Tattooing involves the placement of pigment into the skin's dermis, the layer of dermal tissue underlying the epidermis. After initial injection, pigment is dispersed throughout a homogenized damaged layer down through the epidermis and upper dermis, in both of which the presence of foreign material activates the immune system's phagocytes to engulf the pigment particles. As healing proceeds, the damaged epidermis flakes away (eliminating surface pigment) while deeper in the skin granulation tissue forms, which is later converted to connective tissue by collagen growth. This mends the upper dermis, where pigment remains trapped within fibroblasts, ultimately concentrating in a layer just below the dermis/epidermis boundary. Its presence there is stable, but in the long term (decades) the pigment tends to migrate deeper into the dermis, accounting for the degraded detail of old tattoos.
Some tribal cultures traditionally created tattoos by cutting designs into the skin and rubbing the resulting wound with ink, ashes or other agents; some cultures continue this practice, which may be an adjunct to scarification. Some cultures create tattooed marks by hand-tapping the ink into the skin using sharpened sticks or animal bones (made like needles) with clay formed disks or, in modern times, needles. Traditional Japanese tattoos (irezumi) are still "hand-poked," that is, the ink is inserted beneath the skin using non-electrical, hand-made and hand held tools with needles of sharpened bamboo or steel. This method is known as tebori.
Traditional Hawaiian hand-tapped tattoos are experiencing a renaissance, after the practice was nearly extinguished in the years following Western contact. The process involves lengthy protocols and prayers and is considered a sacred rite more than an application of artwork. The tattooist chooses the design, rather than the wearer, based on genealogical information. Each design is symbolic of the wearer's personal responsibility and role in the community. Tools are hand-carved from bone or tusk without the use of metal.
The most common method of tattooing in modern times is the electric tattoo machine, which inserts ink into the skin via a single needle or a group of needles that are soldered onto a bar, which is attached to an oscillating unit. The unit rapidly and repeatedly drives the needles in and out of the skin, usually 80 to 150 times a second. This modern procedure is ordinarily sanitary. The needles are single-use needles that come packaged individually. The tattoo artist must wash his or her hands and must also wash the area that will be tattooed. Gloves must be worn at all times and the wound must be wiped frequently with a wet disposable towel of some kind. The equipment must be sterilized in a certified autoclave before and after every use.
Prices for this service vary widely globally and locally, depending on the complexity of the tattoo, the skill and expertise of the artist, the attitude of the customer, the costs of running a business, the economics of supply and demand, etc. The time it takes to get a tattoo is in proportion with its size and complexity. A small one of simple design might take 15 minutes, whereas an elaborate sleeve tattoo or back piece requires multiple sessions that may consist of several hours at a time.
In 1891 the first electric tattoo needle was invented in New York City by modifying Thomas Edison's electric engraving pen. This made the process cheaper and faster; it was taken up by the poor and abandoned by the rich. O'Reilly's machine was based on the rotary technology of the electric engraving device invented by Thomas Edison. Modern tattoo machines use electromagnetic coils. The first coil machine was patented by Thomas Riley in London in 1891, using a single coil. The first twin-coil machine, the predecessor of the modern configuration, was invented by another Englishman, Alfred Charles South of London, in 1899.
Another tattoo machine was developed 1970-1978 by the German tattoo artists Horst Heinrich Streckenbach (1929–2001) and Manfred Kohrs.
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