According to Tracy V. Wilson of How Stuff Works, tattoos are done by an artist injecting ink into a person's skin using an electrically powered tattoo machine. The machine uses a small needle to puncture the skin between 50 to 3,000 times per minute and penetrates the skin by about a millimeter to deposit drops of insoluble ink into the dermis, the second layer of the skin.
The tattoo machine was invented by Samuel O'Reilly in the late 1800s, according to Wilson. O'Reilly modified Thomas Edison's autographic printer, which engraved hard surfaces, to engrave skin. Modern tattoo machines include a sterilized needle, a tube system for drawing the ink through the machine, an electric motor and a foot pedal, which controls the vertical movement of the needle.
Wilson explains the procedure tattoo artists follow before using a tattoo machine to apply a tattoo. First, they wash and inspect their hands. They then disinfect their work area, place plastic bags on spray bottles and make sure all equipment is sterilized so the client and artist do not contract an infection or disease. The tattoo artist explains the sterilization process to the client, removes all equipment from the sterilized packaging and disinfects the client's skin with a mixture of water and antiseptic soap. The artist is then ready to apply a tattoo design previously decided upon by the client.