Sigillography is the science that studies the manifold aspects of the seals. A seal can be defined as an imprint obtained on a malleable medium by imprinting an incised matrix, which transfers on it the characteristic signs of a person or an institution. We use THz spectroscopy and imaging for non-destructive evaluation of natural materials within old seals. Using a time domain THz spectroscopy and imaging system, THz transmission images are generated in the 0.1–3 THz range and demonstrate that the spectral properties of these materials allow to see across and under a thick layer of old materials.