Monday, 11 October 2021

POTTERY: DIRECT EVIDENCE OF LIFE (#ceramics)(#chemistry)(#ipumusings)

POTTERY: DIRECT EVIDENCE OF LIFE

POTTERY: DIRECT EVIDENCE OF LIFE (#ceramics)(#chemistry)(#ipumusings)


Author: Anushka Singh

ABSTRACT 

The earth is strewn with fossil remains of extinct species. Pottery in an archaeological context most often concerns the fragments, or sherds, of ceramic vessels, but archaeological ceramics also include such things as drain tiles, roof tiles, ossuaries, coffins, stands, lamps and figurines, many of which lie in the precincts of vessels only in a broad framework. The enormity of the archaeological artefacts places a constraint on recovering the past, however, the excavated sherds and fragments themselves become a sherd of the past and thus act as a lens providing a clear insight into the past.


THEORY

Pottery, the first synthetic material humans created, an artificial stone, combines the four basic elements identified by the Greeks: earth, water, fire, and air. Pottery has transformed a broad range of human endeavours, from prehistoric cuisine to the twentieth-century aerospace industry. The term “ceramic” traces its roots in the Greek keramos, which are dubs as “burned stuff” or “earthenware”; it describes a fired product rather than a clay raw material. An air of uncertainty circumvents around why ceramics become important when they did in human history. Ceramics is a subjective term, its range differs vis-à-vis discipline. In archaeology earthenware, terracotta, stoneware, porcelain, and other materials made from fire clay and transformed/hardened by heat is termed ceramics. Diasporic trends amid nomadic communities might be a crucial factor in escalating the importance of ceramics—a fragility susceptible to break easily makes them difficult to be carried around, thereby easily being discredited among the mobile hunter-gatherers. In addition, certain foodstuffs, particularly seeds and grains, may be most effectively processed and consumed when cooked with water, and ceramics are very effective for such food preparation techniques. 

Pottery has been tremendously important in archaeological research for over a century owing to its abundance and indestructibility. It is a succinct compendium of technical, artistic, cultural, and economic choices. The choices directly reflect on the status quo ante and reveal significant details of prevailing circumstances and trends. Archaeologists and antiquarians quickly recognize that variations in ceramic forms and decoration were restricted in space and in time. Environmental variability stimulates evolution and is of fundamental importance from an archaeological perspective. Temporal or spatial variability suggestively affects the competition dynamics in populations and gives rise to disingenuous interpretations. Spatial variations could be used to clearly discern and characterise different prehistoric regions, whereas temporal variations could be a stepping stone in outlining chronological sequences within those regions.  Ceramic use and manufacture emerged individualistically in many parts of the world, and the knowledge of techniques for producing the ceramics were exchanged among societies, thereby explaining the significance of these relics as a cornerstone. A consolidation of the ubiquity and excellent preservation of pottery in archaeological contexts, directly makes them the most common materials that archaeologists recover in research. 

Pottery answers some of the most sought after questions in a very detailed manner. The details of chronology, trade networks, and/or the technology of the settlement from which they were recovered are just the surface of facts that can be unravelled with the help of ceramic artefacts. 

BASIC OBSERVATIONS MADE FROM CERAMIC ARTEFACTS

  • Segmentation and Orientation: Post-depositional conditions may crush the pots into fragments and sherds. In order to carry out analysis, it is important to have a model of the relic excavated. Using different techniques pots are reconstructed, which needs identification of segments—whether it is lip, shoulder, neck, handle, etc. 

POTTERY: DIRECT EVIDENCE OF LIFE (#ceramics)(#chemistry)(#ipumusings)
Fig. Anatomy of a pot


  • Lip/Rim: The narrow surface most distant from the base as measured along the centre of the vessel walls.
  • Neck: A constriction of the vessel below the orifice but above the maximum diameter of the body or shoulder.
  • Shoulder: The region lying between the body’s maximum diameter and the neck or rim. 
  • Handle: An appendage attached to the (usually exterior) wall of the body, neck or rim that apparently aided in the vessel’s manipulation. 
  • Base: the portion from the lower part of the body to the points that would normally be in contact with a surface when the vessel is at rest.
  • Size: The relevance of a pot/vessel depends much on its size and morphology; this can give away its significance. To measure rim or base diameters, a diameter chart comes in handy. There are arcs corresponding with various diameters, flowing in ascending order, typically at 1 cm intervals, as well as radial line segments to indicate the proportion of the circumference that each rim or base preserves—a useful measure for calculating the degree of fragmentation.

