The depth a tattoo needle penetrates is an important factor in how light or dark the finished product appears. Because ink that is injected more deeply affects several layers of the skin, it colors the area more thoroughly.
Tattoo artists should use a needle depth of 1 mm for solid tattoo outlining and lettering. This technique should usually be done with a round liner needle. Artists should use a round shading needle inserted to a depth of .5 mm for tattoo shading.
Experienced tattoo artists develop an eye for seeing whether a customer has thick or thin skin. Adjustments may be necessary according to skin thickness, but these vary from one individual to the next.
While proper needle depth is an important skill for tattoo students to learn, it is not advisable for beginners to practice on human skin. Many times, apprentices practice on grapefruits and artificial skin until they master the technique.