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Tattoo inks are available in a range of colors that can be thinned or mixed together to produce other colors and shades. Most professional tattoo artists purchase inks pre-made (known as pre-dispersed inks), while some tattooers mix their own using a dry pigment and a carrier.
Tattoo ink is generally permanent. Tattoo removal is difficult, painful, and the degree of success depends on the materials used. Recently developed inks claim to be comparatively easy to remove. Unsubstantiated claims have been made that some inks fade over time, yielding a "semi-permanent tattoo."
In the United States, tattoo inks are subject to regulation by the U.S. Food and Drug Administration as cosmetics and color additives. The FDA and medical practitioners have noted that many ink pigments used in tattoos are “industrial strength colors suitable for printers’ ink or automobile paint.”
In California, Proposition 65 requires that Californians be warned before exposure to certain harmful chemicals; tattoo parlors in California must warn their patrons that tattoo inks contain heavy metals known to cause cancer, birth defects, and other reproductive harm.
Manufacturers are not required to reveal their ingredients or conduct trials, and recipes may be proprietary. Professional inks may be made from iron oxides (rust), metal salts, plastics. Homemade or traditional tattoo inks may be made from pen ink, soot, dirt, blood, or other ingredients.
Heavy metals used for colors include mercury (red); lead (yellow, green, white); cadmium (red, orange, yellow); nickel (black); zinc (yellow, white); chromium (green); cobalt (blue); aluminium (green, violet); titanium (white); copper (blue, green); iron (brown, red, black); and barium (white). Metal oxides used include ferrocyanide and ferricyanide (yellow, red, green, blue). Organic chemicals used include azo-chemicals (orange, brown, yellow, green, violet) and naptha-derived chemicals (red). Carbon (soot or ash) is also used for black. Other elements used as pigments include antimony, arsenic, beryllium, calcium, lithium, selenium, and sulphur.
Tattoo ink manufacturers typically blend the heavy metal pigments and/or use lightening agents (such as lead or titanium) to reduce production costs.
A carrier acts as a solvent for the pigment, to “carry” the pigment from the point of needle trauma to the surrounding dermis. Carriers keep the ink evenly mixed and free from pathogens, and aid application. The most typical solvent is ethyl alcohol or water, but denatured alcohols, methanol, rubbing alcohol, propylene glycol, and glycerine are also used. When an alcohol is used as part of the carrier base in tattoo ink or to disinfect the skin before application of the tattoo, it increases the skin's permeability, helping to transport more chemicals into the bloodstream.
A variety of medical problems, though uncommon, can result from tattooing.
Medical workers have observed rare but severe medical complications from tattoo pigments in the body, and have noted that people acquiring tattoos rarely assess health risks prior to receiving their tattoos.
A recent case report also showed that tattoo pigment migrate into lymph nodes. These can show up on some types of medical scans as tumors. One woman was given a complete hysterectomy only to find out later that the lymph nodes contained tattoo pigment. ref: Case Report: Extensive Tattoos Mimicking Lymphatic Metastasis on Positron Emission Tomography Scan in a Patient With Cervical Cancer, Narine Grove, MD, Ma Zheng, MD, Robert E. Bristow, MD, and Ramez N. Eskander, MD. Obstetrics & Gynecology, 2015;0:1-4 DOI: 10.1097/AOG.0000000000000701
Other tattoo inks
Glow in the dark ink and blacklight ink
Both blacklight and glow in the dark inks have been used for tattooing. Glow in the dark ink absorbs and retains light, and then glows in darkened conditions by process of phosphorescence. Blacklight ink does not glow in the dark, but reacts to non-visible UV light, producing a visible glow by fluorescence. The resulting glow of both these inks is highly variable. The safety of such inks for use on humans is widely debated in the tattoo community.
The ingredients in some "glow" inks are listed as: (PMMA) Polymethylmethacrylate 97.5% and microspheres of fluorescent dye 2.5% suspended in UV sterilized, distilled water.
Removable tattoo ink
While tattoo ink is generally very painful and laborious to remove, tattoo removal being quite involved, a recently introduced ink has been developed to be easier to remove by laser treatments than traditional inks.
Health Canada has advised against the use of "black henna" temporary tattoo ink which contains para-phenylenediamine (PPD), an ingredient in hair dyes. Black henna is normally applied externally in temporary Mehandi applications, rather than being inserted beneath the skin in a permanent tattoo.
Allergic reactions to PPD include rashes, contact dermatitis, itching, blisters, open sores, scarring and other potentially harmful effects.
Ancient Roman recipe
The Roman physician Aetius created a recipe for tattoo ink: 
One pound of Egyptian pine bark
Two ounces of gall (insect egg deposits)
One ounce of vitriol (iron sulphate)
Mix well and sift. Soak powder in 2 parts water and 1 part leek juice. Wash the skin to be tattooed with leek juice. Prick design with needles until blood is drawn. Rub in the ink.
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