In the past, inks were made from natural materials. Juices from fruits and vegetables, tannin or gall apples, nuts, soot and tree bark were all commonly used to create a variety of inks and colors. While the term "sepia" is often used to refer to a shade of brown ink, the original sepia ink was made from the ink sacs of certain types of cuttlefish. Natural pigments are still sometimes used today, but chemical dyes are more common and can yield more vivid colors.
The color of ink is generated with pigment or dye. While both are colorful and can be made into many kinds of ink, there are some differences between the two. Dye-based inks are water-soluble, which means that they dissolve in water, whereas pigmented inks do not. The particles in dye are much finer than those in pigment, which makes dye preferred over ink for writing purposes, as dyes will not clog pens as quickly. Dye-based inks also tend to absorb into the fibers of paper much more than pigmented inks.
A solvent or vehicle is the liquid in which a dye or pigment is dissolved or suspended. Linseed oil, soybean oil, water and petroleum distillate are some common solvents for printing inks. However, there are many types of solvents that have a variety of desirable effects. For instance, newspaper ink uses mineral oil as a solvent because this ink is absorbed very quickly into the fibers of a printed newspaper. The viscosity of the solvent is also important; ink for professional mass printing tends to be very thick.
While ink only requires two basic ingredients, the pigment or dye and solvent, there are many additives that used with inks in order to change the properties of the ink. An ink can contain waxes, lubricants, resins and surfactants. It can contain drying agents to make the ink dry faster or humectants to make it dry more slowly. It can also contain fungicides or biocides to prevent organic growth in the wet ink. An ink can also contain additives to change the pH of the ink, which is important in archival inks, which must have a neutral pH. The purpose of the ink determines what additives it may have.