The aim of this poster is to evaluate a new type of leather obtained by organic tannage (synthetic tannins in combination with vegetable tannins). The experiment involved two differently tanned bovine leathers: Leather 1 was tanned with dialdehyde, polymer and mimosa, and Leather 2 with a combination of synthetic, aluminum and mimosa tannins, which has been compared to vegetable tanned leather. The samples were artificially aged and exposed to SO2 and NH3 for different periods of time. The leathers underwent physical and chemical analysis before and after aging. Absorption of water vapors at different exposure times was studied in order to evaluate the leather’s behavior in an atmosphere rich in sulphur dioxide and ammonia. DSC analysis was also carried out. The study concluded that Leather 2 (synthetic/aluminum/mimosa tanned) is suitable for use in the restoration of historical objects. This type of leather has been used in the restoration of three books from the 17th century belonging to the “Moldova” National Museums Complex in Iassy, Romania.