Although a technology in which seals were first pressed into damp clay tablets is known to have been used by the Babylonians, the Chinese probably invented printing. They used carved stones for making copies by first sprinkling soot over the carving, then placing a piece of paper on it and rubbing until the ashes came off on the stone. The oldest known printings were produced in China 1,200 years ago. They consisted of Buddhist texts, and were made using ink blocks and small pieces of paper.

Around 800 years ago, the Chinese printer Pi Sheng first formed Chinese characters out of bits of clay. He found that by fitting the clay pieces together to spell out words, he could print entire texts. These clay pieces, which would now be called movable type, had the advantage that they could be reused. Later type was made out of wood.

In Korea, pieces of type were placed in a box, or form, so that they spelled out words. By pressing the form against wet sand, the individual pieces created impressions in the sand. Molten metal was then poured over the sand, so that it filled the letter-shaped impressions. When the metal cooled, a solid plate with raised images of the characters was formed. This metal plate was then used to print on paper. The metal plate proved easier to work with than did movable type. While a page was being printed using the metal plate, the original movable type was reassembled to make another plate. This technique is still in use, and is known as type mold. By 1400 AD, Korea had the most advanced printing technology, and even commoners there were able to own copies of official publications.

In Europe, meanwhile, the Romans had not discovered printing, and all books were produced by hand. By about 1000 AD most of these handwritten books had been destroyed, and the few that survived were carried off to the East. Some of the surviving books were later returned to Europe by scholars and priests. There, scribes in monasteries made copies by hand. Each of these handwritten books required many hours of skilled labor to produce, and only the wealthy could afford to own books.

Around 1400, Europeans began to experiment with news ways to make books. They had no knowledge of Chinese printing technologies, and developed methods of printing independently of what was happening on the other side of the world. Some Europeans rediscovered the use of carved blocks, the technology the Chinese had used before they came upon the idea of movable type. But block printing was too slow and expensive to meet the rising demand for books.

The Gutenberg revolution

The first European to successfully use movable type was probably Johann Gutenberg, who was born in Germany in 1397. Gutenberg hit upon the notion of cutting each letter in the alphabet on the end of a small stick. Each letter was then pressed into a small square of metal, and when Gutenberg had a letter-shaped hollow for each letter of the alphabet, he could produce type.

Gutenberg fitted four pieces of wood around the letter-shaped hollow, called a matrix, to form an open box. He then poured molten metal into the box, allowing it fill up the matrix. After the metal had cooled and hardened, the sides of the box were removed, leaving a small block with the letter in relief.

Gutenberg reassembled the box to produce as many copies of each letter as he needed. The walls of the box formed a mold that could be adjusted to fit all letters. This mold made possible the development of a less expensive and faster method of printing than had previously been in use.

By trial and error, Gutenberg discovered that the best metal for his type was a mixture of lead, tin, and antimony. This alloy had the advantage that it did not shrink when cooled, so all letters resembled the original matrix, and the pieces of type could be linked in rows. Alloys of lead, tin, and antimony are still used to make type.

The first book of any note to be printed with movable type was Gutenberg’s Bible, published in 1456. Copies are still in existence. Printed in Latin, its pages consist of two columns of type, each 42 lines long. It is 1282 pages long. In producing this book, the type was arranged on each page, and inked before the paper was pressed down on it. Gutenberg may have used a wine press fitted with a heavy screw to press the paper against the type. After removing the sheet of paper, the type would then have been re-inked before another sheet of paper was placed on it.

Gutenberg printed about 200 Bibles in a five-year period. Each of the printed characters in the Bible was made to resemble handwriting. Because the type in the Gutenberg Bible makes the printed page very dark, it is called black letter. Gutenberg’s Bible has wide margins, and the pages are well designed.

Gutenberg died in poverty. But his invention rapidly spread to other countries in Europe. By the time that Columbus was setting off for the New World, around 14,000 separate books had been printed in Europe. As hundreds of copies of each of these books could be found, there may have been as many as 20 million books in Europe at the time.

