While most tattoos are lined in black ink, some tattoos, especially portraits, are best done using a powder-shading technique. Shading, as opposed to lining, results in art that looks more realistic. Shading creates a three-dimensional appearance that cannot be captured with art that is simply lined in black and filled with colour.
Many tattoo designs are perfectly suited to a simple outline and colour-fill. Some would even look a bit odd with much shading. The purpose of shading is to create the illusion of depth and form, so designs such as portraits and renderings of organic items, such as flowers, trees and animals, can look interesting and beautiful. By contrast, abstract designs that are meant to be simple might look too busy when shaded.
The needles used for shading are not the same as needles that are used for lining. Using a lining needle to try to do shading can result in very disappointing art. While there are different machines for shading and lining as well, many tattoo artists use the same machine, but different needles. Shader needles are soldered onto a bar that attaches to the machine. There are multiple needles (four, six, seven or nine depending on what the artist needs) on each bar, and they are arranged so that they resemble the teeth of a comb.
The idea of shading is that it makes a piece look three-dimensional with natural-looking shadows and highlights. To achieve this effect, mix ink colours several times to create the gradual change from one colour to another. If the colours aren't mixed, the contrast in colour changes will be too stark. Plan the tattoo thoroughly and mix colours in advance to avoid too many pauses for mixing during the tattooing process.
Many tattoo artists use white ink to create the illusion of highlights, or areas that reflect light more than others. For example, if water is part of the tattoo, the artist can use white ink to make it look like the water is rippling or frothing. This not only creates an interesting illusion of depth, but it can also help ease the transition from one shade of ink to the next. Another technique for creating lighter areas is called a "wash," which involves mixing the ink with sterile water before applying it to skin.