Fields of Study
Printing; photolithography; photography; physics; chemistry; mathematics; calculus; optics; mechanical engineering; material science; graphic design; electromagnetics; microfabrication; semiconductor manufacturing; laser imaging.
Summary
Lithography is an ink-based printing process that was first used in Europe at the end of the eighteenth century. Unlike an older printing press, in which individual pieces of raised type were pressed down onto sheets of paper, lithography uses a flat plate to transfer an image to a sheet of paper. Nearly all books, newspapers, and magazines being published are printed using lithography, as are posters and packing materials. A specialized subfield of lithography known as photolithography is also used in the making of semiconductors for computers. Career opportunities in lithography are growing in specialized areas but overall are neither increasing or decreasing because of the rise of electronic publishing and marketing.
Key Terms and Concepts
emulsion: Mixture of two chemicals; in lithography, often used on plate surfaces.
hydrophilic: Chemical property on a plate’s surface that attracts and holds a water-based ink; the opposite is hydrophobic.
image: Words, pictures, or both on a printing plate.
imagesetter: Device that transfers an image from a computer directly to a plate without the use of photographic negatives.
offset: Transfer of an image from a plate to a secondary surface, often a rubber mat, that reverses it before final printing.
photolithography: Process that uses high-precision equipment and light-sensitive chemicals to make products such as semiconductors.
photomask: Flat surface into which holes have been cut to allow light to pass through; used in photolithography.
Plate: Printing surface, made of metal or stone, on which areas have been chemically treated to attract or repel ink.
Definition and Basic Principles
Lithography is the process of making an image on a flat stone or metal plate and using ink to print the image onto another surface. Areas of the plate are etched or treated chemically in order to attract or repel ink. The ink is then transferred, directly or indirectly, to the surface where the final image appears.
Unlike a process such as letterpress, where raised letters or blocks of type are coated with ink and pressed against a surface such as paper, lithographic printing yields a result that is smooth to the touch. Lithography differs from photocopying in that plates must be created and ink applied before prints can be made. Photocopying uses a process known as xerography, in which a tube-shaped drum charged with light-sensitive material picks up an image directly from a source. Laser printing is another application of xerography and is not the same as lithography.
Photolithography is a process that imitates traditional lithography in several ways but is not identical. Its high level of precision--a photolithographic image can be accurate down to the level of a micrometer or smaller--is useful in applications such as the manufacturing of computer components.
Background and History
Lithography was invented in 1798 by Alois Senefelder, a German playwright. Senefelder, who was looking for a way to publish his plays cheaply, discovered that printing plates could be made by writing on a flat stone block with grease pencil and etching away the stone surface around the writing. Eventually Senefelder developed a process by which ink adhered only to the parts of a flat surface not covered by grease. He later expanded the process to include multiple ink colors and predicted that lithography would one day be advanced enough to reproduce works of fine art.
German and French printers in the early 1800’s made additional innovations. A patent was issued in 1837 to artist Godefroy Engelmann in France for a process he called chromalithography, in which colors were layered to create book illustrations. Interest in lithography and color printing also spread to North America, where printers in Boston invented new technologies that made the mass production of lithographic prints both high quality and economical. The process quickly spread from books to greeting cards, personal and business cards, posters, advertisements, and packaging labels. Lithography is still the leading process by which mass-produced reading material and packaging are printed.
How it Works
Lithography in the context of printing follows a different set of steps than photolithography as used to make microprocessors.
Offset lithography. While there are many ways to print on paper or packaging using lithographic techniques, most items involve a process known as offset lithography. The term “offset” refers to the fact that the printing plate does not touch the paper or item itself.
In offset lithography, a plate is first created with the image to be printed. The plate may be made of metal, paper, or a composite such as polyester or Mylar. Lithographic printing plates were flat at one time, but modern printing presses use plates shaped like cylinders, with the image on the outside. To transfer the image to the plate, the surface of the plate is roughened slightly and covered with a light-sensitive chemical emulsion. A sheet of photo film with a reverse, or negative, of the image is laid over the emulsion. When an ultraviolet light is shone on the negative, the light filters through the image only in the areas where the negative is translucent. The result is a positive image--essentially, a negative of the negative--left on the printing plate.
