Terahertz Time-Domain Spectroscopy (THz-TDS), a non-destructuve method in heritage science, was used to analyzed the state of preservation of the Russian icon "Our Lady of Kazan". The study revealed metallic elements in the artwork and signs of previous restoration work, along with a unique paint layer around the faces and necks of the characters in the painting. Additionally, we detected mercury sulfide in specific areas, indicating potential retouches. Despite limited historical information, this investigation holds promise for guiding future restoration work and demostrates the potential of THz-TDS in assesing cultural artifacts.