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Phosphates and archaeology
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Accuracy and validity of the methodology
Performing a phosphate analysis survey
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Interpretive possibilities
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Summary
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Phosphate Analysis: history of use in archaeology

Links between areas of previous human occupation and increased phosphate content of the surrounding soil were first noted in the late 19th century in surveys of field phosphate levels undertaken for agricultural purposes (Bethell and Máté 1989: 1).  Egyptologist John Hughes noted the same correlation in an archaeological context in Egypt in 1911 (Russell 1957), but no further studies were carried out at that time.   The first systematic use of phosphate analysis for archaeological site identification was successfully performed in Sweden (Arrhenius 1929); the study focused on locating previously unknown archaeological sites through the testing of field topsoils along a large-interval grid.  In the 1930s small-interval phosphate surveys were used in Sweden to attempt to differentiate between different types of settlements based on phosphate patterns (Lorch 1930).  The accuracy and precision of phosphate testing was examined at cemetery sites in the United States of America, Scotland and England in the 1950s (Solecki 1951; Johnson 1956; Biek 1957), where phosphate silhouettes were identified directly corresponding to grave plots. Examination of the deposition and fixation processes of phosphates was also conducted to allow for a more valid interpretation of phosphate concentrations at archaeological sites (Cook and Heizer 1967).   

The first application of a more systematic approach to phosphate analysis in archaeology was performed at the Sutton Hoo burial site in England (Barker et al. 1975), where phosphate analysis was used in an attempt to identify the area where a body may have been, as no body was identified during the excavations.  No specific concentration of phosphates was identified, but the entire burial mound area exhibited general enhancement.  In the 1970s more diverse techniques, such as magnetometry, resistivity and aerial photography, started to be used in conjunction with phosphate analysis to gain a better understanding of buried archaeological features (Sieveking 1973).  Multi-elemental analysis was first used in conjunction with phosphate analysis in the 1980s to gain better insight into what materials were responsible for changes to soil chemistry related to human occupation (Konrad 1983).  Studies in the following years dealt with increasing the reliability and readability of phosphate results through further calibration of testing techniques (Eidt 1984), and the location of anthropogenic phosphates in the soil profile (Craddock 1985).  Phosphate analysis has also been used at cave sites to identify the location of residues on floor surfaces (e.g. Goldberg and Sherwood 2006).

Johanna Ullrich, Ph.D.