The plate is treated again with a series of chemicals that make the darker areas of the image more likely to pick up ink, which is oil based. The lighter areas of the image are made to be hydrophilic, or water loving. Because oil and water do not mix, water blocks ink from being absorbed by these areas. A water-based mixture called fountain solution is applied to the surface of the plate and is picked up by the hydrophilic areas of the image. Rollers then coat the plate with ink, which adheres only to the hydrophobic (water-fearing) areas that will appear darker on the final image. Once the plate is inked, the press rolls it against a rubber-covered cylinder known as a blanket. The ink from the plate is transferred to the blanket in the form of a negative image. Excess water from the ink as well as fountain solution is removed in the process. The blanket is rolled against the sheet of paper or other item that will receive the final image. Finally, the paper carrying the newly inked image passes through an oven, followed by a set of water-chilled metal rollers, to set the image and prevent the ink from smudging.
Photolithography. Like lithography, the process of photolithography depends on the making of a plate coated with a light-sensitive substance. The plate is known as the substrate, while the light-sensitive chemical is known as the photoresist. Instead of a photo negative with the image to be printed, a photomask is used to shield the photoresist from light in some areas and expose it in others.
The similarities to traditional lithography end here, however. In photolithography, the substrate—rather than a sheet of paper or packaging material—is the final product. Once the image is transferred through the photo mask onto the photoresist, the substrate is treated with a series of chemicals that engraves the image into the surface. In lithographic printing, the image is never engraved directly onto the plate. Unlike printing plates and blankets, which are cylindrical, substrates are always flat. The result is a thin sheet of silicon, glass, quartz, or a composite etched precisely enough to be used as a microprocessing component.
Maurits (M.C.) Escher was considered a master of lithography. Photo taken around 23 Nov. 1971 by Hans Peters
POPS_Lithography.jpg
Applications and Products
Lithography as a printing technology has developed in multiple, almost opposing, directions throughout its history. Because lithographic plates can be used to make large numbers of impressions, the development of lithography allowed for printing of images and type on a mass scale that was commercially viable, a major change from the letterpress and intaglio methods of printing that came earlier. Over time, lithography came to be associated with lower-cost editions of books and other printed matter intended to be short-lived, such as newspapers, magazines, and catalogs. Lithography has also evolved as a method of artistic printmaking that can produce works of great beauty and high value. On the photolithography side, the technology has kept pace with the needs of generations of computers.
Web-fed offset printing. Large numbers of copies of a printed work--in the range of 50,000 copies and up--require printing processes that can run quickly and efficiently. Web-fed offset printing takes its name from the way in which paper is fed into the press. A web press uses a roll of paper, known as a web, which is printed and later cut into individual sheets. The largest web presses stand nearly three stories tall, print images on both sides of a sheet at once, and can print at a rate of 20,000 copies per hour. Major newspapers and magazines as well as best-selling books with high print runs are printed on web presses. One of the disadvantages of using a web press is that post print options, such as folding and binding, are limited. Page sizes are highly standardized and cannot be changed easily to meet the needs of an individual print run. Image quality also is not as high as that offered by other types of lithographic presses.
Sheet-fed offset printing. As its name suggests, sheet-fed offset printing uses a paper supply of individually cut sheets rather than a paper roll. Each press has a mechanism that feeds paper sheets into the machine, one at a time. This process is less efficient than web-fed printing and can lead to a higher rate of mechanical problems, such as damage to the rubber blanket when more than one sheet is fed into the press in error. However, sheet-fed printing allows for a greater degree of customization for each printing job. The size and type of the paper can be changed, as can the area of the page on which each image is to be printed. A paper of heavier, higher quality grade may be used in a sheet-fed printer. A wider range of post-print options are also available. Sheet-fed print runs can be bound using a number of different methods, including lamination and glue. These features make it more suitable for products such as sales brochures, corporate annual reports, coffee-table books, and posters.
Lithography in art. When it first appeared in the United States in the mid-1800’s, lithography was associated with high-quality printing, particularly reproductions of works of art. The later introduction of technologies such as photogravure printing eventually made lithographic illustrations in mass-produced printed matter obsolete. At the same time, a number of artists on both sides of the Atlantic Ocean were making advances in lithographic printing as an art form. Henri Toulouse-Lautrec depended on lithography to achieve the bold lines and fields of color in his iconic posters for the Moulin Rouge and other French cabarets in the late 1800’s. Another surge of interest in lithography came in the 1920’s with works from painters Wassily Kandinsky, Georges Braque, and Pablo Picasso. In some cases, such as Toulouse-Lautrec’s posters, these works were originally commercial in nature and intended to be reproduced in large print runs. Artists who experimented with lithography in the twentieth century were more likely to be drawn to the medium for its visual characteristics and possibilities for expression, not for its ability to generate copies. Paris was a major center of lithographic art until World War II, at which point many artists relocated to New York. A revival of the technique emerged in the 1950’s with new prints from artists such as Sam Francis, Jasper Johns, and Robert Rauschenberg. Lithography is taught in many fine-arts schools. Some artists prefer to work directly with the stone or metal printing plates, while others draw or paint images and rely on third parties to transfer the work from the page to the plate.
