Horse chestnuts (in isolation)
No, horse chestnuts for perfumery are not nut nuts; they are what horse folk call the hard hoof-like substance that grows on the horse's lower leg. Why use it in perfumery? Because it embodies the scent we associate with leather so well -- it is highly pungent and animalic, oily and waxy, pervasive, sweaty, and oh, so alluring. I first discovered horse chestnuts during the first year of teaching Natural Botanical Perfumery from one of the students, Pauhla, a horse owner. She had always loved the smell of horses and discovered a creative way to capture the scent of her favorite horse -- by tincturing the clippings from the trimming off of horse chestnuts. She was kind enough to share with everyone and since then, we've all pretty much been hooked on the scent of horse. Horse chestnuts are sourced in a non-cruel manner (it's like clipping fingernails) and has a very high animalic/musky scent intensity, so much so that it must be isolated from all other perfume ingredients else it will invade and conquer, infusing everything in its vicinity with the smell of the barn. It adds a lovely smooth animalic musk to leather accords and one cannot help but think of horses when it is detected.