The business end of your tattoo machine holds the needles. The tattoo needle is often said to inject ink beneath the skin, but this can be misleading. Tattoo needles are not hypodermic needles. They are more like pins, thin metal rods with pointed ends which shove ink beneath the skin. They are almost always used in groups, with different shapes and densities of needle groupings for different purposes. The groups of needles needed for a particular job are soldered onto a bar in the tattoo machine. The machine actually drives the bar, rather than the needles themselves.
There are three major tasks for most tattoos: lining, shading, and filling.
Lining defines the borders of your tattoo art, while shading and filling decorate the inside. These tasks all have their own types of groupings, although shading and filling needle groups are usually interchangeable. The biggest difference between liners and shaders or fillers is needle spacing. Lining tends to be done with a single pass, with the needles moving up and down quickly. Because the needle is moving over any area only one time, the risk of excess damage to the skin is low, and a lot of ink has to be injected quickly. Thus, liner needle groupings are close together. They are almost always arranged in a circle so there is no change in thickness at different angles.
Shaders and Fillers
Shaders and fillers have more variety in their arrangements, with the commonality being that they’re wider-spaced. Shader needles also tend to be run more slowly, allowing for multiple passes with less damage, so the concentration of pigments can be varied and controlled. They can come in rounds, like liners, albeit less closely packed. More commonly, though, they are flats, that is, one or more straight rows of needles. These can be either regular flats with just a single row of needles, two equal rows in a “stacked” arrangement, or magnums which have two or more rows with the rows staggered, and with one row having more needles than the other.
Needles also vary by size, which tend to be chosen by the tattoo style, and taper, which varies by desired depth. Short tapers are essentially less sharp than longer ones. There are just three categories you usually find, long, medium, and short tapers. Longer tapers go deeper than shorter ones. This can be used in addition to, or maybe even instead of, varying the stroke length for different depths. Lining tends to be done more shallowly, while shading is done deeper, and color fills deeper still.
Tattoo needles are often treated as disposable, in which case they must be thrown away in special biohazard containers after use. This is generally the preferred method, and some medical advice says that tattoo clients shouldn’t consent to be tattooed unless new needles are removed from sterile packaging before their very eyes. That said, needles can be reused as long as they are sterilized between uses in an autoclave.