Scientific Approaches

This approach focuses on extracting the evidence which is hidden in the pot itself. As seen above, other approaches to ceramic studies can go so far and no further, so the application of scientific methods of analysis has allowed breakthroughs in ceramic studies which were never thought possible. For example, specific provenances and production sites can be identified with certainty; sherds can be compared with other analysed sherds, thereby enabling the matching of different sherds of the same vessel, which may never have been brought together before; production methods can also be revealed, and this is particularly helpful with glazed ceramics, where the body is hidden beneath its glassy exterior: production methods include the temper added in the preparation of the clays, composition of the glazes, the firing temperature, and actual techniques of vessel formation. Lastly, this approach identifies important constituents that make it possible to conduct practical experiments, which enhance our understanding of the skill of the potter, and enable us to draw conclusions about the social or intellectual circles in which he lived (see below: Section C: Ethnographic Approaches).

This section attempts to provide an overview of different methods of scientific analysis that are currently applied in the study of ceramics. It is not meant to be comprehensive but only outlines those methods which today are most commonly applied in this area; nor does it try to give too scientific an explanation of each method, only what is sufficient for the non-scientist to understand what is going on in a particular method. At the end of the section are some examples of studies where certain analytical methods have been applied.

Many of these methods were developed to enhance understanding in other fields, especially medicine, but also petrology; the study of rocks and minerals to identify fuel-rich regions of the world. Early applications of some methods were in investigations of mummified remains, especially those too fragile to be unwrapped or removed from their cartonnage, and from here the use of these methods in museum studies spread to ceramics, where the results have been very sucessful. These methods are often used in conjunction with each other to give more accurate results or to screen a large selection of samples before applying more destructive methods of examination.

i.	Petrography:

This method provides valuable mineralogical information on the fabric of a clay, mainly by identifying the inclusions within it. A thin slice is cut from a pot and fixed to a glass slide. It is then ground to a thickness of 0.03mm: this is called a thin section. Many minerals are translucent at such a thickness and may be examined in a polarising microscope, which passes light through the sample and identifies certain minerals according to their optical properties. It can thus enable the identification of a provenance for the pot, by establishing the principle mineral components of the sample (the petrofabric) and comparing this with mineral deposits of a certain area. This method is most efficient when combined with other non-destructive methods, such as radiography, which can give a broad survey of a large collection of samples, from which a few important samples are selected for closer examination.




ii.	Neutron Activation Analysis (NAA):

This is a method of chemical analysis which identifies trace elements in a sample. A small amount (typically c. 50 mg) of powdered ceramic is extracted using a fine drill, placed in a nuclear reactor and bombarded with neutrons; as a result gamma radiation is emitted which can be measured to determine the concentrations of various elements. This is a minimally destructive process which has long been favoured for its high precision and accurate results, but alternative techniques are now being sought due to the closure of civil nuclear reactors.

i.	Radiography:

This process creates a film image of those internal features or parts of a ceramic object that differ in their composition/thickness and thus their capability for transmitting X-rays. It is the same process as using X-rays in a hospital. The varying amounts of X-rays that are transmitted by different portions in an object are recorded on film as different grey levels of exposure, and it is therefore a helpful method for investigating the texture of a clay body and the techniques of vessel formation. The various methods of forming a vessel each result in the generation of characteristic orientations of particles and voids within the clay body: for example, wheel-forming produces a spiral pattern running around the vessel, as the voids and inclusions in the clay are drawn up by the rotating wheel. These patterns can be exposed clearly by radiography. It also shows how additions such as handles were attached to the body, exposes joins between coils or slabs, fracture systems, thicker or thinner sections, hidden walls or repair systems; also particle size, paste texture, coil size, and can tell whether the clay has been kneaded. Xeroradiography is a newer development of this method, which improves image contrast and resolution of the film image. Radiography has the advantage of being very cheap, and non-destructive: it can therefore be used to examine complete or fully restored vessels without damaging them. When used in conjunction with petrography it can provide a broad survey of a large collection of samples, from which a few important samples are selected for closer examination (see Scientific Case Studies: (Xero)Radiography: Applications in Museums).




