Princess Pauline Metternich and the Countess Kielmannsegg duelled topless in 1892. The reason for topless duels was to avoid strips of clothing getting into wounds and causing infection. Nice series of photos!
I've read that sword duelists often fought bare chested so as to limit the likelihood of infection from clothing being thrust into a wound. Don't know how true that is, but would explain topless dueling.