European printers continued to experiment with Gutenberg’s technology. To make printed type easier to read, the Frenchman Nicolas Jensen introduced serifs, or tiny tails, at the end of his letters. This innovation had the effect of causing the reader’s eye to skip from one letter to the next. This type eventually became more popular than Gutenberg’s black letter type, and the letters are now known as Roman-style letters, because they were designed to resemble the stone carvings in ancient Rome.

Aldus Manutius designed a narrow slanting type, now called italic in honor of Italy where Manutius lived. This enabled Manutius to place many words on a single page, and small, cheap books soon became readily available.

The early European printers arranged their type by hand, character by character in a process known as typesetting. Type was stored in cabinet drawers, called cases. Each case held a complete set of type in a particular style and size, called a font. It was the convention for printers to keep their capital letters, now referred to as upper-case letters, separate from their small, or lower-case, letters.

Letters were removed from the type case, and arranged in rows in a small metal tray. Space bars were inserted to adjust the width of the line. Filling out a line became known as justification.

When the metal tray had been filled with justified lines, the lines were transferred to a larger metal tray called a galley. The galley was inked when the printer had made sure that there were no mistakes in the set type. The printed sheet of paper that was produced became known as the galley proof.

At first, European printers traveled from town to town, taking their type and small hand-operated presses with them. They became known as journeyman printers. Later, when plenty of shops had been established where they could practice their trade, itinerant printers traveled about with only their skills.

Conventional printing methods

Conventional typesetting machines mold type from molten metal, in a process called type casting, for each new printing job. Casting type is more efficient than setting type by hand. Cast type can be melted down, and reused. Typesetting machines either cast an entire line of type at once (linotype machines) or a single letter at a time (monotype machines).

James O. Clephane and Ottmar Merganthaler developed the first commercially successful linotype machine in 1886. Their machine cast type five times faster than an individual could set type.

The linotype machine was operated by a compositor. This individual worked in front of a keyboard. The keyboard consists of separate keys for each letter, number, or punctuation mark found in a case of type. The text to be set, called the copy, was placed above the keyboard. The compositor keyed in the text, character by character. Each time a key was touched, a small letter matrix dropped into a slot.

When the compositor filled in the first line of type, he sent it to a mold. Molten metal was then forced into the mold to produce a metal bar with a whole line of letters in relief. This cast line was then dropped down into the galley, and the process is continued until all the copy had been set.

The advantages of monotype begin to show up with reference works and scientific publications, where complicated tables, punctuation, and figures may have to be inserted. With monotype, corrections can be made by hand without resetting the entire line.

Letterpress

Letterpress printing is an example of relief printing, the process in which printing ink is transferred to a printed surface from areas that are higher than the rest of the printing block. In the case of letterpress printing, each page of type is used as the mold for a papiermache mat, which is actually a copy in reverse of that page of type. The mold in turn is used to make a metal copy of the entire page, and this metal copy is used for printing. This was the traditional way to print newspapers. Variations of this printing technique may use plastic or rubber plates. Because several plates can be made from each original, brand new type can be introduced at regular intervals, ensuring that copies remain sharp and clear.

Large presses

In rotary presses, the plates are fastened around cylinders. These cylinders continuously turn against an endless conveyance of moving paper, printing the paper sheet as it moves past. The sheet can be printed on both sides, cut, folded, and tied up so that it comes out as stacks of finished newspaper. Fabrics are also printed on large machines in which cylinders turn against the cloth, printing colored designs on it.

In the case of cylinder presses, a flat type bed slides back and forth beneath a turning cylinder to which a paper sheet is attached. Grippers hold the sheet of paper in place against the turning cylinder before releasing it, and picking up another sheet.

Printing pictures

Images are still occasionally printed using metal plates that are engraved or etched by hand. In the case of photoengraving, a similar process makes use of a camera. First, the image is photographed to produce a negative on a sheet of transparent film. The negative is then used to print the image on a sheet of zinc that is covered with a gelatin-like substance, or emulsion. Chemicals in the emulsion transfer the image to the zinc sheet. The zinc sheet is then treated with chemicals that etch the metal surface except where the image appears. The image remains elevated above the etched surface, and the plate is used to print the image on paper.

