Ink

• 1. Introduction

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  Ink is a gel, a sol, or a solution carrying at least one colorant, a dye or a pigment, used to color a surface and produce text, an image, or a design. It moves through a pen, a brush, a reed pen, or a quill. In paste form, thicker versions feed letterpress and lithographic printing. Behind that simple description sits a surprisingly crowded recipe. A single ink can hold solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, fluorescents, and more. Each ingredient pulls its weight, shaping how the ink flows, how thick it sits, and how it looks once dry. So how did so many cultures arrive at this fluid independently? Why does some ink eat the very paper it was meant to preserve? And how did a childhood hobby of dripping ink onto paper end up inside a psychological test? The answers begin with soot and fire.

• 2. Independent Origins

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  Lampblack, a kind of soot collected as a by-product of fire, is believed to lie behind the earliest inks from every civilization. Many ancient cultures around the world discovered and formulated inks on their own, driven by the simple need to write and draw. What we know comes from two sources: archaeological analyses, and written texts that survived on their own ink.

  Ancient Egypt used ink for writing and drawing on papyrus from at least the 26th century BC. Egyptian red and black inks carried iron and ocher as pigments, along with phosphate, sulfate, chloride, and carboxylate ions, and lead served as a drier.

  China's earliest inks may reach back four millennia, to the Chinese Neolithic Period. These drew on plant, animal, and mineral materials such as graphite, ground with water and applied with ink brushes. Direct evidence for the earliest Chinese inks, resembling modern inksticks, appears around 256 BC at the end of the Warring States period, made from soot and animal glue. The finest inks for drawing or painting on paper or silk come from the resin of pine trees between 50 and 100 years old. The Chinese inkstick uses a fish glue, while Japanese glue, called nikawa, comes from cow or stag.

• 3. India Ink And The East

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  India ink was invented in China, even though its materials were often traded from India, which is how it got its name. The traditional Chinese method ground a mixture of hide glue, carbon black, lampblack, and bone black pigment with a pestle and mortar, then poured it into a ceramic dish to dry. To use the dry cake, a wet brush reliquified it.

  The Cao Wei dynasty, which ran from 220 to 265 AD, saw the manufacture of India ink well established. Indian documents written in Kharosthi with ink have been unearthed in Xinjiang. Writing with ink and a sharp pointed needle was common in early South India. Several Buddhist and Jain sutras in India were compiled in ink, carrying scripture forward in a medium that began with soot and glue.

• 4. European Recipes

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  Cephalopod ink, known as sepia, shifts from dark blue-black to brown as it dries, and served as an ink in the Graeco-Roman period and after. Black atramentum also saw use in ancient Rome. Sharon J. Huntington, writing for The Christian Science Monitor, describes a recipe created about 1,600 years ago and used for centuries: iron salts such as ferrous sulfate, made by treating iron with sulfuric acid, mixed with tannin from gallnuts and a thickener. Fresh on paper it looks bluish-black, then fades over time to a dull brown.

  Scribes in medieval Europe, from about AD 800 to 1500, wrote mainly on parchment or vellum. One 12th century recipe asked for hawthorn branches cut in spring and left to dry. The bark was pounded off and soaked in water for eight days, then the water was boiled until it thickened and turned black, with wine added during boiling. The mixture went into special bags hung in the sun, then was combined again with wine and iron salt over a fire to make the final ink.

  The caliph of Egypt, Ma'ad al-Mu'izz, demanded in 953 a pen that would not stain his hands or clothes. He received a pen that held ink in a reservoir, possibly the first fountain pen. Centuries later, in the 15th century, Johannes Gutenberg needed a wholly new ink for his printing press. According to Martyn Lyons in Books: A Living History, Gutenberg's dye was indelible, oil-based, and made from lamp-black mixed with varnish and egg white. The handwriting inks of the day, the Greek and Roman blend of soot, glue, and water, and the 12th century mix of ferrous sulfate, gall, gum, and water, blurred on printing surfaces. An oily, varnish-like ink of soot, turpentine, and walnut oil solved the problem.

• 5. Pigments Versus Dyes

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  Pigments are solid, opaque particles suspended in ink, and they get used more often than dyes because they are more color-fast. They cost more, run less consistent in color, and offer a narrower color range. Pigment molecules typically link into crystalline structures 0.1 to 2 micrometers in size, making up 5 to 30 percent of the ink volume. Solvent-based inks suit high-speed printing and applications that need quick drying, and adding TiO2 powder gives superior coverage and vibrant colors.

