Why Investigate the Origin of Pottery
A Study by Dr. Alexandria Tsolakidou
The building blocks of archeology are the remains of objects made from previous cultures. The work of the archaeologist is to interpret the fragments of pottery, stone tools and bones in relation to the place where found and compared with other archaeological data in space and time. Using various analytical approaches, the archaeologist trying to use archaeological evidence to reconstruct the technological level and economic organization of a given society. Ceramics are particularly useful in the archeologist because it is the most abundant finds in a dig. The clay is a cheap raw material that can be easily identified and its exploitation does not present particular difficulties. Once will undergo calcination, clay is the most resistant archaeological material, except of course for the objects are made of stones. Thus the ceramic survive in environments where the organics are decomposed and metal objects have been eroded. (Wisseman 1994)
Regarding the study of ancient pottery, an important first step to answer the basic questions of the distribution and exchange patterns, is to determine where it was built, namely the origin (Renfrew 1977, Riley 1984). The location of the production of ceramics is generally investigated with two very different ways of approach. One is to observe in space the distribution of sources of ceramic types (wares) or works of art associated with the production of ceramics, and the other to use analytical techniques (Peacock 1970, Rice, 1987).
An indication used by archaeologists for ceramics production sites, is the emergence in the field of ceramic molds. The criterion of relative abundance (criterion of relative abundance) states that ceramics have probably prepared in the area where their frequency is high and that initiated (trafficked) around this area. The prevailing assumption is that in most places the bulk ceramics are local. Another approach was based on the presence in the object associated with the ceramic activity such furnaces, molds, uncooked jars, broken jars or shells which have been fired to extremely high temperatures and therefore rejected around a kiln (kiln wasters) and shaping and grinding tools. The presence quantities of these objects, alone or together in a region is a logical and unquestionable indicator of a production location. (Rice 1987)
Origin of Studies
Studies origins are the analytical techniques based on so-called “office of origin” (the provenance postulate).
The “office of origin” claims that between different sources of raw materials can be identified in detail differences, and that variations in the chemical composition are greater between different sources than in the same source (Harbottle 1982, Bennett et al., 1989) .
The analytical techniques are commonly used to answer the question of the origin of pottery is the petrographic and chemical analysis.
The methodology of petrographic analysis comes from sedimentary petrology and considers the ceramic as a metamorphosed sedimentary rock. (Whitbread, 1995: 366). The performance of the ceramic in a raw material source is based on the composition of the inclusions. However, in the polarizing microscope ceramics considered not only in terms of mineralogical composition but also in relation to the microstructure and texture of the ceramic material.
This information can be derived, and conclusions on the manufacturing technology of the ceramic as the addition of non-plastic materials, mixing of different raw materials, etc. (Shepard, 1965, Riley, 1982). The possibility of petrographic analysis to correlate the mineralogical composition of the ceramic with a specific geological environment and technological information provided for the manufacture of ceramics are the major advantages.
The theory behind the investigation of the origin of pottery by chemical analysis is that the chemical composition of ceramic which have been fired directly related to the chemical composition of the raw material from which constructed. However, it is widely recognized that transforming ceramic clay is a complex process which involves many factors affecting this direct correlation (Pollard and Herron, 1996).
So the usual procedure followed in provenance studies is to compare the chemical composition of the ceramic is not with some raw materials from which can be built but with the chemical composition of ceramic whose origin is known (control or reference groups). One of the main objectives of the chemical analysis of ancient pottery is to perform its chemical composition in a control group, if any.