POTTERY: DIRECT EVIDENCE OF LIFE (#ceramics)(#chemistry)(#ipumusings)


Fig. Use of a diameter chart to estimate the diameter of circular rims or bases as well as their maximum horizontal preservation as a percentage of a full circle. 

(Source: Portable Antiquities Scheme)


  • Vessel Shape: Based on the angle between the rim and horizontal plane, a shape can be generically bifurcated as everted (outward leaning), inverted and vertical. Common shapes that have been identified so far are bowl, jar, beaker, platter, others (lamps and stands), and non-vessels (figurines and statues).

POTTERY: DIRECT EVIDENCE OF LIFE (#ceramics)(#chemistry)(#ipumusings)

Fig. A simple template for classifying vessels by the degree of “openness” for whole and reconstructable vessels. 


  • Fabric: The durability and significance begin with the selection of raw materials, the kind of clay used. Ceramic fabric descriptions record significant geological properties of the raw materials, the potters' technological choices and actions such as preparation of the clay body, vessel construction, and firing. Synthetic in origin, the constituents of ceramic fabrics reflect the geological characteristics of the regions from which the raw materials were obtained. Petrographic analysis can be carried out. This can clarify four things:
    • The non-plastic inclusions (mineral and rock fragments contained in the seeds, which are visible using optical microscopy)/temper (fragments which are deliberately added to the paste): minerals and rock fragments, organics.
    • The matrix/microstructure or paste: the original clay used for firing. 
    • Porosity: a result of the production process and raw material properties. 
    • Surface decoration or treatment such as slips, glazes and paint.
  • Signs of forming: The construction of a pot can be done by numerous methods in two steps-primary and secondary forming. 
    • Primary forming includes laying out a rough draft of the final shape. Following are the methods of primary forming:
      • Pinching & Drawing
      • Coil building
      • Slab building
      • Wheel fashioning
      • Wheel throwing
      • Mould forming
  • The final touch of elegance and decorations come under secondary forming. This can be done in the following ways:
    • Joining
    • Beating
    • Scraping
    • Trimming
    • Turning
  • Finishing methods: Once formed, preforms of vessels can undergo one or more techniques to alter their surface characteristics. Smoothing, burnishing, impressing, rouletting, incising/combing, piercing & cutting, applique, slipping & painting, and glaze are techniques to enhance the surface of a vessel. 


EVALUATING CERAMIC PROVENANCE

The provenance of an artefact refers to the origin, the source and can be the place where it was found in the excavation, an indispensable piece of information; the term might refer to the place of manufacture. Discovering such information can unravel evidence that can lead to an understanding exchange and interaction among past human groups. Traditional ceramic studies classify pottery by its physical characteristics, such as form, fabric, and decoration. These attributes can be so exclusive and distinguishable that often the shape of the vessel can be discerned with the help of a sherd. Pottery characteristics metamorphose and can often be a trademark, representing a particular region. Advanced analytical techniques prevent unnecessary hassle and give unparalleled accuracy. Some of the techniques are as follows: 

