Phosphorus in archeological ceramics as evidence of the use of pots for cooking food

Abstract The presence of phosphorus in samples of soil, sediments and water is traditionally considered to be an important indicator of human activity, either archeological or contemporary. Traditionally, the presence of phosphorus in archeological ceramics is attributed to adsorption from the soil subsequent to the discarding of utensils or the presence of the element in the raw material, although a few authors support the hypothesis of the contamination of pots by food during cooking. Given these conflicting views, the present study investigated experimentally the incorporation of phosphorus (and also calcium) into ceramic pots through trials that simulated cooking conditions to verify the potential of the elements as archeological evidence. The material was analyzed using XRD, total chemical analyses, and SEM/SED. The results indicated clearly that both elements were incorporated through the cooking process. The chemical affinity of phosphorus with aluminum makes this element a potentially important archeological record of function. Crystalline phases of the variscite type are formed after 600 h of cooking and depend on the amount of time the pot is in contact with the experimental solution. In contrast, the incorporation of calcium is readily reversible, and the cooking time necessary for the formation of phases is much greater than the working lifespan of a ceramic pot. In other words, calcium cannot be used as archeological evidence of cooking.