Photoengraving

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Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that shields some areas during a subsequent operation which etches, dissolves, or otherwise removes some or all of the material from the unshielded areas. Normally applied to metal, it can also be used on glass, plastic and other materials.

Photoresist light-sensitive material used in photolithography and photoengraving

A photoresist is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry.

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A photoresist is selected which is resistant to the particular acid or other etching compound to be used. It may be a liquid applied by brushing, spraying, pouring or other means and then allowed to set, or it may come in sheet form and be applied by laminating. It is then exposed to light—usually strong ultraviolet (UV) light—through a photographic, mechanically printed, or manually created image or pattern on transparent film. Alternatively, a lens may be used to project an image directly onto it. Typically, the photoresist is hardened where it receives sufficient exposure to light, but some photoresists are initially hard and are then softened by exposure. A solvent is used to wash away the soft parts, laying bare the underlying material, which is then bathed in or sprayed with the acid or other etchant. The remaining photoresist is usually removed after the operation is complete.

Acid type of chemical substance that reacts with a base

An acid is a molecule or ion capable of donating a proton (hydrogen ion H+), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid).

Ultraviolet Electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays

Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.

Photograph image created by light falling on a light-sensitive surface

A photograph is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of what the human eye would see. The process and practice of creating such images is called photography. The word photograph was coined in 1839 by Sir John Herschel and is based on the Greek φῶς (phos), meaning "light," and γραφή (graphê), meaning "drawing, writing," together meaning "drawing with light."

In the graphic arts, photoengraving is used to make printing plates for various printing processes, reproducing a wide variety of graphics such as lettering, line drawings and photographs.

The same procedure is used to make printed circuit boards, foil-stamping dies and embossing dies. It is also used to make nameplates, commemorative plaques and other decorative engravings. It can be used to make flat springs, levers, gears and other practical components that would otherwise be fabricated from sheet metal by cutting, drilling, jigsawing or stamping. A very high degree of precision is possible. In these applications, it is properly called photochemical machining, but the terms photochemical milling, chemical milling and photoetching are sometimes used. A similar process called photolithography is used to make integrated circuits.

Printed circuit board Board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Postage stamp small piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage

A postage stamp is a small piece of paper issued by a post office, postal administration, or other authorized vendors to customers who pay postage, who then affix the stamp to the face or address-side of any item of mail—an envelope or other postal cover —that they wish to send. The item is then processed by the postal system, where a postmark or cancellation mark—in modern usage indicating date and point of origin of mailing—is applied to the stamp and its left and right sides to prevent its reuse. The item is then delivered to its addressee.


A die is a specialized tool used in manufacturing industries to cut or shape material mostly using a press. Like molds, dies are generally customized to the item they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.

Methods

One method of photoengraving produces a shallow depression in the metal. This is used for intaglio printing plates or for decorative purposes. It is also the same method used for printed circuit boards. The engraving is usually made in copper or brass. The process can be done in open trays but is much more effective if the etchant (often ferric chloride) is sprayed onto the metal. When ferric chloride is used as the etchant, no metal parts other than titanium can be used in the etching equipment. Decorative engraving is often filled by spray-painting then sanding to remove the paint from the raised parts of the engraving.

Metal element, compound, or alloy that is a good conductor of both electricity and heat

A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically malleable or ductile. A metal may be a chemical element such as iron; an alloy such as stainless steel; or a molecular compound such as polymeric sulfur nitride.

Intaglio (printmaking) family of printing and printmaking techniques

Intaglio is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink. It is the direct opposite of a relief print.

