Black and grey tattoos
Black ink was probably first ink available ever. At first, made by side product from burning, now black inks are far more professional and allow deep contrasts. In my opinion, especially last 10 years brought an entirely new quality of black inks.
Shades are achieved in black and grey tattooing on many techniques, the most famous being dilution of ink. But experienced tattoo artist will also use depth of puncture, and hand speed as significant shading factors.
Black and grey tattoos integrate perfectly into human’s skin. Contrary to full-color tattoos, a big portion of the design is made by leaving the untattooed skin. That creates an image in black and skin color.