Black and white photographs with many shades of gray have been traditionally handled by a process called halftone engraving. With this technique, the original picture is first photographed. Then a screen in the camera is used to break up the picture into thousands of tiny squares. The negative consists of thousands of tiny dots, one for each square. The photoengraving from this negative has many tiny dots raised in relief above the eaten-away metal surface. Portions of the plate that will appear as dark areas in the finished picture are covered with relatively large dots. The portions of the plate that will appear gray are covered with smaller dots. And the portions that will print white are covered by dots that may appear invisible to the naked eye.

Ordinary newspaper pictures are produced with screens of about 5,000 dots per square inch (or about 70 dots per linear inch). A very fine-screened engraving, such as might appear in art books and magazines, might use up to 18,000 dots per square inch (or about 135 dots per linear inch).

Color printing requires plates for each color. Most color pictures can be printed using four plates, one for black and one each for red, blue, and yellow.

Photogravure

In photogravure, ink is held in the hollows of a plate rather than on high relief. This method of printing is known as intaglio. The photogravure plate, like the halftone plate, is produced with the aid of a camera and an acid to etch away parts of the metal plate. The acid creates hollows of different depths. The deepest hollows hold the most ink and print the darkest areas in the picture. Shallow hollows hold less ink and print lighter areas.

Lithography

In lithography, a picture is drawn on a smooth flat stone with a special type of oily crayon. Because the printing surface is flat, lithography is an example of planographic or surface printing. Then the lithographer passes a water-soaked roller over the stone. The water adheres to the bare stone surface, but does not stick to the oily crayon marks. Another roller soaked with printer’s ink is passed over the stone. Since the ink will not mix with water, it cannot stick to the wet stone, but does stick to the oily crayon marks. When a sheet of paper is pressed against the inked stone, the paper takes up ink only from the places where the crayon lines are. This produces a print of the original drawing on paper.

Photolithography is a variation of lithography performed by machine and using a camera. In this case, a zinc plate is used instead of the stone. The picture is placed on the plate by photographic means rather than by hand. Characters and words can also be printed on the plate. The zinc plate is then curved around the printing cylinder. As the cylinder turns, the plate first presses against a wet roller, and then against an ink roller. This has the effect of covering the blackened portions of the plate with ink. The inked plate next rolls against a rubber-blanketed cylinder so that the image is picked up. The blanketed cylinder then transfers the image to the paper. This kind of printing is known as offset printing.

Phototypesetting

Rather than using hollowed-out metal plates, phototypesetting machines use strips of photographic film to carry images of the text that will be printed. The phototypesetting machine produces images on fresh, unexposed film. Conventional phototypesetters can expose up to 50 characters per second, but usually expose closer to 30 characters per second. Phototypesetting does not use hot metal. Instead, type is set by exposing a light-sensitive material (film or paper) to light projected through a character negative. A computer controls timing.

Another revolution

In the early 1980s the personal computer made its first appearance in many homes and businesses. A panoply of software applications followed suit, and before long the era of desktop publishing began. The first desktop publishing systems consisted of a personal computer and a dot-matrix or daisy wheel printer. With the introduction of the laser printer in 1985, desktop publishing was well advanced.

Recent advances in on-line document delivery systems, many incorporating multimedia techniques, have led some to suggest that we are in the midst of a revolution in publishing that will eventually prove to be as far reaching as the revolution that Gutenberg’s printing press set in progress over 500 years ago.

Desktop publishing

In desktop publishing, text is first prepared on a word processor, and illustrations are prepared using drawing software. Photographs or other art may also be captured electronically using a scanner. The electronic files are next sent to a computer running a page-layout application. Page layout software is the heart of desktop publishing. This software allows the desktop publisher to manipulate text and illustrations on a page.

