An ink is a liquid containing various pigments and/or dyes used for coloring a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush or quill. Thicker inks, in paste form, are used extensively in letterpress and lithographic printing.
Ink is a complex medium, comprising solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, fluorescers, and other materials. The components of inks serve many purposes; the ink’s carrier, colorants, and other additives are used to control flow, thickness, and appearance of the ink when dry.
Early varieties include Egyptian ink, various natural dyes made from metals, the husk or outer covering of beans or seeds, and sea creatures like the cuttlefish (known as sepia). India ink is black and originated in Asia. Iron gall ink was used by many of the old masters for drawing. Walnut ink is erroneously thought to have also been used by old masters, however, there is no proof of this. Walnut inks, if they were used, would have faded fairly quickly and would therefore be unsuitable.
Because pigmented inks stay on the surface of paper, less ink is needed to create the same intensity of color as with dye-based inks. Pigmented inks also tend to be more resistant to washing out. For this reason these inks are frequently recommended for applications where erasure is undesirable. Gel inks are particularly resistant to erasure and frequently bear recommendations from forgery experts.
The particle size of the pigment is very important for the ability to diffuse in the solution inks. Qualities such as hue, saturation, and brightness or lightness are inherent in the ink, and vary depending on the source and type of pigment.
To circumvent this problem, dye-based inks are made with solvents that dry rapidly or are used with quick-drying methods of printing, such as blowing hot air on the fresh print. Other methods include harder paper sizing and more specialized paper coatings. The latter is particularly suited to inks used in non-industrial settings (which must conform to tighter toxicity and emission controls), such as inkjet printer inks. Another technique involves coating the paper with a charged coating. If the dye has the opposite charge, it is attracted to and retained by this coating, while the solvent soaks into the paper. Cellulose, the material that paper is made of, is naturally charged, and so a compound that complexes with both the dye and the paper's surface will aid retention at the surface. Such a compound in common use in ink-jet printing inks is polyvinyl pyrrolidone.
An additional advantage of dye-based ink systems is that the dye molecules interact chemically with other ink ingredients. This means that they can benefit more than pigmented ink from optical brighteners and color-enhancing agents designed to increase the intensity and appearance of dyes. Because dyes get their color from the interaction of electrons in their molecules, the way in which the electrons can move is determined by the charge and extent of electron delocalization in the other ink ingredients. The color emerges as a function of the light energy that falls on the dye. Thus, if an optical brightener or color enhancer absorbs light energy and emits it through or with the dye, the appearance changes, as the spectrum of light re-emitted to the observer changes.
A more recent development in dye-based inks are dyes that react with cellulose to permanently color the paper. Such inks are not affected by water, alcohol, and other solvents. As such, their use is recommended to prevent frauds that involve removing signatures, such as check washing. Currently this kind of ink is most often offered for use in fountain pens. The most popular manufacturer of this ink is Noodler.
Approximately 5000 years ago, an ink for blacking the raised surfaces of pictures and texts carved in stone was developed in China. This early ink was a mixture of soot from pine smoke, lamp oil, and gelatin from animal skins and musk. Other early cultures also developed many colors of ink from available berries, plants and minerals.
The India ink used in ancient India since at least the 4th century BC was called masi, which was an admixture of several chemical components. Indian documents written in Kharosthi with ink have been unearthed in Chinese Turkestan. The practice of writing with ink and a sharp pointed needle was common in early South India. Several Jain sutras in India were compiled in ink. In India, the carbon black from which India ink is produced is obtained by burning bones, tar, pitch, and other substances.
About 1,600 years ago, a popular ink recipe was created. The recipe was used for centuries. Iron salts, such as ferrous sulfate (made by treating iron with sulfuric acid), were mixed with tannin from gallnuts (they grow on trees) and a thickener. When first put to paper, this ink is bluish-black. Over time it fades to a dull brown.
Scribes in medieval Europe (about AD 800 to 1500) wrote on sheepskin parchment. One 12th century ink recipe called for hawthorn branches to be cut in the spring and left to dry. Then the bark was pounded from the branches and soaked in water for eight days. The water was boiled until it thickened and turned black. Wine was added during boiling. The ink was poured into special bags and hung in the sun. Once dried, the mixture was mixed with wine and iron salt over a fire to make the final ink.
The reservoir fountain pen dates back to 953, when Ma'ād al-Mu'izz, the caliph of Egypt, demanded a pen which would not stain his hands or clothes, and was provided with a pen which held ink in a reservoir and delivered it to the nib via gravity and capillary action.
In the 15th century, a new type of ink had to be developed in Europe for the printing press by Johannes Gutenberg. Two types of ink were prevalent at the time: the Greek and Roman writing ink (soot, glue, and water) and the 12th century variety composed of ferrous sulfate, gall, gum, and water. Neither of these handwriting inks could adhere to printing surfaces without creating blurs. Eventually an oily, varnish-like ink made of soot, turpentine, and walnut oil was created specifically for the printing press.
Ink refilling services for printer cartridges are offered by large, official printing companies as well as smaller, "unofficial" refill companies. Customers can often cut printing costs by using refill services from a refill company, or buying the new non-OEM brands instead of refilling.
Treatment is a controversial subject. There is no treatment that will undo the damage already caused by the acidic ink. Deterioration can only be stopped or slowed for a period of time. There are some people who think it best not to treat the item at all for fear of the consequences. Others believe that non-aqueous procedures are the best solution. And then, there are some that believe an aqueous procedure may provide the answer for preserving items written with iron gall ink. Aqueous treatments include distilled water at different temperatures, calcium hydroxide, calcium bicarbonate, magnesium carbonate, magnesium bicarbonate, and calcium phytate. There are many possible side effects from these treatments. There can be mechanical damage, which would further weaken the paper. The color of the paper or ink may change and ink may bleed. Other consequences that might arise from aqueous treatment are a change of ink texture or the formation of on the surface of the ink (Reibland & de Groot 1999).
Iron gall inks are generally stored in a stable environment, because fluctuating relative humidity increases the rate at which formic acid, acetic acid and furan derivatives form in the material on which the ink was used. Sulfuric acid acts as a catalyst to cellulose hydrolysis, and iron (II) sulfate acts as a catalyst to cellulose oxidation. These chemical reactions physically weaken the paper, causing brittleness.
The word indelible means cannot be removed or erased. Some types of indelible ink have a very short shelf life because of the solvents used, which evaporate rapidly.
India, Philippines, Indonesia and other developing countries have used indelible in the form of electoral stain to prevent electoral fraud. The Election Commission in India has used indelible ink for many elections. Indonesia used it in their last election in Aceh. In Mali, the ink is applied to the fingernail.