Etching is the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio in the metal (the original process—in modern manufacturing other chemicals may be used on other types of material). As an intaglio method of printmaking it is, along with engraving, the most important technique for old master prints, and remains widely used today.
In pure etching, a metal (usually copper, zinc or steel) plate is covered with a waxy ground that is resistant to acid (and alkali). The artist then scratches off the ground with a pointed etching needle where he/she wants a line to appear in the finished piece, so exposing the bare metal. The échoppe, a tool with a slanted oval section is also used for "swelling" lines. The plate is then dipped in a bath of acid, technically called the mordant (French for "biting"), or has acid washed over it. The acid "bites" into the metal, where it is exposed, leaving behind lines sunk into the plate. The remaining ground is then cleaned off the plate. The plate is inked all over, and then the ink wiped off the surface, leaving only the ink in the etched lines.
The plate is then put through a high-pressure printing press together with a sheet of paper (often moistened to soften it). The paper picks up the ink from the etched lines, making a print. The process can be repeated many times; typically several-hundred impressions (copies) could be printed before the plate shows much sign of wear. The work on the plate can also be added to by repeating the whole process; this creates an etching which exists in more than one state.
Etching by goldsmiths and other metal-workers in order to decorate metal items such as guns, armour, cups and plates has been known in Europe since the Middle Ages at least, and may go back to antiquity. The elaborate decoration of armour, in Germany anyway, was an art probably imported from Italy around the end of the fifteenth century—little earlier than the birth of etching as a printmaking technique. The process as applied to printmaking is believed to have been invented by Daniel Hopfer (circa 1470-1536) of Augsburg, Germany. Hopfer was a craftsman who decorated armour in this way, and applied the method to printmaking, using iron plates (many of which still exist). Apart from his prints, there are two proven examples of his work on armour: a shield from 1536 now in the Real Armeria of Madrid and a sword in the Germanisches Nationalmuseum of Nuremberg. An Augsburg horse armour in the German Historical Museum, Berlin, dating to between 1512 and 1515, is decorated with motifs from Hopfer's etchings and woodcuts, but this is no evidence that Hopfer himself worked on it, as his decorative prints were largely produced as patterns for other craftsmen in various media. The switch to copper plates was probably made in Italy, and thereafter etching soon came to challenge engraving as the most popular medium for artists in printmaking. Its great advantage was that, unlike engraving which requires special skill in metalworking, etching is relatively easy to learn for an artist trained in drawing.
Jacques Callot (1592-1635) from Nancy in Lorraine (now part of France) made important technical advances in etching technique. He developed the échoppe, a type of etching-needle with a slanting oval section at the end, which enabled etchers to create a swelling line, as engravers were able to do.
He also seems to have been responsible for an improved, harder, recipe for the etching ground, using lute-makers' varnish rather than a wax-based formula. This enabled lines to be more deeply bitten, prolonging the life of the plate in printing, and also greatly reducing the risk of "foul-biting," where acid gets through the ground to the plate where it is not intended to, producing spots or blotches on the image. Previously the risk of foul-biting had always been at the back of an etcher's mind, preventing him from investing too much time on a single plate that risked being ruined in the biting process. Now etchers could do the highly detailed work that was previously the monopoly of engravers, and Callot made full use of the new possibilities.
He also made more extensive and sophisticated use of multiple "stoppings-out" than previous etchers had done. This is the technique of letting the acid bite lightly over the whole plate, then stopping-out those parts of the work which the artist wishes to keep light in tone by covering them with ground before bathing the plate in acid again. He achieved unprecedented subtlety in effects of distance and light and shade by careful control of this process. Most of his prints were relatively small—up to about six inches or 15 cm on their longest dimension, but packed with detail.
One of his followers, the Parisian Abraham Bosse, spread Callot's innovations all over Europe with the first published manual of etching, which was translated into Italian, Dutch, German and English.
The seventeenth century was the great age of etching, with Rembrandt, Giovanni Benedetto Castiglione and many other masters. In the eighteenth century, Piranesi, Tiepolo and Daniel Chodowiecki were the best of a smaller number of fine etchers. In the nineteenth and early-twentieth centuries, the etching revival produced a host of lesser artists, but no really major figures. Etching is still widely practiced today.
