ON POLISH X-RAY FLUORESCENCE ANALYSES OF THE CHEMICAL COMPOSITION OF LATE MEDIEVAL AND MODERN POTTERY
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The X-ray fluorescence analysis (XRF), also called X-ray spectrometry is applied currently also to pottery research, including analyses of Late Medieval and modern ceramics. Also considered in the deliberations were analyses by other methods like the spectral method and flame photometry. The most important issues taken up by individual researchers include, on one hand, factors influencing the correctness and reliability of analyses and, on the other hand, ways of interpreting results and making inferences from them. They concern ways of carrying out analyses, starting with sample preparation, strengths and weaknesses of applied methods, as well as chemical compounds which need to be determined in order to collect information on the characteristics of clays and glazes, the number of samples that are indispensable for a proper analysis, the possibility of establishing similarities and differences in the chemical composition of products from the same centers or regions of production. The analysis is characterized primarily by the possibility of examining small amounts of products, resulting in only insignificant damage to the object, and even very small, selected parts of the sample, both on the surface and in the break. Preparation of a sample is relatively simple and time needed for making the determination is a few minutes. As for potential element detection and accuracy, technologists are of the opinion that analyses by the described method are in some cases similar to or more accurate than classical analytical or other instrumental methods. The flaws of this method draw mostly from the way the samples are prepared. The method is a surface analysis, hence its correctness is heavily dependent on the quality of the examined surface, which should be as smooth as possible. Impurities and rough spots can lead to errors of analysis, raising the content of some components and changing the mutual proportions of others. Mechanical cutting of samples from ceramic products, especially in the case of vessels glazed on both sides, can lead to contamination of the ceramic mass with particles of glaze and the glaze with components of the ceramic mass. The results of analyses can be disrupted in X-ray spectrometry as well, mostly in effect of the matrix and granulation. Difficulties in determining light elements constitutes another limitation of the method. The element detection range also does not make this method suitable for determining elements with a content below 0.01% weight in a given sample. Normalizing the results to 100% creates in turn the impression of an errorless analysis. The multiple character of observations in reference to a single sample and whole series of samples is of significance. It is important to observe similarities or differences of results depending on the size of the analyzed surface and its position, in order to determine optimal, general and binding conditions for carrying out the remaining analyses. Upon obtaining different results concerning the content of specific elements, it is essential to consider different reasons for this; was the sample actually representative of a given set of finds, does the analyzed product correspond to other finds in terms of technique and technology, did the spot that was analyzed contain impurities or not.
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