Copper Chemical element with atomic number 29

Copper is a chemical element with the symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

Another method produces a deep engraving with sloped shoulders. In this method, the metal (usually zinc or magnesium) is held face down and a mixture of nitric acid and a soap-like oil is splashed onto it. As the acid etches the surface, the oil adheres to the edges of the exposed area. This progressively reduces the area being etched, resulting in a sloped edge; a single dot will end up as a cone-shaped mound protruding from the etched area. This method is used for printing plates (the shoulder supports the printing surface), foil stamping dies and embossing dies. Decorative engravings made by this method may go through a second process to produce a decorative background. The raised parts and their shoulders are painted with an etchant-resistant material and a pattern of etchant-resistant material is applied to the deep parts of the engraving. The resist for the background may be another photoengraving or may be randomly splashed on. The engraving is etched again for a short time to produce a raised pattern in the background. Decorative engravings of this type may also be spray-painted and sanded as in the previous method.

Zinc Chemical element with atomic number 30

Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).

Magnesium Chemical element with atomic number 12

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Nitric acid (HNO3), also known as aqua fortis (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid.

In traditional print shop practice, a special very-large-format camera is used to image the source material either directly onto the photosensitive coating, or onto a sheet of photographic film which is then developed and contact-printed onto the coated plate. In large-scale commercial printing, computer-driven optoelectronic equivalents began to replace these methods in the 1970s. In the case of line cuts (graphics in solid blacks and whites without gradations of gray or color), the photoengraving is done on zinc, and the result is called a zinc etching. In the case of halftone cuts, the work is done on copper. The halftone effect is accomplished by photographing the subject through a wire or glass screen, which breaks the image up into a pattern of dots with sizes corresponding to the local brightness of the image; the larger dots create the darker areas, the smaller dots the highlights. The finer the screen, the finer the detail possible in the printed product. Halftones made with a screen having 65 lines to the inch are considered coarse. Those having 150 lines to the inch are considered fine.

Photographic film sheet of plastic coated with light-sensitive chemicals

Photographic film is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film.

Photographic processing or photographic development is the chemical means by which photographic film or paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into a visible image, makes this permanent and renders it insensitive to light.

Contact print photographic image produced from film

A contact print is a photographic image produced from film; sometimes from a film negative, and sometimes from a film positive or paper negative. In a darkroom an exposed and developed piece of photographic film or paper is placed emulsion side down, in contact with a piece of photographic paper, light is briefly shone through the negative or paper and then the paper is developed to reveal the final print.

History

The oldest known print made from a photoengraved plate, by Nicephore Niepce in 1825. It reproduces a 17th-century Flemish engraving. Niepce called the process "Heliography". Nicephore Niepce Oldest Photograph 1825.jpg
The oldest known print made from a photoengraved plate, by Nicéphore Niépce in 1825. It reproduces a 17th-century Flemish engraving. Niépce called the process "Heliography".

The first photoengraving process was developed in the 1820s by Nicéphore Niépce, which used photoresist to make a one-off camera photograph rather than a printing plate. His usual test subjects were paper prints of conventional engravings, and exposure was by contact under direct sunlight rather than by the use of a camera. Several metals were tried for the printing plate, as well as glass and lithographic stone. His first success came in 1822. The earliest known surviving example of a paper print made from one of his photoengraved plates dates to 1825 and reproduces a 17th-century engraving.

Niépce used Bitumen of Judea as the photoresist. Initially soluble in various spirits and oils, a thin coating of bitumen hardens (polymerizes) where it is exposed to light. The unexposed parts can then be rinsed away with a solvent, baring the underlying material, which can then be etched to the desired depth. Niépce's process lay dormant for many years, but it was revived in the 1850s and bitumen was widely used as a photoresist far into the 20th century. Very long exposures in bright light were required, but bitumen had the advantage that it was superbly resistant to strong acids. [1]

The use of photoengraving for a halftone process that could be used to print grayscale photographic images dates all the way back to the 1839 introduction of the daguerreotype, the first practical photographic process. The daguerreotype image consisted of a microscopically fine granular structure on the surface of a silver-plated copper sheet that had been polished to a mirror finish. Methods were soon devised for differentially etching the image grains and the ground so that the daguerreotype could be used as a printing plate. In some instances, very pleasing results were obtained, but exceptional skill and care were required and the very fine structure of the image limited the useful life of each plate to a few hundred prints at best.

