distance from a probable parent source, transported by streams, rivers, glaciation, erosion and wind. Sedimentary clays are more common than the residual clays and are more homogenous as well as finer in texture, for they are well-sorted and redeposited by external agencies. In comparison with the residual clays they are comparatively higher in organic content. These naturally occurring clays were utilized by early potters in pottery manufacture (Arnold, 1985). Clay sediments occur throughout the world, although they vary considerably in their mineral content and quality as pottery-making raw materials. Variations in pottery making techniques and also forms of pottery should be viewed as having been influenced by the quality and nature of the raw materials (Sinopoli, 1991).

Clays can be defined on the basis of their chemical composition. Clays being the products of weathering of silicate rocks, are primarily composed of silica and alumina, the two chemical elements most resistant to weathering. Clays mostly comprise of a small number of elements and compounds, mainly silicates, alumina and water in crystalline structures, although other minerals like potassium, sodium, calcium and iron among others occur in smaller quantities (Rice, 1987).

Mineralogically, most clay minerals belong to the category of layered silicates or phyllosilicates. The strength of bonds between layers influence the plasticity of the different clay groups. They also vary in particle size, shrinkage and respond differently to firing. The major clay mineral groups are kaolinite, smectite or montmorillonite and illite. Kaolinites occur as primary and secondary clays and are formed because of intense weathering of the parent rock mostly due to acid leaching and are considerably wide-spread. Kaolinites have a two layered structure and their particle size is large when compared to other mineral types. While the plasticity of sedimentary kaolinites is good, residual kaolinites have low plasticity and their shrinkage is low. Kaolinites fire to white or yellow colour.

Smectites, formerly known as montmorillonites are characteristic of arid and alkaline environments and are not heavily weathered. The particle size of smectites is very small and they have a three layered structure. Smectites are very plastic and have a high shrinkage rate. When fired smectites attain cream, red and light brown colours.Illites occur mostly in marine and calcareous sediments and have a three-layered structure. They have considerably good plasticity and small particles. On firing, illites attain variable colours.he different phases of pottery production are discussed below

6. Obtaining raw materials

Obtaining raw materials for pottery manufacture is dependant on various factors. While the availability of good, workable clay is the most important factor, social organization also plays an important role in modern pottery making societies. Ethnographic studies have been conducted by Arnold, Kramer, Rye and others to understand the aspects of raw material acquisition. Arnold is of the opinion that potters obtain their raw materials from sources close to home. Clays are procured from 1 to 6 kilometers from the manufacturing site (Arnold, 1985). The mode of transportation employed plays an important role in the distance from which clay is obtained. Procurement of clay requires travel to the source, excavation and transport to the manufacturing site. Tempering materials are often transported from sources farther away because the quantity of temper is much lesser than the clay quantities. Some locally available temper like chaff, ash and grog are also used. Raw materials for decoration of pots like pigments, glaze are also acquired from long distances. A number of factors influence raw material procurement like the availability of the same, cost incurred in transporting the raw material and also importantly social and cultural perceptions of the materials (Sinopoli,1991). Although ethnographic studies shed important light on the aspects of raw material procurement, it is important to remember that the nature of clay deposits vary greatly in short spans of time and the cultural perceptions of modern day potting societies can not be completely applied to the protohistoric potting societies.

7. Preparation of raw materials

Clays contain impurities like pebbles, small stones and organic debris. Removing particles of coarse matter, including large inclusions, plant remains are involved in the initial processing. The extent of cleaning the clay to remove these impurities largely depends on the technology that is to be employed and also the thickness of the walls. For pottery that is handmade, clay which is a bit coarse can also be used. For pottery with thick walls too, considerably coarse clay can be used, while very fine clay is needed for thin walled pottery (Rye, 1981). Neolithic pottery, being handmade is largely comprised of coarse clay. Impurities are removed from clay either by hand-picking or by drying damp clays and pounding them and passing them through a sieve. A more elaborate technique of levigation where coarse impurities settle in the bottom and the fine clay mixed with water is separated is used in more recent times for very fine clay.

To improve the workability of the clay and add strength to the walls of the pottery, non -plastic inclusions are added to the clay. These include organic materials like ash, husks of grains, chaff as well as inorganic materials like quartz, lime and grog. The proportion of these non-plastic inclusions greatly varies with the plasticity from 20% to 50% of the total volume (Rye, 1981). Apart from the non-plastic inclusions potters also combine different clays to improve the plasticity and enhance the workability. Water is then added to the clay in order to make it plastic and then it is kneaded well. The kneading or blending of the clay is done to remove the air pockets and also to make the clay homogenous (Rice, 1987).

8. Forming techniques

Forming of pottery can be done in two ways, hand-building techniques and wheel-thrown techniques. There are various ways pottery can be made employing hand-building techniques and often more than one method is used in pottery making in the Neolithic. The simplest among the hand-building techniques is the pinching method where a lump of clay is held and from the center of the lump a hole is made and the walls are drawn using the thumb and fore-finger. This method can be used only to make small pots and walls of the pottery are randomly uneven.