  Dye-based inks run much stronger than pigment-based ones, producing more color of a given density per unit of mass. Because dyes dissolve into the liquid phase, they tend to soak into paper and can bleed at the edges of an image. Makers fight this with fast-drying solvents, with blowing hot air on fresh prints, with harder paper sizing, and with specialized coatings. One approach coats the paper with a charge, so an oppositely charged dye is pulled to the surface while the solvent sinks in. Cellulose, the wood-derived material in most paper, is naturally charged, and a compound that binds both dye and surface helps retention; such a compound is common in inkjet inks.

  Dye molecules can interact with other ink ingredients, drawing extra benefit from optical brighteners and color-enhancing agents. These inks serve anti-counterfeit purposes and appear in some gel inks, fountain pen inks, and paper currency, reacting with cellulose to produce a permanent color change. Dye-based inks even color hair. A separate class, functional colorants, goes further than absorption, adding fluorescence, phosphorescence, thermochromism, and photochromism. Built from microencapsulated dyes, rare-earth phosphors, or polymer-based nanoparticles, they change appearance in response to light or temperature, which makes them useful in security printing and smart packaging.

• 6. What Ink Does To Paper

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  Carbon inks were commonly made from lampblack or soot with a binding agent such as gum arabic or animal glue, which keeps the carbon particles suspended and stuck to paper. Those particles do not fade over time, even under bleach or sunlight, and the ink stays chemically stable without harming the paper's strength. The catch is preservation: carbon ink smudges in humid environments and can wash off surfaces, so a dry environment is the best way to keep a carbon-ink document, as Barrow noted in 1972. More recently, carbon inks made from carbon nanotubes have been created, suspending the nanotubes in a polymer and printing electrically conductive patterns through inkjet printers.

  Iron gall ink became prominent in the early 12th century and was long thought the best ink available, yet it is corrosive and damages paper over time, a point Waters made in 1940. Items written with it turn brittle, and the writing fades to brown. The original scores of Johann Sebastian Bach are threatened by this very property. The German State Library holds the majority of his works, and about 25 percent of those are in advanced stages of decay. Corrosion comes from acid-catalyzed hydrolysis and iron(II)-catalysed oxidation of cellulose, with sulfuric acid speeding hydrolysis and iron(II) sulfate speeding oxidation.

  Treatment for preserving iron gall ink remains a controversial subject, because no treatment undoes damage already done; deterioration can only be stopped or slowed. Some argue for leaving items untouched, some favor non-aqueous procedures, and others trust aqueous ones using distilled water at various temperatures, calcium hydroxide, calcium bicarbonate, magnesium carbonate, magnesium bicarbonate, or calcium hyphenate. Each carries side effects, from mechanical damage to color change, ink bleed, altered texture, or plaque on the ink's surface. Stable storage matters too, since fluctuating relative humidity raises the rate at which formic acid, acetic acid, and furan derivatives form in the material.

• 7. Toxicity And Environment

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  Ink is often assumed to be non-toxic even if swallowed, and that is a misconception. Once ingested, ink can be hazardous, including the kind in digital printers and even in a common pen. Death is unlikely, but repeated skin contact or ingestion can bring severe headaches, skin irritation, or nervous system damage, traced to solvents or to pigment ingredients such as p-Anisidine, which helps create some inks' color and shine.

  Three environmental issues stand out: heavy metals, non-renewable oils, and volatile organic compounds. Some regulatory bodies have set standards for the amount of heavy metals in ink. Recent years have brought a trend toward vegetable oils rather than petroleum oils, answering demand for better environmental sustainability and easing the drain on the non-renewable oils and metals that ink consumes.

• 8. Indelible Marks And Inkblots

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  Indelible means un-removable, and some indelible inks have a very short shelf life because their solvents evaporate so quickly. India, Mexico, Indonesia, Malaysia, and other developing countries have used indelible ink as an electoral stain to prevent electoral fraud. Election ink based on silver nitrate was first applied in the 1962 Indian general election, after being developed at the National Physical Laboratory of India.

  The election commission in India has relied on indelible ink across many elections, and Indonesia used it in its 2014 election; in Mali the ink goes on the fingernail. The method is not infallible. It can be turned to fraud by marking opponents before they vote, and there are reports of indelible ink washing off voters' fingers in Afghanistan.

  Justinus Kerner, a 19th century German poet, invented the art of klecksography, making images from inkblots, the German Tinten-Klecks, and in 1857 he published a book of klecksographs and poetry titled Klecksographien. A similar book, Gobolinks, or Shadow-Pictures for Young and Old, appeared in the United States in 1896. In his childhood Hermann Rorschach kept a klecksography hobby, and that pastime eventually grew into his Rorschach test, where ink poured onto paper became a window into the mind.