Inks are found in almost every aspect of human activity. We read newspapers, magazines, and books on a daily basis. We post lists on our refrigerators, jot things down on our calenders, and leave sticky notes for our coworkers and friends. We make piles of photocopies and print lots of pages from our computers. We buy myriad packaged consumer products printed with ink. We use stamps and money, again printed with ink. And if you delve into finding out more about ink, you will learn that people use a lot of ink writing about ink.
What is ink? It is an organic or inorganic pigment or dye dissolved or suspended in a solvent--essentially the same as paint.
The first inks were fruit or vegetable juices; protective secretions from cephalopods such as squid, cuttlefish, and octopus; blood from some types of shellfish; and tannin from galls, nuts, or bark from trees. The first man-made ink appeared in Egypt about 4,500 years ago and was made from animal or vegetable charcoal (lampblack) mixed with glue.
Today's inks are divided into two classes: printing inks and writing inks. Printing inks are further broken down into two subclasses: ink for conventional printing, in which a mechanical plate comes in contact with or transfers an image to the paper or object being printed on; and ink for digital nonimpact printing, which includes ink-jet and electrophotographic technologies.
Color printing inks are made primarily with linseed oil, soybean oil, or a heavy petroleum distillate as the solvent (called the vehicle) combined with organic pigments. The pigments are made up of salts of multiring nitrogen-containing compounds (dyes), such as yellow lake, peacock blue, phthalocyanine green, and diarylide orange. Inorganic pigments also are used in printing inks to a lesser extent. Some examples are chrome green (Cr2O3), Prussian blue (Fe4[Fe(CN)6]3), cadmium yellow (CdS), and molybdate orange (a mix of lead chromate, molybdate, and sulfate).
Black ink is made using carbon black. And white pigments, such as titanium dioxide, are used either by themselves or to adjust characteristics of color inks. Inks also contain additives such as waxes, lubricants, surfactants, and drying agents to aid printing and to impart any desired special characteristics.
Printing ink is a $10 billion global industry. The Census Bureau tracks about 250 printing ink companies in the U.S., which produced 2.2 billion lb of ink with sales of $4 billion.
So what's in the future for ink? Could ink someday become obsolete? The advent of personal computers, personal electronics, and the Internet may one day replace libraries full of printed books and periodicals with electronic products. But the great paperless society hasn't begun to show itself yet, people simply like paper too much. And as long as there's paper, then there will be ink.