The black texture on the walls is a phenomenon called “The Angels’ Share”. In French “La part des anges” – or in this case, “an angel in waiting”. The black stuff is called “la torule” in French – Baudoinia compniacensis. A black fungus grows upon the doors and walls of a Cognac distillery in Jarnac. The fungus is a habitat colonist with a preference for airborne alcohol (but I prefer to drink it)