Henry Fox Talbot is usually credited with the first workable process for converting a grayscale image into a varying structure of stark black and white that resulted in a reasonably durable printing plate. As with other early halftone processes, the plate could not be combined with ordinary type, so for inclusion in a book or periodical each image had to be printed separately and either bound in or tipped in with an adhesive.

Frederic E. Ives is usually credited with the first commercially successful process that was compatible with ordinary letterpress printing, so that halftone blocks could be printed along with blocks of text in books, periodicals and newspapers. His process came into widespread use during the 1890s, largely replacing the hand-engraved wood and metal blocks that had previously served to provide illustrations.

As in many other fields of invention, there are conflicting claims of priority, instances of simultaneous invention, and variously nuanced definitions of the terminology, so sorting out the merits of the "first" claims made on behalf of the many inventors in the field of halftone reproduction—not infrequently biased by nationalistic sentiments—can be very problematic.

See also

Related Research Articles

Photolithography, also called optical lithography or UV lithography, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a photosensitive chemical photoresist on the substrate. A series of chemical treatments then either etches the exposure pattern into the material or enables deposition of a new material in the desired pattern upon the material underneath the photoresist. In complex integrated circuits, a CMOS wafer may go through the photolithographic cycle as many as 50 times.

Etching intaglio printmaking technique

Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types of material. As a method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today. In a number of modern variants such as microfabrication etching and photochemical milling it is a crucial technique in much modern technology, including circuit boards.

Printmaking activity or occupation of making prints from plates or blocks

Printmaking is the process of creating artworks by printing, normally on paper. Printmaking normally covers only the process of creating prints that have an element of originality, rather than just being a photographic reproduction of a painting. Except in the case of monotyping, the process is capable of producing multiples of the same piece, which is called a print. Each print produced is considered an "original" work of art, and is correctly referred to as an "impression", not a "copy". Often impressions vary considerably, whether intentionally or not. The images on most prints are created for that purpose, perhaps with a preparatory study such as a drawing. A print that copies another work of art, especially a painting, is known as a "reproductive print".

Nicéphore Niépce French inventor and photographer

Joseph Nicéphore Niépce, commonly known or referred to simply as Nicéphore Niépce, was a French inventor, usually credited as the inventor of photography and a pioneer in that field. Niépce developed heliography, a technique he used to create the world's oldest surviving product of a photographic process: a print made from a photoengraved printing plate in 1825. In 1826 or 1827, he used a primitive camera to produce the oldest surviving photograph of a real-world scene. Among Niépce's other inventions was the Pyréolophore, the world's first internal combustion engine, which he conceived, created, and developed with his older brother Claude Niépce.

Aquatint etching technique

Aquatint is an intaglio printmaking technique, a variant of etching that only produces areas of tone rather than lines. For this reason it has mostly been used in conjunction with etching, to give outlines. It has also been used historically to print in colour, both by printing with multiple plates in different colours, and by making monochrome prints that were then hand-coloured with watercolour.

Frederic Eugene Ives American inventor

Frederic Eugene Ives was a U.S. inventor, born at Litchfield, Connecticut. In 1874–78 he had charge of the photographic laboratory at Cornell University. He moved to Philadelphia, Pennsylvania, where in 1885 he was one of the founding members of the Photographic Society of Philadelphia. He was awarded the Franklin Institute's Elliott Cresson Medal in 1893, the Edward Longstreth Medal in 1903, and the John Scott Medal in 1887, 1890, 1904 and 1906. His son Herbert E. Ives was a pioneer of television and telephotography, including color facsimile.

Rotogravure printing process

Rotogravure is a type of intaglio printing process, which involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press. Once a staple of newspaper photo features, the rotogravure process is still used for commercial printing of magazines, postcards, and corrugated (cardboard) and other product packaging.

Photogravure printmaking technique

Photogravure is an intaglio printmaking or photo-mechanical process whereby a copper plate is grained and then coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio plate that can reproduce detailed continuous tones of a photograph.

