„Birch tar oil was used in the eighteenth century alongside civet and castoreum and many other aromatic substances to scent the fine Spanish leather Peau d'Espagne. At the turn of the twentieth century, birch tar has become a specialty fragrance material in perfumery as a base note to impart a leathery, smoky note in fragrances, especially from the leather and tobacco genre, and to a lesser extent in Chypres, especially Cuir de Russieperfumes and fragrance bases, typically together with castoreum and isobutyl quinoline. It is used as an ingredient in some soaps, i.e. the scent of Imperial Leather soap, though other tars (i.e. from pine, coal) with an equally phenolic and smoky odour are more commonly used in soaps as a medicating agent.“

https://en.m.wikipedia.org/wiki/Birch_tar