Two-dimensional longitudinal and transverse relaxation time correlation as a low-resolution nuclear magnetic resonance characterization of ancient ceramics

Longitudinal and transverse relaxation time correlation (T-1-T-2) is employed as a nuclear magnetic resonance noninvasive characterization tool for archeological ceramics. This paper is aimed at investigating whether the most relevant firing-induced changes in ceramics, including those involving pore space properties and paramagnetic mineral structures, could be used as markers of the firing process and therefore of ceramics themselves. Ancient ceramics are made up of naturally available clays, often rich in iron impurities, which undergo relevant modifications of pore distribution upon firing. The firing process also assists chemical and physical rearrangement of iron-bearing species, yielding mineral structures with different magnetic properties. That being so, T-1-T-2 maps are expected to show the interdependence between ceramic structure and firing technology. T-1 and T-2 distributions are basically proportional to pore-size distribution, but T-2, which is also sensitive to magnetic susceptibility effects, may give information on the porous matrix composition as well. Such a methodology has first been employed on laboratory-prepared ceramic samples, with different paramagnetic compositions and controlled firing temperatures, in order to tackle the problem of model-ceramic selection. Then, the T-1-T-2 correlation approach has been used on medieval ceramic findings in order to get information about their thermal and compositional history. The information obtained by means of two-dimensional correlation maps proves coherent with archeological dating, thus illustrating the capabilities of this method.