Because it is necessary to combine the techniques? A ceramic shell is a complex system. Its chemical composition is a function of the chemical composition of the raw materials from which it is built, pre-treatment suffered by the clay to remove unwanted material and to obtain the desired texture (Blackman, 1992, Neff et al, 1988 & 1989 ) of firing, which may affect the setting through the volatilization of some components (Kilikoglou et al. 1988) the contents during use, changes that may have occurred during the course of the burial in the ground (Buxeda et al., in press) and sometimes the treatment suffered after excavation (Maggetti, 1982). Therefore, the interpretation of the results of the chemical analysis is complicated and can not be associated directly with the mineralogical characteristics of the raw materials used by ancient potters. (Whitbread, 1995, pp. 251). When a shell is analyzed, and the composition is compared with that of a control group can be found that is compatible or not. If the composition of the shell is not compatible with the establishment of the reference group may be this could mean either that the sample has been introduced or is local but its chemical composition has been altered due to factors that affect the shell after firing (Buxeda et al ., in press). Or it may mean that its composition represents another initial recommendation has not been altered but not represented by some of the existing reference groups (Maggetti, 1995). In both cases, the examination of the thin section of the shell under the polarizing microscope, can help by directing the right answer, because to some extent, allowing direct observation of the causes of the variations of the ceramic material. (Whitbread, 1995: 251).
Ideally the analysis of ceramics should be done with chemical and mineralogical techniques. Initially the mineralogical and chemical techniques were applied independently to provide answers to questions of origin. This is attributed mainly to the fact that each of the two techniques successfully applied in different kinds of pottery (Jones, 1986). Chemical analysis applied successfully in fine and neat ceramics, and is less suitable for the characterization and very coarse sandy ceramic because of their extreme heterogeneity. The petrographic analysis applied to coarse or relatively coarse pottery. While it is generally correct that the petrographic and chemical analysis applied to coarse and fine ceramics respectively, both techniques have yielded good results after their application in cases pottery belonged to the same for any technical type (Riley 1982, Thierrin- Michael, 1990). In many cases where a technique failed to differentiate two ceramic groups the other was successful (Prag et al., 1974). This caused long discussions about what is the best method for the characterization of ceramics and type of information extracted from each method. Soon it became apparent that the two techniques are complementary. For a better understanding of the final composition of the ceramic and to answer the question of their origin should be used both techniques in the study of ceramics. (Rice, 1987: 413-418, Jones, 1986: 55-56, Knapp and Cherry, 1994: 15-40, Maggetti, 1995, Whitbread, 1995: 252, Pollard and Herron 1996: 107). As a consequence of this finding, the latest studies of the origin of ceramic two techniques are used very often complementary (Day et al., 1999, Tsolakidou, 1999, Tsolakidou et al., In press).
From what has been stated above it follows that a necessary condition to become a study of origin is to have pottery known origin. For this reason, one of the first steps when starting the study is to form reference groups. Traditionally, reference groups are ceramics considered local to a position and the entopoiotita is determined by archaeologists based on the following criteria:
– That is found in large quantities in one location is local (criterion of relative abundance)
– The coarse pottery in one location is local
– Pottery associated with verified manufacturing facilities (such as ovens) is local
To qualify archaeological ceramic type as a native is sometimes easy and can be done safely (when it comes to pottery that has some unique styling features or signature). Many times, however, must be indirectly used tricks. One way is to analyze a number of ceramic objects from the same place and then become grouping of objects in populations with different composition. When one of these groups contains the majority of objects considered to reflect the local pottery (Wilson 1978). This may in some cases be sufficient, particularly when the recommendation that dominates covering ceramic large time range, but is a way of inductive and becomes problematic when two or more types of recommendations are present in the same population sizes. A potential method to overcome this problem involves the characterization of the recommendations of natural clays in deposits located near the site of interest. (Neff et al., 1992). H necessity of analysis and clays with ceramics has been extensively discussed by many authors (Boardman and Schweizer 1973, Prag et al., 1974). It is generally desirable, apart from the study of ceramics, to study and included regional location of clay deposits when possible (Wilson 1978).
Once formed in ceramics control groups followed by analyzes.
In these analyzes, the establishment of a group of objects is determined by sensitive methodological and chemical techniques to obtain a fingerprint unique for this recommendation and, by extension, the geological source. Eventually the two groups with the characterized data ceramic electric unknown origin and ceramics known position- compared statistically to determine the possibility that the chemical compositions of known and unknown groups represent a geological / geochemical population (Bishop et al. 1988). This is done by using complex mathematical techniques, developed gradually be applied to Archaeometry data and give groups of objects, whose interpretation will be able to solve archaeological problems (Mommsen 1988, Baxter 1994, Beier and Mommsen 1994, Buxeda, 1999).
