Tempering with XRF measurements: A study on the influences of temper in X-ray fluorescence measurements on ceramic  objects

Archaeological ceramics are often analysed with a portable XRF spectrometer to determine their chemical composition, even though they can be tempered with various different inclusions. To determine the influence of these tempers on the results of XRF measurements an experiment with test bars was set up. These test bars were made out of two distinct types of clay and a mix of these clays, and out of seven different types of temper present in the sizes 0 to 0.6 mm and 1 to 1.6 mm. These tempers make up 0 %, 5 %, 20 %, or 40 % of the test bar. The test bars were then fired at 850 °C and afterwards measured with a portable XRF spectrometer. Each test bar was measured three times so the variability could also be assessed. The temper types of basalt, muscovite, calcite, and plant material had the biggest influence on the XRF measurements and caused test bars to fall outside the 95 % confidence area of their clay type or even all clay types combined in a PCA plot. With basalt temper the...Show moreArchaeological ceramics are often analysed with a portable XRF spectrometer to determine their chemical composition, even though they can be tempered with various different inclusions. To determine the influence of these tempers on the results of XRF measurements an experiment with test bars was set up. These test bars were made out of two distinct types of clay and a mix of these clays, and out of seven different types of temper present in the sizes 0 to 0.6 mm and 1 to 1.6 mm. These tempers make up 0 %, 5 %, 20 %, or 40 % of the test bar. The test bars were then fired at 850 °C and afterwards measured with a portable XRF spectrometer. Each test bar was measured three times so the variability could also be assessed. The temper types of basalt, muscovite, calcite, and plant material had the biggest influence on the XRF measurements and caused test bars to fall outside the 95 % confidence area of their clay type or even all clay types combined in a PCA plot. With basalt temper the influence is especially high in calcium which can be increased, manganese which is increased, and cobalt which can be both increased and higher in variability. With muscovite temper the influence is especially high in phosphorus which has a higher variability, kalium which is increased, and rubidium which is also increased. With calcite temper the influence is especially high in calcium which is both increased and has a higher variability, manganese which can be decreased, and zinc which has a lower variability. With temper made from plant material the influence is especially high in phosphorus which is increased and can have a higher variability, calcium which can be both increased or decreased depending on the clay type, and zinc which can be both increased and have a lower variability. The influence of temper sized 0 to 0.6 mm on the XRF measurements was bigger than the influence of temper sized 1 to 1.6 mm. As expected the influence of temper on the XRF measurements increases along with the percentage of temper in which 40 % temper often has an especially noticeable influence. Ceramics tempered with higher percentages of muscovite, calcite, quartz, and plant material in smaller sizes can therefore cause problems in their provenancing. Other temper types and lower percentages of the mentioned temper types in bigger sizes can also cause problems in the differentiation of clay types by PCA, especially if clay types are similar to one another. With granite temper influences can be visible in the amount of sulphur, calcium, manganese, iron, cobalt, and strontium. With quartz temper the influence is especially high in calcium which has a higher variability, manganese which can be increased, and zinc which can be increased and is lower in variability. With grog temper influences can be visible in the amount of calcium, manganese, iron, cobalt, barium, and led.Show less

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Tempering with XRF measurements: A study on the influences of temper in X-ray fluorescence measurements on ceramic objects