A waxy acid-resist, known as a ground, is applied to a metal plate, most often copper or zinc but steel plate is another medium with different qualities. There are two common types of ground: hard ground and soft ground.
Hard ground can be applied in two ways. Solid hard ground comes in a hard waxy block. To apply hard ground of this variety, the plate to be etched is placed upon a hot-plate (set at 70 degrees C), a kind of metal worktop that is heated up. The plate heats up and the ground is applied by hand, melting onto the plate as it is applied. The ground is spread over the plate as evenly as possible using a roller. Once applied the etching plate is removed from the hot-plate and allowed to cool which hardens the ground.
After the ground has hardened the artist "smokes" the plate, classically with three beeswax tapers, applying the flame to the plate to darken the ground and make it easier to see what parts of the plate are exposed. Smoking not only darkens the plate but adds a small amount of wax. Afterwards the artist uses a sharp tool to scratch into the ground, exposing the metal.
The second way to apply hard ground is by liquid hard ground. This comes in a can and is applied with a brush upon the plate to be etched. Exposed to air the hard ground will harden. Some printmakers use bitumen as hard ground, although often bitumen is used to protect steel plates from rust and copper plates from aging.
Soft ground also comes in liquid form and is allowed to dry but it does not dry hard like hard ground and is impressionable. After the soft ground has dried, the printmaker may apply materials such as leaves, objects, hand prints and so on, which will penetrate the soft ground and expose the plate underneath.
The ground can also be applied in a fine mist, using powdered rosin or spraypaint. This process is called aquatint, and allows for the creation of tones, shadows, and solid areas of color.
The design is then drawn (in reverse) with an etching-needle or échoppe. An "echoppe" point can be made from an ordinary tempered steel etching needle, by grinding the point back on a carborundum stone, at a 45–60 degree angle. The "echoppe" works on the same principle that makes a fountain pen's line more attractive than a biro's: The slight swelling variation caused by the natural movement of the hand "warms up" the line, and although hardly noticeable in any individual line, has a very attractive overall effect on the finished plate. It can be drawn with in the same way as an ordinary needle
The plate is then completely submerged in an acid that eats away at the exposed metal. Ferric chloride may be used for etching copper or zinc plates, whereas nitric acid may be used for etching zinc or steel plates. Typical solutions are two parts FeCl3 to two parts water and one part nitric to three parts water. The strength of the acid determines the speed of the etching process.
During the etching process the printmaker uses a bird feather or similar item to wave away bubbles and detritus produced by the dissolving process, from the surface of the plate, or the plate may be periodically lifted from the acid bath. If a bubble is allowed to remain on the plate then it will stop the acid biting into the plate where the bubble touches it. Zinc produces more bubbles much more rapidly than copper and steel and some artists use this to produce interesting round bubble-like circles within their prints for a Milky Way effect.
The detritus is powdery dissolved metal that fills the etched grooves and can also block the acid from biting evenly into the exposed plate surfaces. Another way to remove detritus from a plate is to place the plate to be etched face down within the acid upon plasticine balls or marbles, although the drawback of this technique is the exposure to bubbles and the inability to remove them readily.
For aquatinting a printmaker will often use a test strip of metal about a centimeter to three centimeters wide. The strip will be dipped into the acid for a specific number of minutes or seconds. The metal strip will then be removed and the acid washed off with water. Part of the strip will be covered in ground and then the strip is redipped into the acid and the process repeated. The ground will then be removed from the strip and the strip inked up and printed. This will show the printmaker the different degrees or depths of the etch, and therefore the strength of the ink color, based upon how long the plate is left in the acid.
The plate is removed from the acid and washed over with water to remove the acid. The ground is removed with a solvent such as turpentine. Turpentine is often removed from the plate using methylated spirits since turpentine is greasy and can affect the application of ink and the printing of the plate.
Spit-biting is a process whereby the printmaker will apply acid to a plate with a brush in certain areas of the plate. The plate may be aquatinted for this purpose or exposed directly to the acid. The process is known as "spit"-biting due to the use of saliva once used as a medium to dilute the acid, although gum arabic or water are now commonly used.