Semiconductor manufacturing. Photolithography has been used to manufacture semiconductors and microprocessing components for about fifty years. When it was first developed, photolithography depended on the use of photomasks that came into direct contact with the photoresist. This contact often damaged the photomasks and made the manufacturing process costly. Next, a system was developed in which photomasks were suspended a few microns above the photoresist without touching it. This strategy reduced damage, but also lowered the precision with which a photomask could project an image. Since the 1970’s manufacturing plants have used a system known as projection printing, in which an image is reflected through an ultrahigh-precision lens onto a photoresist. This technology has allowed manufacturers to fit increasingly higher numbers of integrated circuits onto a single microchip. In 1965, Gordon Moore, a technology executive who would go on to cofound Intel, predicted that the number of transistors that could be placed on a microchip would double about every two years. The prediction has been so accurate that the principle is now known as Moore’s law.
Impact on Industry
Commercial Printing. The market for commercial lithographic printing is a mature one and is not expected to see significant growth in the next several years. Unlike many other areas of technology, lithography in printing does not receive government research funding or have programs at academic institutions devoted to its study.
The commercial printing industry in North America is divided into tiers by company size and niche. As a market, lithographic printing on a large scale is led by RR Donnelley followed by Quad/Graphics. These firms and their competitors dominate market segments such as books, magazines, directories, catalogs, and direct-mail marketing pieces. Beyond corporations such as these, however, the commercial printing industry is made up primarily of small businesses with local clientele. According to the U.S. Bureau of Labor Statistics, seven out of ten companies offering lithographic printing services have fewer than ten employees. Taken as a whole, commercial printers earned about $100 billion in revenue in 2009. The roughly 1,600 daily newspapers in the United States make up another major market segment in lithographic printing. Because most newspapers own and operate their own printing facilities, they are seen as belonging to a related but separate industry, and their revenues are not included in most printing-industry estimates.
Most of the innovations in large-scale lithographic printing that have occurred since the 1990’s involve the use of digital technology. Rather than using film and photo negatives to create reverse images, computers allow typesetters and printers to transfer an image directly onto the surface of a printing plate. However, many developments in commercial printing methods largely involve technologies that do not rely on lithography. When this trend is taken into account, along with the migration of many books and news sources from print formats to electronic ones, the future of commercial lithographic printing seems very limited.
Photolithography. Prospects for photolithography and semiconductor manufacturing are much brighter. The semiconductor industry reported sales worldwide of $298.3 billion in 2010, reflecting a 32 percent increase over 2009. Much of the growth was due to a rise in microchip purchases by customers in the Asia Pacific region, which makes up slightly more than half of the global market by volume. Microchip buyers in this context are not consumers, but rather companies that manufacture computers, mobile phones, and other types of hardware. The leading semiconductor manufacturers also reflect the global nature of this industry. Intel tops the list by volume. Its competitors include Analog Devices, Texas Instruments, and Micron Technology in the United States; STMicroelectronics and NXP Semiconductors in Europe; and, Samsung, Toshiba, NEC Electronics, and Taiwan Semiconductor Manufacturing in Asia.
For many years, industry sources have predicted that photolithography would be replaced by other technologies because of an increasing need for precision in the making of microchips. Innovations such as excimer laser technology have allowed lithography to become so precise that features smaller than a single wavelength of light can be printed accurately. The vast expense of microtechnology on this scale prevents many nonprofit institutions such as universities from devoting significant resources to its study. Instead, advances are most likely to come directly from manufacturing companies themselves, which reinvest about 15 percent of sales into research and development each year. Research funding is also supplied by government sources such as the National Science Foundation, the National Institute of Standards and Technology, the U.S. Department of Energy, and the U.S. Department of Defense.
Careers and Course Work
The course work required for a career in lithography varies widely with the nature of the product and the stage in the printing process.
In traditional lithography, one major professional area is media printing. Books, magazines, and newspapers must be designed and laid out page by page before lithographic plates can be created. Many of the professionals who hold these jobs have earned bachelor’s or master’s degrees in academic areas such as art, graphic design, industrial and product design, and journalism. A background of this type could include course work in typography, color theory, digital imaging, or consumer marketing. Students seeking opportunities in media design also pursue internships with publishers and other companies in their fields of interest.
