The Nazis tattooed Auschwitz concentration camp inmates with a prisoner number on their left forearm using a hand-held tattooing device. The tattooing process used a metal needle attached to a wooden stick, and the ink used was a mixture of charcoal and water. The tattoos were roughly a half inch tall, and the needle was pushed into the skin and the ink rubbed into the wound. The prisoner number was based on the order in which a prisoner was registered, and it was not related to the person's identity or background. The tattoos were permanent and served as a means of identification for the Nazis and as a way of dehumanizing the prisoners.