ii.	Scanning Electron Microscope (SEM):

This method is essentially non-destructive but is often used to analyse thin sections from clay bodies or glazes. An SEM is a microscope based upon the interaction of a beam of electrons (rather than light) with the surface of a material, which produces a black and white image. It has a very high magnification and thus allows examination of chemical elements present in a ceramic sample. These chemical elements can be distinguished according to differences in atomic number which show up as different shades of grey: eg. quartz appears darker than glaze and glass elements which have higher atomic numbers. This technique is being used increasingly used in the examination of glazes, since their susceptibility to weathering and decay makes other methods of analysis unsatisfactory. It is possible to record still images from the SEM, known as "photomicrographs".




iii.	Spectrometry:

This method identifies chemical elements present in a sample by analysing the electromagnetic spectrum of radiation emitted or absorbed by a sample whose atoms have been excited under specified and controlled conditions. There are several methods, based on examining different aspects of a sample’s electromagnetic spectrum: eg. fluorescence spectrometry analyses the visible or invisible radiation produced in the form of X-rays or ultraviolet light. According to the conditions, this radiation may be absorbed or emitted by the sample in varying quantities. The radiation is measured by separating it into constituent wavelengths which allow its chemical ingredients to be determined. The method can analyse upto 30 elements in one sample, ranging from major to trace constituents, usually with high precision results; however there is some variation in the efficiency of spectrometry according to which method is used, the conditions and material. Some methods of spectrometry entail the removal of a sample from the vessel to be analysed, and are thereby destructive, while other methods allow the artefact to be analysed directly without destruction.




iv.	X-ray diffraction:

This is another method used to identify the mineralogical components of a ceramic object. A sample is bombarded with X-rays which are diffracted (ie. scattered) at the edges, points or planes of the object, at angles which are characteristic of the spacings between the atomic layers in the crystal lattice of the object. The resulting pattern can thereby be used to identify the minerals present in a sample, with some indication of the concentration of the particular minerals according to differing intensities.




v.	Xeroradiography:

This method was originally developed for medical applications, particularly mammography. An aluminium plate is used to record the X-ray image: this plate is conditioned with an electrostatic charge in such a way that it attracts either positively charged or negatively charged particles. The object to be analysed is placed on top of the plate and exposed to X-ray beams. An image is left on the surface of the plate according to differences in the radiographic density of the object. This image is exposed to a fine powder which is attracted to the charged areas on the plate in such a way that the powder heaps up on one side of a charged line, and leaves only a thin amount on the other side of it. This results in edge enhancement on the developed image, which is the principle advantage of xeroradiography over radiography. The image is developed off the plate and heat-sealed on to plastic-coated paper, allowing the aluminium plate to be reconditioned and re-used. Xeroradiography is a helpful tool in ceramics analysis for all the same reasons as radiography (reveals the nature and distribution of voids and inclusions, presence of fractures or hidden walls, characteristics of vessel formation) with the added advantages of improved resolution and edge enhancement, which are the two common shortcomings of radiographic imaging.

i.	Radiocarbon (or C14) Dating:

This is the best known method used in the dating of objects from the archaeological record. It is based on the determination of amounts of C14 in a sample and is therefore only applicable to objects with a substantial quantity of organic matter in their composition. Thus it cannot be applied to ceramic studies.




ii.	Thermoluminescence:

This is a method used in dating as it allows the determination of the time that has elapsed since a ceramic object was fired. When a sample is heated it emits light, the amount of which is dependent on the natural radiation to which the sample has been exposed since it was last heated (when the clay was fired into a ceramic). It is a complex and demanding method which requires the accurate determination of a range of variables, such as the dose of radiation in the environment and the natural internal radiation of the object itself.