A piece of matte board, a plastic "card," or a wad of cloth is often used to push the ink into the incised lines. The surface is wiped clean with a piece of stiff fabric known as tarlatan and then either wiped with newsprint paper; some printmakers prefer to use the blade part of their hand or palm at the base of their thumb. The wiping leaves ink in the incisions. You may also use a folded piece of organza silk to do the final wipe. If copper or zinc plates are used plate surface is left very clean and therefore white in the print. If steel plate is used then the plate's natural tooth gives the print a gray background similar to the effects of aquatinting. As a result steel plates do not need aquatinting as gradual exposure of the plate via successive dips into acid will produce the same result.
A damp piece of paper is placed over the plate and it is run through the press.
Growing concerns about the health effects of acids and solvents led to the development of less toxic etching methods in the late twentieth century. An early innovation was the use of floor wax as a hard ground for coating the plate. Others, such as printmakers Mark Zaffron and Keith Howard, developed systems using acrylic polymers as a ground and ferric chloride for etching. The polymers are removed with sodium carbonate (washing soda) solution, rather than solvents. When used for etching, ferric chloride does not produce a corrosive gas, as acids do, thus eliminating another danger of traditional etching.
The traditional aquatint, which uses either powdered rosin or enamel spray paint, is replaced with an airbrush application of the acrylic polymer hard ground. Again, no solvents are needed beyond the soda ash solution, though a ventilation hood is needed due to acrylic particulates from the airbrush spray.
The traditional soft ground, requiring solvents for removal from the plate, is replaced with water-based relief printing ink. The ink receives impressions like traditional soft ground, resists the ferric chloride etchant, yet can be cleaned up with warm water and either soda ash solution or ammonia. Etching is a form of art which is taught in many ways.
Light sensitive polymer plates allow for photorealistic etchings. A photo-sensitive coating is applied to the plate by either the plate supplier or the artist. Light is projected onto the plate as a negative image to expose it. Photopolymer plates are either washed in hot water or under other chemicals according to the plate manufacturers' instructions. Areas of the photo-etch image may be stopped-out before etching to exclude them from the final image on the plate, or removed or lightened by scraping and burnishing once the plate has been etched. Once the photo-etching process is complete, the plate can be worked further as a normal intaglio plate, using drypoint, further etching, engraving, and so forth. The final result is an intaglio plate which is printed like any other.
Copper was always the traditional metal, and is still preferred, for etching, as it bites evenly, holds texture well, and does not distort the color of the ink when wiped. Zinc is cheaper than copper, so preferable for beginners, but it does not bite as cleanly as copper, and it alters some colors of ink. Steel is growing in popularity as an etching substrate. Prices of copper and zinc have steered steel to an acceptable alternative. Line quality of steel is less fine than copper but finer than zinc. Steel has a natural and rich aquatint. Steel is virtually impossible to reclaim though the price and availability make it still more cost effective.
There are many ways for the printmaker to control the acid's effects. Most typically, the surface of the plate is covered in a hard, waxy 'ground' that resists acid. The printmaker then scratches through the ground with a sharp point, exposing lines of metal that are attacked by the acid.
Aquatint is a variation in which particulate resin is evenly distributed on the plate, then heated to form a screen ground of uniform but less than perfect density. After etching any exposed surface will result in a roughened (i.e. darkened) surface. Areas that are to be light in the final print are protected by varnishing between acid baths. Successive turns of varnishing and placing the plate in acid create areas of tone difficult or impossible to achieve by drawing though a wax ground.
Printing the plate is done by covering the surface with ink, then rubbing the ink off the surface with tarlatan cloth or newsprint, leaving ink in the roughened areas and lines. Damp paper is placed on the plate, and both are run through a printing press; the pressure forces the paper into contact with the ink, transferring the image. Unfortunately, the pressure also subtly degrades the image in the plate, smoothing the roughened areas and closing the lines; a copper plate is good for, at most, a few hundred printings of a strongly etched imaged before the degradation is considered too great by the artist. At that point, the artist can manually restore the plate by re-etching it, essentially putting ground back on and retracing their lines; alternately, plates can be electroplated before printing with a harder metal to preserve the surface. Zinc is also used, because as a softer metal, etching times are shorter; however, that softness also leads to faster degradation of the image in the press.
Faux-bite or "over-biting" is common in etching, and is the effect of minuscule amounts of acid leaking through the ground to create minor pitting and burning on the surface. This incidental roughening may be removed by smoothing and polishing the surface, but artists often leave faux-bite or deliberately court it by handling the plate roughly, because it is viewed as a desirable mark of the process.
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