The problem of the origin of ceramic presents great difficulties to the solution of one and even today the local market (or cheaper) counterfeit items were created by recognized names in the market can be of great economic interest (Rice, 1987). Identifying the manufacture of some pottery therefore not always easy. Therefore one of the most important applications of analytical chemistry in archeology is to detect the main elements, secondary elements and trace elements for reasons relating to the determination of origin – ie the location from where the raw materials came from. One of the largest groups of archaeological materials were analyzed and analyzed are ceramic.
The main analytical techniques used to determine the chemical composition of the ceramic to answer the question of the origin is the neutron activation analysis (Neutron Activation Analysis), the analysis by fluorimetry X-Ray (X-Ray Fluorescence Analysis) and Spectrometry Plasma Inductive Coupling (Inductively Coupled Plasma Spectrometry).
Analysis by Neutron Activation (N.A.A.)
The study of the origin by chemical analysis based on the determination of primary and secondary elements and trace elements. However it is generally accepted that the concentrations of trace elements are better to differentiate two ceramic groups have different origins. Because therefore the possibility given by the neutron activation analysis to determine a large number of trace elements with good accuracy and repeatability, the technique has become the most popular among the elemental analysis techniques for such studies. The majority of laboratories involved in ancient pottery provenance studies use the ANE as the main analytical technique.
When a material is bombarded with neutrons, charged particles and photons can be converted by a nuclear reaction to a radioactive isotope of the same or another element. In the case of irradiation with neutrons usually converted into heavier isotope of the same element. The excess energy is liberated in the form of gamma rays. Usually, though not always, the new isotope is radioactive and the measurement of intensity is an estimation of the quantity of the element A present in the radioactive material. As neutron sources generally used nuclear reactors. Neutrons are used for irradiation are neutrons low energy (thermal), and the probability of each element to recruit neutrons remains constant.
The relationship between intensity of radioactivity and mass is linear. Despite the linearity between but for the calculation of the mass of the isotope required knowledge of many experimental and nuclear parameters and therefore the calculation is made by comparative methods. In the comparative method, a known amount of the isotope to be determined is radiated under the same conditions as the sample. Thus all the experimental and nuclear parameters between the sample and the standard substance can be considered similar and the reasons for the tensions of the radioactivity of the sample and of the standard substance can be considered equal to the ratios of the masses of the isotope. All that is required is to make a correction between the decay time of the radioactivity in the sample and the standard substance.
Analysis by X-ray fluorometry (XRF)
The X-Ray fluorometry is a technique for the analysis of the bulk material. Samples were prepared as compressed powder tablets or tablets and fused glass induced by X-rays generated from a lamp (tube) X-Ray operating at a potential of 10-100 kV. Interaction of the primary radiation with the atoms of the sample causes ionization electron orbitals distinguished. During the decay of electrons in the basic state emitted X-rays characteristic of the element. The radiation intensity measured by a suitable X-ray spectrometer, and compared to the corresponding radiation of the standard sample. This technique is one of the most widely used instrumental analysis techniques siliceous materials and to identify both primary (Na, Mg, Al, Si, P, K, Ca, Ti, Mn, Fe) elements and selected trace (Rb, Sr, Y, Nb, Zr, Cr, Ni, Cu, Zn, Ga, Ba, Pb, Th, U).
Analysis by inductively coupled plasma spectrometry. (ICP)
The inductively coupled plasma spectrometry recorded as an analytical technique with outstanding features. The unique properties resulting from the excitation source using the argon plasma inductive coupling. The sample is transferred to the plasma through the central gas flow, in most cases, in the form of an aqueous solution is partially converted into very small droplets by means of a nebulizer. What is introduced in the plasma is an aerosol of the sample into the argon. In the plasma the sample is vaporized and atomized, followed by excitation and ionization. The polychromatic radiation emitted from this excitation is separated into different wavelengths and is measured by a photomultiplier to extract information on the sample.Quantitative determination of the composition of the sample is calculated by comparing the intensity of the sample radiation to the calibration curves. Calibration curves are constructed after measuring the intensity of standard solutions of known concentration (Thompson and Walsh 1989)<