Slab building technique is employed on both small and large pots with a non-round shape. In this method slabs of clay are joined together either by hand or with a paddle. Slab building technique also results in uneven pottery walls (Rye, 1981).

Moulds are used in hand-building techniques. Stones, broken pots, baskets and gourds are used as moulds. Prepared clay is plastered on either the interior or the exterior of the moulds and then dried to be separated. Mould-made pots can be made either in a single piece or can be made differently and then joined. This can be noticed archaeologically, either by the seam at the junction or the break which is more likely to happen at the junction of two different parts. Mould technique is best suited to construct restricted pots with narrow mouth (Sinopoli, 1991).

The most common of all hand-made techniques is the coiling technique. Narrow coils of clay are rolled horizontally on a flat surface. The diameter of the coils can range from 5mm to 10mm for thin-walled pots and to 5cm or more for thick walled pots. The length of the coil varies with the skill of the potter. The coils can be used to form the base or can be added on to a base formed by another technique. The walls of the pots are built by placing the coils successively one on top of the other. The coils moistened by the potter so that they adhere to each other. The joints of the coils are further smoothened by pressing with the fingers and/ or with a wooden or smooth stone. Care is taken to adhere the joints of the coils because it is at these joints that the pots are more likely to break during drying, firing or use (Sinopoli, 1991). Ring building is a variant of coiling technique. While coiling involves a spiral, ring building involves laying a series of circular coils on top of one another. It is very rare that this distinction can be noticed archaeologically (Rye,1981). In both coiling as well as ring building techniques the wall thickness varies greatly. Regular horizontal “corrugations” can be noticed if the junctions or coil joints are not obliterated.

Turntables are used by potters to slowly spin the pots to uniformly work on all the sides. More often than not more than one hand-building technique was employed and tools like smooth pebbles and sharp pointed tools were also used.

9. Finishing techniques

Like hand-building techniques there are different ways of giving a surface finishing to the pot. The forming techniques give the pot a basic form. A potter employs various finishing techniques to shape the pot and also decorate the pot. Finishing techniques to shape the pot are the paddle and anvil technique, trimming, scraping, shaving and turning.

The paddle and anvil method comprises the use of a rounded stone anvil and a wooden mallet shaped paddle. The anvil is held in the interior of the pot while the exterior is beaten by the paddle. This method is applied to pots when they are in a leather hard state when they are malleable but much of their plasticity is lost and thus the shape is not lost. This not only increases the diameter of the pot but also makes the wall of the pot thin and compact thus increasing the strength and also decreasing the porosity of the pot (Rye, 1981). This method can be used along with both hand-building techniques like coiling or slab building and also on wheel thrown pottery. Paddle and anvil technique is mostly used in producing round-based pots, mostly cooking pots.

The bases of pots are sometimes required to be thick and in these cases when the pot is in leather hard state finishing techniques like scraping, trimming and shaving are used to bring the base to the required thickness. Scraping involves removing quantities of clay with the help of a sharp instrument like stone or smooth edged pottery from thicker areas perpendicular to the pot in order to make the pot considerably uniform in thickness. On the interior walls of the pot marks from the scraping instrument can be noticed.

Trimming is a finishing technique involving cutting excess clay away with a tool and shaving involves removing excess clay from the exterior leaving angular facets on the pot surface (Rye, 1981). Thinning of the pots can be done by turning on a wheel. Each of the finishing technique leaves distinct marks on the pot walls.

The above described finishing techniques are aimed at mainly shaping the form of the pot and not at the aesthetics of the pot. The finishing techniques which affect the surface finishing of the pot are smoothing, burnishing and polishing (Rye, 1981). These techniques do not involve application of colour and uses a hard tool like a stone or a broken and smoothed potsherd in the process. The surface of the pot is rubbed against by the tool and this does not alter the shape of the pot but it conceals the irregularities of the walls of the pot (Sinopoli, 1991). Smoothing is non-lustrous and leaves the surface with a uniform and matte texture. Burnishing involves a lustrous effect on the surface of the pottery but the lustre is irregular and the facets left by the burnishing tool on the surface can be noticed. Polished pots are uniform and highly lustrous and no traces of the tool can be noticed (Sinopoli, 1991). These surface finishing techniques reduce the porosity of the pot by aligning the clay particles on the surface.

Other finishing techniques like slipping and glazing change the colour of the pot surface. Slipping includes applying a uniform coat of liquid clay all over the pot before firing. This not only alters the colour but also reduces the porosity of the pot. Surface finishing like smoothing, burnishing and polishing are also done on slipped surfaces sometimes like also painting and plastic decorations. Glazes comprise of silica, fluxes which reduce the melting point of the glazes and metallic oxides that provide colour to the surface of the pot. Glazing like slipping reduces the porosity of the pot. Glazing is not seen at all in the pottery studied in this work.

Decorative finishing techniques like painting, incising and appliqué designs are also seen in Neolithic and later pottery. While painting involves using natural pigments to recreate animal, plant and geometric designs on the exterior of the pot, incising is done with a pointed stylus-like tool on the surface of the pot. These finishing techniques are purely to enhance the aesthetic appeal of the pot and do not serve any functional purpose.

