Chemical Formula For Ink

 The individual formulas of different types of ink can vary but they all tend to include the same four components: Colorants, vehicles (also known as binders), additives and carrier substances. Once they have been mixed, inks can fall into one of four categories: Aqueous, liquid, paste and powder.

Nowadays, the novelty of filling up a writing pen with ink from an inkwell as died out. Fountain pens are still used but almost always only on formal occasions where neat handwriting and ink is required. The disposable ball point pen has taken over the market because they are cheap to produce, and therefore cheap to buy in bulk unlike fountain pens which can require several expensive refills. Ballpoint pens are also very convenient to use.

The word ink is now most commonly used to describe printer ink in home printing systems. Most homes, schools and businesses now have their own ways of printing which has resulted in printer ink buying becoming a part of daily life, just as purchasing inkwell ink was fifty years ago.

There is an urban legend that states ingesting ink can be harmful to humans, colloquially known as 'ink poisoning'. This is true to a certain extent, as some inks from those in your printer to ink in a ballpoint pen could be hazardous to your health. As you will not be able to know which ink is harmful and which ones aren't, it is best to avoid ingesting ink at all costs. 

 Tattoo Ink Chemistry

 

The short answer to the question is: You can't be 100% certain! Manufacturers of inks and pigments are not required to reveal the contents. A professional who mixes his or her own inks from dry pigments will be most likely to know the composition of the inks. However, the information is proprietary (trade secrets), so you may or may not get answers to questions.
Most tattoo inks technically aren't inks. They are composed of pigments that are suspended in a carrier solution. Contrary to popular belief, pigments usually are not vegetable dyes. Today's pigments primarily are metal salts. However, some pigments are plastics and there are probably some vegetable dyes too. The pigment provides the color of the tattoo. The purpose of the carrier is to disinfect the pigment suspension, keep it evenly mixed, and provide for ease of application.
Tattoos and Toxicity
This article is concerned primarily with the composition of the pigment and carrier molecules. However, there are important health risks associated with tattooing, both from the inherent toxicity of some of the substances involved and unhygienic practices. Some of the risks are described in this article. To learn more about these risks, care of a new tattoo, and get other information, check out some of the sites listed to the right of each page of this article. Also, check out the Material Safety Data Sheet (MSDS) for any pigment or carrier. The MSDS won't be able to identify all chemical reactions or risks associated with chemical interactions within the ink or the skin, but it will give some basic information about each component of the ink. Pigments and tattoo inks are not regulated by the US Food and Drug Administration.
 Tattoo Pigment Chemistry
The oldest pigments came from using ground up minerals and carbon black. Today's pigments include the original mineral pigments, modern industrial organic pigments, a few vegetable-based pigments, and some plastic-based pigments. Allergic reactions, scarring, phototoxic reactions (i.e., reaction from exposure to light, especially sunlight), and other adverse effects are possible with many pigments. The plastic-based pigments are very intensely colored, but many people have reported reactions to them. There are also pigments that glow in the dark or in response to black (ultraviolet) light. These pigments are notoriously risky - some may be safe, but others are radioactive or otherwise toxic.
Here's a table listing the colors of common pigments use in tattoo inks. It isn't exhaustive - pretty much anything that can be used as a pigment has been at some time. Also, many inks mix one or more pigment:

Compostion of Tattoo Pigments
Color	Materials	Comment
Black	Iron Oxide (Fe3O4) Iron Oxide (FeO) Carbon Logwood	Natural black pigment is made from magnetite crystals, powdered jet, wustite, bone black,and amorphous carbon from combustion (soot). Black pigment is commonly made into India ink. Logwood is a heartwood extract from Haematoxylon campechisnum, found in Central America and the West Indies.
Brown	Ochre	Ochre is composed of iron (ferric) oxides mixed with clay. Raw ochre is yellowish. When dehydrated through heating, ochre changes to a reddish color.
Red	Cinnabar (HgS) Cadmium Red (CdSe) Iron Oxide (Fe2O3) Napthol-AS pigment	Iron oxide is also known as common rust. Cinnabar and cadmium pigments are highly toxic. Napthol reds are synthesized from Naptha. Fewer reactions have been reported with naphthol red than the other pigments, but all reds carry risks of allergic or other reactions.
Orange	disazodiarylide and/or disazopyrazolone cadmium seleno-sulfide	The organics are formed from the condensation of 2 monoazo pigment molecules. They are large molecules with good thermal stability and colorfastness.
Flesh	Ochres (iron oxides mixed with clay)
Yellow	Cadmium Yellow (CdS, CdZnS) Ochres Curcuma Yellow Chrome Yellow (PbCrO4, often mixed with PbS) disazodiarylide	Curcuma is derived from plants of the ginger family; aka tumeric or curcurmin. Reactions are commonly associated with yellow pigments, in part because more pigment is needed to achieve a bright color.
Green	Chromium Oxide (Cr2O3), called Casalis Green or Anadomis Green Malachite [Cu2(CO3)(OH)2] Ferrocyanides and Ferricyanides Lead chromate Monoazo pigment Cu/Al phthalocyanine Cu phthalocyanine	The greens often include admixtures, such as potassium ferrocyanide (yellow or red) and ferric ferrocyanide (Prussian Blue)
Blue	Azure Blue Cobalt Blue Cu-phthalocyanine	Blue pigments from minerals include copper (II) carbonate (azurite), sodium aluminum silicate (lapis lazuli), calcium copper silicate (Egyptian Blue), other cobalt aluminum oxides and chromium oxides. The safest blues and greens are copper salts, such as copper pthalocyanine. Copper pthalocyanine pigments have FDA approval for use in infant furniture and toys and contact lenses. The copper-based pigments are considerably safer or more stable than cobalt or ultramarine pigments.
Violet	Manganese Violet (manganese ammonium pyrophosphate) Various aluminum salts Quinacridone Dioxazine/carbazole	Some of the purples, especially the bright magentas, are photoreactive and lose their color after prolonged exposure to light. Dioxazine and carbazole result in the most stable purple pigments.
White	Lead White (Lead Carbonate) Titanium dioxide (TiO2) Barium Sulfate (BaSO4) Zinc Oxide	Some white pigments are derived from anatase or rutile. White pigment may be used alone or to dilute the intensity of other pigments. Titanium oxides are one of the least reactive white pigments.