The materials and sites are not selected at random, but instead are based on a series of previously defined criteria. These criteria are based on a previously established experimental design, and were chosen according to the initial hypotheses and objectives.

A total of 807 samples have been analysed in this study, consisting of 702 pottery samples from 46 sites, and 105 samples from the C horizons of the soils in these sites (contrasting geological materials)

A total of 77% of the archaeological samples are from sites that belong to a single prehistoric period, while 23% of the samples are from sites with different chronologies (in some cases ranging from the prehistoric period through to the modern day).