KEY TERMS

Case— A shallow tray divided into compartments to hold fonts of different types. The case is usually arranged in a set of two, the upper case for capital letters and the lower case for small letters.

Desktop publishing— The writing, assembling, design, and printing of publications using microcomputers. Depending upon the printing quality desired, the electronic pages may either be printed on a desktop printer, or sent to a printing bureau where the electronic document is loaded onto a highend computer.

Font— A complete set of type in a particular style and size.

Galley— A metal tray filled with lines of set type.

Galley proof— A copy of the lines of type in a galley made before the material has been set up in pages. The galley proof is usually printed as a single column of type with wide margins for marking corrections.

Intaglio printing— The process of printing in which the design or text is engraved into the surface of a plate so that when the ink is wiped off, ink remains in the grooves and is transferred to paper in printing. Photogravure is a type of intaglio printing.

Justification— Filling out a line of type with space bars to a specified length.

Linotype— Typecasting machine which casts a whole line of type at once.

Monotype— Typecasting machine which casts single letters.

Planographic printing— The process of printing from a flat surface, also known as surface printing. Lithography and photolithography are two examples of planographic printing.

Relief printing— The process of printing from letters or type in which the printing ink is transferred to the printed surface from areas that are higher than the rest of the block. Letterpress printing is an example of relief printing.

Depending upon the printing quality desired, the electronic pages may either be printed on a desktop printer, or sent to a printing bureau where the electronic document is loaded onto a high-end computer. If the document is sent to a printing bureau, the scanned images may be replaced with higher-resolution electronic images before printing.

If the document is to be produced in color, the printing bureau will use color separation software to produce four electronic documents, each representing the amount of cyan, magenta, yellow, and black that go on one page. The color separation process produces four full-sized transparent negatives. When these negatives are superposed, they produce an accurate grayscale negative of the whole page.

Flexible plates are then made from the four negatives, with one ink color per plate. Clear areas on the film end up a solid raised areas on the plate. In this case, all of the color is printed on the paper. Gray areas, which become regions of raised dots on the plate, put down limited amounts of ink on the paper. Black areas produce no raised areas, so the paper remains white. The plates are then attached to four rollers, one for each color. As the paper passes under each of the rollers, it gets a coat of one of the four colors.

Most desktop printers create images by drawing dots on paper. The standard printer resolution is 300 dots per inch, but higher resolutions are available. This is much higher than the computer terminal’s resolution of 72 dots per inch.

Dot-matrix printers

Dot-matrix printers work by drawing dots in much the same way that typewriters produce characters. They create whole letters by striking a sheet of paper through an inked ribbon. The dot matrix printer is ideally suited for printing carbon-copy forms, but does not find much current use in desktop publishing.

Laser printers

Laser printers currently accommodate the high volume printing needs of many large organizations, and meet the more modest requirements of individuals and small businesses. In laser printing, electronic signals describing the document are first sent from the desktop publishing computer to the printer’s logic board. Printing fonts are next loaded into the printer’s memory. The printer’s central processing unit then sends light signal instructions to a laser, which focuses a beam of light on a rotating drum in the printer. This beam is turned on where black dots will appear, and turned off where the page will remain white.

The rotating drum is coated with a negatively charged, light sensitive material that becomes positively charged wherever the light strikes it. Negatively charged toner particles are attracted to positively charged regions on the drum. This creates the image to be printed on the drum.

A sheet of paper is drawn from the printer’s paper tray so that it passes between the drum and a positively charged wire. The positively charged wire draws the negatively charged toner particles from the drum to the paper. Finally, the toner is bonded to the paper as it passes through two rollers that are heated to about 320°F (160°C).

Ink jet printers

Ink jet printers offer low cost printing alternatives to laser printers, while retaining some of the print quality of laser printers. They operate silently, are lightweight, and make good home printers.

In ink jet printing, liquid ink is pumped into a set of chambers, each containing a heating element. There the ink is heated until it vaporizes. The vaporous ink is then forced through tiny nozzles, squirting dots on the paper. As each line of text is written, the paper advances slightly to accept another line.