Humans have been using ink for about 5,000 years. The first inks originated in China, but the use of ink quickly spread around the world. Writing in ink on paper or vellum allowed people to send lightweight messages quickly, improving communication. Today there are more kinds of ink than ever, each made from a different combination of ingredients.
Up until the invention of the printing press, most ink fell into one of two categories. The standard writing ink in medieval Europe and well into the 19th century was iron gall ink. This type of ink is made from water and a form of iron called ferrous sulfate. Oak galls, which are growths found on oak trees, are added to make an acidic solution.
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India ink, which dates to the 4th century B.C. or earlier, is made of fine soot mixed with water. Ink-makers then add stabilizing agents to make sure the ink stay on the page. Common stabilizing agents include gelatin, made from animal hooves, or shellac, which is made from a resin secreted by insects.
Modern Writing Inks
Most inks used in modern pens consist of a dye dissolved in a combination of other ingredients, known as the "vehicle" that helps the ink to flow smoothly, bind to the paper, and dry quickly once outside of the pen but not before. Ferrous sulfate is still used, as are gallic and tannic acids derived from oak galls or sumac leaves. Blue inks often contain triphenylmethane, and red inks are based on a dye called eosin. Both are synthesized using a variety of natural resources including benzene and aluminum chloride. Ballpoint and felt-tip pens have led to demand for new solvents, including toluene and propyl alcohol. These solvents are byproducts from coal and oil processing.
The invention of the printing press led to new inks designed for use with presses rather than pens. These mainly use pigments, which sit on top of the paper, rather than dyes, which soak into it. Pigments contain a variety of elements, including copper and titanium. Carbon black is the main black pigment, and it is used in large quantities. The printing ink industry is one of the world's largest consumers of carbon black. Clays are used to add stability to the ink.
Not all inks are used for printing or writing on paper. Tattoo inks are used with a needle to create designs under the skin. Homemade tattoos often use writing ink, but these tend to blur and fade. Like other inks, tattoo inks often contain carbon and iron compounds. Other chemicals used in the pigments can include mercury, lead, cadmium, nickel, chromium, cobalt, and copper. The carrier into which the pigments are mixed is usually based on water or ethyl alcohol.