Black-and-gray tattoos have become increasingly popular over the last four decades. But many people don't realize that the style has its roots in Chicano art, Catholic imagery and "prison ingenuity." (Yes, they were called Prison-Style tattoos for a reason.) Freddy Negrete, a pioneer in the industry, started tattooing fellow inmates in the early 1970s. And while he's no longer tatting people up with guitar strings and ballpoint pens, he's still using some of the same techniques he mastered back in the day.