The mechanical process of lithography has become highly automated. Fewer employees are needed in printing plants than before. Most lithographic press operators receive their training on the job and through apprenticeships. Formal education is offered through postsecondary programs at community colleges, vocational and technical schools, and some universities. Students take courses in mechanical engineering and in the maintenance and repair of heavy equipment. Additional course work may include mathematics, chemistry, physics, and color theory.
Lithography as an artistic printing technique is taught in many college and university art departments. While it is considered too specialized by most institutions for a degree, artists may choose to use lithographic printing to create visual works on paper and other materials.
Photolithography is a highly specialized area of technological manufacturing. Its course work and career track are notably different from those in traditional lithography. Professionals working in photolithography have undergraduate or graduate degrees in fields such as engineering, physics, mathematics, and chemistry. An extensive knowledge of micro-technology and the properties of light-sensitive materials is needed. Because most of the world’s semiconductor manufacturing takes place outside North America, careers in photolithography can involve frequent travel to areas such as Asia.
Social Context and Future Prospects
As a broad category, lithographic printing offers very limited job growth. Consumers are increasingly concerned about the environmental impact of paper use in catalogs and other sources of bulk mail. In an effort to respond to these concerns, many companies have reduced their use of paper-based marketing campaigns. This change has lowered the demand for commercial offset lithography. A similar trend has affected the printing of checks and invoices, which are being replaced by electronic systems and online banking.
The growth of electronic media, from the Internet to handheld e-book readers, has also lowered the need for lithography in the publishing industry. Newspapers are reducing the circulation and length of their paper editions and shifting their publishing efforts to Web sites and news feeds. While the demand for paper-based books is not likely to disappear in the near future, sales of new books in electronic formats are growing at a more rapid pace than their print counterparts. In the print segment, new technology is boosting the use of print-on-demand systems for books, which use digital printing techniques rather than lithography.
Fascinating Facts about Lithography
Commercial lithography changed the way in which companies marketed products to consumers, starting in the late 1800’s. Inexpensive, mass-produced pictures launched the catalog industry. Product advertisements and labels became more vivid and colorful.
Christmas cards printed by L. Prang and Company with images of Santa Claus and evergreen trees first appeared in England in 1873 and in the United States in 1874. Affordable and attractive, the cards were popular instantly and launched the tradition of sending holiday cards to friends and family.
Alois Senefelder, the inventor of lithography, taught himself to write backwards quickly in order to make his first printing plates.
The idea of using a mixture of wax and ink written on stone came to Senefelder by accident. He was interrupted in his work one day by his mother, who needed him to write a bill for a washerwoman waiting at the door. Senefelder scrawled the information onto a new stone printing plate. The result inspired him to develop the process that became lithography.
Senefelder’s first play was called Die Maedchenkenner (The Connoisseur of Girls) . It is believed to have been his only commercial success as a playwright.
In 1846 in Boston, inventor Richard M. Hoe redesigned a lithographic flatbed press by putting the plates onto a rotary drum. The new machine could print six times faster, earning it the nickname “the lightning press.”
The prospects for growth in photolithography are more optimistic. Photolithography continues to be one of the most effective and precise ways to make semiconductors. Until it is replaced by a new technology, the field is expected to keep growing with new demand for smaller, faster computers.
—Julia A. Rosenthal, MS
Further reading
Devon, Marjorie. Tamarind Techniques for Fine Art Lithography . New York: Abrams, 2009. A hands-on manual of techniques for artists seeking to produce lithographic prints, written by the director of the Tamarind Institute of Lithography at the University of New Mexico in Albuquerque. Landis, Stefan, ed. Lithography . Hoboken, N.J.:
Wiley-I STE, 2010. A new detailed textbook on lithography as applied to the design and manufacturing of microtechnology.
Meggs, Philip B., and Alston W. Purvis. Meggs’ History of Graphic Design . 4th ed. Hoboken, N.J.: John Wiley & Sons, 2006. A broad history of graphic design and printing processes throughout the world, including the role of lithography.
Senefelder, Alois. Senefelder on Lithography: The Classic 1819 Treatise . Mineola, N.Y.: Dover Publications, 2005. A reproduction of an essay published nearly two centuries ago by the founder of lithography.
Suzuki, Kazuaki, and Bruce W. Smith, eds. Microlithography: Science and Technology . 2d ed. Boca Raton, Fla.: CRC Press, 2007. A series of essays by several contributors on the processes behind microlithography, one of the manufacturing techniques used to make semiconductors.
Wilson, Daniel G. Lithography Primer . 3d ed. Pittsburgh: GATF Press, 2005. An illustrated overview of each step in the lithographic printing process. Includes chapters on topics such as plate imaging, inks, and papers.