Abstract By exploiting the ITC technique sensitivity and versatility, we have studied: 1) The detailed kinetics of nucleation and growth of the occlusions (possibly of Suzuki phase or of its precursors), at the epxense of impurity-vacancy (IV) dipoles, induced by very long annealing at 225° of NaCl samples, moderately doped with Pb and OH− free; 2) The nature of the huge ITC band, which cannot be attributed to point dipole relaxation, but rather to an interfacial ionic polarization, built up at the boundary between the host NaCl matrix and the growing occlusions; 3) The motion parameters of the new ITC band in the frame of the Maxwell-Wagner-Sillars theory. The dielectric measurements were also continuously correlated with optical absorption spectra (taken at ∼10 K), which turned out to be considerably affected by the nucleation process. The results obtained are discussed also in terms of Ostwald ripening and compared with those obtained previously in KCI: Pb system.