Photoengraving
Encyclopedia
Photoengraving also known as photo-chemical milling
is a process of engraving
using photographic processing
techniques. The full form of photoengraving is photo mechanical process in the graphic arts, used principally for reproducing illustrations. The subject is photographed, and the image is recorded on a sensitized metal plate, which is then etched in an acid
bath. In the case of line cuts (drawings in solid blacks and whites without gradations of 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 light rays
so that the metal plate is sensitized in a dotted pattern; the larger dots create the darker areas, the smaller dots the high lights. The finer the screen, the greater the precision of detail 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.
The most common type of photoengraving involves using a material that is photosensitive and resistant to acid
s or other etching compounds. This material, called a photoresist
, is applied to a metal to be engraved. It is then exposed to light (usually strong ultraviolet
) through a photographic
negative causing it to harden where the negative allows light to pass. The photoresist is then developed by washing in a solvent
that removes the unhardened parts. Finally, the metal to be engraved is exposed to an acid or other etching compound which dissolves the exposed parts of the metal.
Photoengraving is used to make printed circuit board
s, printing plates, foil-stamping
dies
and embossing dies. It is also used to make nameplate
s, commemorative plaque
s and other decorative engravings. A similar process called photolithography
is used to make integrated circuits.
. 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.
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
dyes and embossing dyes. 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-resistive material and a pattern of etchant-resistive 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.
patented some of his pioneering work for a prototype
of photoengraving. During the 1880s photoengraving techniques had developed further and by the end of the century the process had dramatically improved the look of newspapers and enhanced advertisements with better graphics.
John C. Moss
(January 5, 1838—April 8, 1892) invented the first practicable photo-engraving process in 1863. It led to a revolution in printing and eventually to the mass marketing of newspapers and magazines and books which combined photographs with traditional text.
Milling
Milling may refer to:* Milling , the process of grinding grain or other materials in a mill* Milling machine, a cutting and shaping equipment* Photochemical milling * a part of the leather crusting process...
is a process of engraving
Engraving
Engraving is the practice of incising a design on to a hard, usually flat surface, by cutting grooves into it. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an intaglio printing plate, of copper or another metal, for printing...
using photographic processing
Photographic processing
Photographic processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image...
techniques. The full form of photoengraving is photo mechanical process in the graphic arts, used principally for reproducing illustrations. The subject is photographed, and the image is recorded on a sensitized metal plate, which is then etched in an acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
bath. In the case of line cuts (drawings in solid blacks and whites without gradations of 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
Halftone
Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing...
effect is accomplished by photographing the subject through a wire or glass screen, which breaks the light rays
Ray (optics)
In optics, a ray is an idealized narrow beam of light. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. This allows even very...
so that the metal plate is sensitized in a dotted pattern; the larger dots create the darker areas, the smaller dots the high lights. The finer the screen, the greater the precision of detail 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.
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s or other etching compounds. This material, called a photoresist
Photoresist
A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....
, is applied to a metal to be engraved. It is then exposed to light (usually strong ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
) through a photographic
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
negative causing it to harden where the negative allows light to pass. The photoresist is then developed by washing in a solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
that removes the unhardened parts. Finally, the metal to be engraved is exposed to an acid or other etching compound which dissolves the exposed parts of the metal.
Photoengraving is used to make printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s, printing plates, foil-stamping
Postage stamp
A postage stamp is a small piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage. Typically, stamps are made from special paper, with a national designation and denomination on the face, and a gum adhesive on the reverse side...
dies
Die (manufacturing)
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create...
and embossing dies. It is also used to make nameplate
Nameplate
A nameplate identifies and displays a person or product's name. Name plates are usually shaped as rectangles but are also seen in other shapes, sometimes taking on the shape of someone’s name...
s, commemorative plaque
Commemorative plaque
A commemorative plaque, or simply plaque, is a plate of metal, ceramic, stone, wood, or other material, typically attached to a wall, stone, or other vertical surface, and bearing text in memory of an important figure or event...
s and other decorative engravings. A similar process called photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
is used to make integrated circuits.
Methods
One method of photoengraving produces a shallow depression in the metalMetal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
. This is used for intaglio
Intaglio (printmaking)
Intaglio is a family of printmaking techniques in which the image is incised into a surface, known as the matrix or plate, and the incised line or area holds the ink. Normally, copper or zinc plates are used as a surface, and the incisions are created by etching, engraving, drypoint, aquatint or...
printing plates or for decorative purposes. It is also the same method used for printed circuit boards. The engraving is usually made in copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
or brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
. The process can be done in open trays but is much more effective if the etchant (often ferric chloride
Iron(III) chloride
Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...
) is sprayed onto the metal. When ferric chloride is used as the etchant, no metal parts other than titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
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.
Another method produces a deep engraving with sloped shoulders. In this method the metal (usually zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
or magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
) is held face-down and a mixture of nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and a soap-like
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
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
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped mound protruding from the etched area. This method is used for printing plates (the shoulder supports the printing surface), foil stamping
Foil stamping
Foil stamping, typically a commercial print process, is the application of pigment or metallic foil, often gold or silver, but can also be various patterns or what is known as pastel foil which is a flat opaque color or white special film-backed material, to paper where a heated die is stamped onto...
dyes and embossing dyes. 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-resistive material and a pattern of etchant-resistive 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.
History
In 1852, William Fox TalbotWilliam Fox Talbot
William Henry Fox Talbot was a British inventor and a pioneer of photography. He was the inventor of calotype process, the precursor to most photographic processes of the 19th and 20th centuries. He was also a noted photographer who made major contributions to the development of photography as an...
patented some of his pioneering work for a prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
of photoengraving. During the 1880s photoengraving techniques had developed further and by the end of the century the process had dramatically improved the look of newspapers and enhanced advertisements with better graphics.
John C. Moss
John C. Moss
John Calvin Moss was an American inventor credited with developing the first practicable photo-engraving process in 1863...
(January 5, 1838—April 8, 1892) invented the first practicable photo-engraving process in 1863. It led to a revolution in printing and eventually to the mass marketing of newspapers and magazines and books which combined photographs with traditional text.