This painting depicts the most common method of modern tattooing using the electric tattoo machine, which inserts ink into the skin via a single needle or a group of needles that are soldered onto a bar, which is attached to an oscillating unit. The unit rapidly and repeatedly drives the needles in and out of the skin, usually 80 to 150 times a second. The artist in this image is at the shading stage of the process. Shading simply provides more dimension than line work. It's not the simple, single pass of an outline. Rather, the artist packs ink into the skin repeatedly to create the appearance of shadows and depth.