Ammonium bituminosulfonate (ichthyol or ichthammol, CAS#8029-68-3 ) is a prouct of natural origin obtained in the first step by dry distillation of sulfur-rich oil shale. It is used in medicine as a remedy for treating some forms of skin diseases, such as acne, eczema and psoriasis. It is commonly used in an ointment in 10% or 20% concentrate as a "drawing salve", also called "black ointment". Its dermatological action was discovered by Austrian physician Paul Gerson Unna.