KPR, originally known as Kodak Photoresist, is a photosensitive material used in photoengraving, Photogravure and photolithography. Once dried KPR can be dissolved by several solvents but after exposure to strong ultraviolet light it hardens and becomes insoluble by some of these solvents. It is also resistant to acid, ferric chloride and other chemicals used to etch metals.

Heliography photographic process invented ca. 1822 by N. Niépce: Judea bitumen coated on glass/metal is exposed to light and washed with lavender oil to keep only light-hardened areas; used to make View from the Window at Le Gras (1826/7)—the oldest extant photo

Heliography from helios, meaning "sun", and graphein (γράφειν), "writing") is the photographic process invented by Joseph Nicéphore Niépce around 1822, which he used to make the earliest known surviving photograph from nature, View from the Window at Le Gras, and the first realisation of photoresist as means to reproduce artworks through inventions of photolithography and photogravure

Zincography printing process with zinc plates

Zincography was a planographic printing process that used zinc plates. Alois Senefelder first mentioned zinc's lithographic use as a substitute for Bavarian limestone in his 1801 English patent specifications. In 1834, Federico Lacelli patented a zincographic printing process, producing large maps called géoramas. In 1837–1842, Eugène-Florent Kaeppelin perfected the process to create a large polychrome geologic map.

Viscosity printing is a multi-color printmaking technique that incorporates principles of relief printing and intaglio printing. It was pioneered by Stanley William Hayter.

Steel engraving

Steel engraving is a technique for printing illustrations based on steel instead of copper. It has been rarely used in artistic printmaking, although it was much used for reproductions in the 19th century. Steel engraving was introduced in 1792 by Jacob Perkins (1766–1849), an American inventor, for banknote printing. When Perkins moved to London in 1818, the technique was adapted in 1820 by Charles Warren and especially by Charles Heath (1785–1848) for Thomas Campbell's Pleasures of Hope, which contained the first published plates engraved on steel. The new technique only partially replaced the other commercial techniques of that time such as woodcut, wood engraving, copper engraving and later lithography. All the illustrations in the Encyclopædia Britannica of 1911 are steel engravings.

Etching (microfabrication) technique in microfabrication

Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete.

Bitumen of Judea, or Syrian asphalt, is a naturally occurring asphalt that has been put to many uses since ancient times. It is a light-sensitive material in what is accepted to be the first complete photographic process, i.e., one capable of producing durable light-fast results. The technique was developed by French scientist and inventor Nicéphore Niépce in the 1820s. In 1826 or 1827, he applied a thin coating of the tar-like material to a pewter plate and took a picture of parts of the buildings and surrounding countryside of his estate, producing what is usually described as the first photograph. It is considered to be the oldest known surviving photograph made in a camera. The plate was exposed in the camera for at least eight hours.

Photochemical machining

Photochemical machining (PCM), also known as photochemical milling or photo etching, is a chemical milling process used to fabricate sheet metal components using a photoresist and etchants to corrosively machine away selected areas. This process emerged in the 1960s as an offshoot of the printed circuit board industry. Photo etching can produce highly complex parts with very fine detail accurately and economically.

Chemical milling or industrial etching is the subtractive manufacturing process of using baths of temperature-regulated etching chemicals to remove material to create an object with the desired shape. It is mostly used on metals, though other materials are increasingly important. It was developed from armor-decorating and printing etching processes developed during the Renaissance as alternatives to engraving on metal. The process essentially involves bathing the cutting areas in a corrosive chemical known as an etchant, which reacts with the material in the area to be cut and causes the solid material to be dissolved; inert substances known as maskants are used to protect specific areas of the material as resists.

Carbon tissue is a gelatin-based emulsion used as a photoresist in the chemical etching (photoengraving) of gravure cylinders for printing. This was introduced by British physicist and chemist Joseph Swan in 1864. It has been used in photographic reproduction since the early days of photography.

References

  1. Niepce House Museum history pages. Retrieved 28 May 2013.

Further reading