10. Firing techniques

Firing is the final stage of pottery manufacture. Pottery that are formed are usually left to dry in shade for a few days in order to let the excess moisture that is retained in the clay fabric evaporate. It is during this stage that the pots shrink and the non-plastic inclusions in the clay fabric reduce the shrinkage. The presence of non-plastic inclusions prevents the pottery from collapsing or warping. The pottery is dried before heat is applied to it to prevent the cracking and breakage of pots when the steam from excess moisture in the clay paste is released from the walls of the pot. Firing of pottery involves chemical changes of the clay body, resulting in a hard and durable product which can withstand repetitive heating and cooling. The final appearance of the surface of pottery largely depends on three aspects, the maximum temperature attained during firing, the duration of the firing process and also the firing atmosphere (Rice, 1987).

Firing can take place in many contexts. Pots can either be sun-dried or fired in open fires, in small pits or in bonfires, or in closed enclosures like kilns and ovens. Pots that are sun-dried are not durable and are very rarely found in archaeological contexts. Neolithic pottery is fired mostly in open-fires either in small-pits or bonfires. In open-firing, fuel is first laid out and the pots to be fired are placed directly on the fuel and are also covered with more fuel. The duration of the firing is short and so all the temperatures that are attained in these open-fires are not very high. The pottery that is fired comes in direct contact with the fuel and fire and also because the temperature is not uniform in all the places, it results in fireclouds or mottled colours on pottery (Rice, 1987).

The pots that are fired at low temperatures are more porous and coarse (Sinopoli, 1991). Rice is of the opinion that short firing of the open-fires is withstood by the Neolithic pottery because of their rather coarse texture. The large mineral inclusions in the clay paste increase the thermal shock resistance of the pot and thus can withstand the uneven and short firing episodes of open – fires (Rice, 1987)

The temperatures attained in open-fires are low and range between 600° and 850° C. The degree of temperature attained greatly depends on the fuel that is used. For instance fuels like dung, ash and certain types of wood when used can result in attaining temperatures of over 900° C (Rice, 1987). On the other hand Rye is of the opinion that although in open-fires hotspots are present, it is highly unlikely that temperatures rise beyond 1000° C (Rye, 1981).

A minimum of 550°C is needed to produce pottery for considerable hardness and durability. Many chemical changes take place at different temperature during the firing process. The fabric or the clay paste which includes the clay minerals, water and the non-plastic inclusions are affected by different temperatures. The moisture that remains on the surface of the pot is removed when temperature reaches between 200° C and 300° C. The water that is chemically bound to the clay particles is lost at higher temperatures. When temperature reaches between 500° C and 600° C some of the inclusions in the clay like carbon, sulfides and carbonates and salts are lost. The pots shrink by about 15% or more of their original mass at these temperatures. Irreversible changes in the clay structure occur at 500° C and above. Clay minerals start to decompose and edges of the grains bond together by ion diffusion which is known as ‘sintering’. While kaolinite decomposes and restructures at 585° C, smectite attains the same at relatively high temperature of 678° C (Rye, 1981). At 900° C clay minerals lose their structure and form new silicate minerals. Inclusions like quartz undergo major structural changes at 573° C, 867° C and 1250° C (Sinopoli, 1991).

When firing is complete, the pots are left to cool. Rapid cooling like rapid heating might result in breakage and cracking (Rye, 1981). The total time taken from the initial firing till the gradual cooling is considered as the duration of the firing and this plays an important role in the hardness and durability of the pottery. Rapid heating and cooling weakens the clay structure and can make the pot less hard.

The atmosphere of the firing context refers to the presence or absence of oxygen in the firing chamber. When oxygen is present, an oxidizing atmosphere exists and when there is very little presence of oxygen a reducing atmosphere exists. The firing atmosphere along with the presence of organic matter in the clay paste affects the pot colour, porosity, shrinkage and hardness (Rye, 1981). In oxidizing conditions, the organic matter in the clay and the fuels is burnt and a light colour is achieved. In reducing conditions, carbon in the clay paste is lost and the carbon from the fuels is also deposited on the surface of the pots resulting in black or dark brown coloured surfaces. The colour of the paste from the core to the surface also varies with the firing atmospheres.

The process of making pots involves many stages, the first of which is the forming process in which the pot is given its basic form. Normally this stage of pottery making is not seen as a surface feature because the marks of this are either masked or erased by later processes like burnishing and smoothing. However, in handmade pottery, the profile or the walls of the pottery are uneven and are not of uniform thickness. This characteristic of the pottery sometimes remains even after the later finishing processes.

11.Conclusion

In this chapter, we have discussed the fundamentals of pottery in archaeology. This includes its role as archaeological evidence, history of ceramics, its early development in Indian subcontinent and finally its production techniques.

Weblinks

• http://sites.udel.edu/materialculture/about/what-is-material-culture/
• http://www.encyclopedia.com/topic/Material_culture.aspx
• https://en.wikipedia.org/wiki/Archaeological_culture
• http://www.lib.niu.edu/1998/iht529802.html

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