  • Ceramic Petrography: A well-established research technique needing a standard "polarizing light microscope;' equipped with a circular rotating stage, two polarizers, and a Bertrand lens or phase telescope, allows the construction of large, relatively inexpensive reference databases. The economic propensity of petrographic analysis qualifies it for a classification technique of ceramics, by both qualitative and quantitative detection of mineral inclusions and rock fragments. Relevant information regarding the nature of inclusions and temper materials can be obtained using thin-section petrography. 
  • Ceramic Micropalaeontology: The existence, amount and nature of microfossil accumulations are dependant upon the types of raw materials used in pottery manufacture, the debilitating conditions predeposition of the raw materials, and on the methods/technologies employed in the construction of the artefact. The biomineralized shells and skeletons (composed of calcite, silica, apatite, or resistant organic compounds) may be preserved contrariwise to the non-mineralized tissues that usually disappear shortly after death. Micropalaeontological groups include representatives of all kingdoms. So far, microfossils have been studied with a petrological or biological microscope; the critical factor is the type of microfossil, albeit electron microscopy allows the finest details to be viewed.
  • Electron Microprobe Analysis (EMA): Archaeoceramics such as jars, cups, pots, plates, amphorae, statuettes, etc., are, generally made of a clay-based body, may or may not revolve around the involvement of tempering material, fired at relatively high temperatures, and therefore practically can be regarded as an artificial rock formed through anthropogenic pyrometamorphism. Electron microprobe is efficient in analysing the matrix, the clasts, and the firing phases in archaeoceramics. Electron microprobe provides insight into the composition of mineral phases using a narrow electron beam to stimulate the emission of X-rays. 
  • X-Ray Powder Diffraction (XRPD): The atoms in ceramics are bound together predominantly by strong covalent forces to form either crystalline compounds or amorphous (glassy) solids with undefined order, disoriented symmetry and periodicity. The kind of atoms present in an objet d'art describes its elemental composition. The knowledge of the phase composition of ceramics can be used to estimate firing temperature ranges, by observing the formation or decomposition of particular minerals and establishing provenance groups based on their mineral composition. Analytical techniques such as X-ray diffraction (XRD) are required to determine the phase composition of ceramics. 
  • Laser Ablation-Inductively Coupled Plasma-Mass Spectroscopy: Elemental "mapping" and phase analysis by LA-ICP-MS largely aims at the identification of the underlying chemical structure and mineralogy of a ceramic. The techniques discussed above have relatively high detection limits and cannot typically measure elements present at very low concentrations that are often of interest in ceramic compositional studies. LA-ICP-MS has consequently emerged as the preferred technique for targeted analysis of archaeological ceramics owing to the wide range of elements it can measure, low detection limit, and minimal destructiveness. 
  • Instrumental Neutron Activation Analysis (INAA): Neutron activation analysis (NAA) is a nuclear science technique for determining the elemental composition of ceramic, clays, and other materials. The technique works by exposing a small amount of sample material to the neutron field within a nuclear reactor, in order to activate/create radioactive isotopes of the elements that are present in the relic. Identification and precise quantification of the elements formerly embedded in the sample can be brought about by closely monitoring the subsequent decay of these radioisotopes. Assimilation of contributing factors like simultaneous multi-element analytical capacity, sensitivity, precision, and ease of sample preparation weigh into the popularity of INAA.
  • Fourier Transform-Infrared Spectroscopy: The factor that gives this method an upper hand is short analysis time which goes on to mean that researchers obtain results almost immediately, and owing to the portability of the equipment, the analysis can be done in the field. The banality of this technique lies in its ability to identify the composition of both crystalline minerals as well as the pseudo-amorphous phases of the fired-clay ceramic. Furthermore, analysis by FT-IR spectroscopy is almost non-destructive for the artefacts since it requires only a small amount of ceramic material. 
  • Organic Residue Analysis (ORA): Apart from vessel production, use and provenance this analysis project a vignette in the context of diet and subsistence practices, as well as the ancient trade of goods and raw materials, technology, resource procurement /exploitation, and the domestication trends of plants and animals, etc. The term ‘organic residues’ is used to describe a range of amorphous organic remains from diverse natural sources, associated with a variety of artefacts found at archaeological sites. An amorphous nature implies a lack of clearly discernible morphological features. The organic residues can be obtained on the site, from the carbonized, encrusted residues clinging to the surface of a vessel, or can be preserved within the vessel wall, known as absorbed residues. Absorbed organic residues are a major source of ORA. 


CONCLUSION

Owing to its ubiquity, abundance and durability, pottery has been a trusted window to peek into history. Once excavated, analysis (destructive or non-destructive) of the relics can be done post-reconstruction. Various measures to ensure the safety of evidence are taken. The minutiae are extremely important in order to answer archaeologically significant questions regarding ethnography, use and activity distribution, social and political organisation, etc. 


REFERENCES:

📌 Price, T., & Burton, J. (2011).An introduction to archaeological chemistry. New York, NY: Springer Science+Business Media, LLC. (Buy at Amazon)

📌 Pollard, A., & Heron, C. (2008).Archaeological chemistry /cA. Mark Pollard, Carl Heron(2nd ed.). Cambridge: Royal Society of Chemistry. (Buy at Amazon)

📌 Hunt, A. (2019).The Oxford handbook of archaeological ceramic analysis. Oxford: Oxford University Press. (Buy at Amazon)

📌 Banning E.B. (2020) Ceramic Artifacts. In: The Archaeologist's Laboratory. Interdisciplinary Contributions to Archaeology. Springer, Cham. (See link)

📌 Dunne, Julie & Evershed, Richard & Heron, Carl & Brettell, Rhea & Barclay, Alistair & Smyth, J. & Cramp, L.. (2018). Organic Residue Analysis and Archaeology Guidance for Good Practice.  (Check at Amazon)

📌 Rice, P. (2015).Pottery analysis(2nd ed.). Chicago, Ill.: The University of Chicago Press. (Check at Amazon)


About the Author:


Anushka Singh, a graduate student of the University School of Chemical Technology, GGSIP University, Delhi. She is pursuing her graduation in chemical engineering. 



👉See Also:


No comments:

Post a Comment