When you look at old photographs or encounter people with tattoos done decades ago in correctional facilities, the first thing that strikes you is their specific color. It’s not the deep charcoal black we’re used to in modern tattoo parlors, but a characteristic grayish-blue or even dirty-blue hue. This visual phenomenon has become so recognizable that in the collective consciousness, the word “nakolka” (tattoo) is inextricably linked with this specific color. But have you ever wondered why this happened? Was it a conscious aesthetic choice or a harsh technical necessity? In this article, as experts from tatufoto.com, we will conduct an in-depth study of the history, chemistry, and physics of the blue pigment in prison tattoos.