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Most etching falls into two categories: artistic or industrial. Artistic examples are a way of creating two-dimensional paintings or drawings from something that has three dimensions, usually by rubbing or pressing a paper against the surface to be etched. People can use this technique to make prints of things that already exist, like coins or metal plates, though many choose to actually make these objects themselves first. There are several different ways of going about the practice, but most artists use a hard-ground, soft-ground, or aquatint approach. Color printing projects can be done as reliefs, too, with different layers exposing different colors and striations. Industrial etches, on the other hand, are usually used to do things like affix serial numbers onto computer chips, imprint memory boards for electronics, or to cut glass or plasma. The techniques in these settings tend to be totally different, and are often done by machine rather than by hand. In both the arts and industry, the practice has a history of using corrosive chemicals. A lot of this has changed in modern times, but some people still raise health concerns about the practice. In general, so long as the space is ventilated and the technicians take proper precautions, there isn’t usually much cause for concern.
In hard-ground scenarios, an acid-resistant coating, called a ground, is applied to a metal plate made of copper, zinc, or steel. The artist creates marks on the ground with a needle, which causes exposure of the metal. In most cases the artist will use an échoppe or a special swelling needle to create the “swelling lines,” which are the notations for where the final picure or image will be most prominent. The plate is then dipped into acid to create a “biting” effect on the exposed metal, which leaves actual lines on the plate in the places marked.
Remnants of the ground are then wiped off, and the artist applies ink or other pigment to the plate. The ink sinks into the lines and the rest of it is cleaned. A sheet of paper covering the metal plate is passed through a high-pressure printing press where the ink is transferred to the paper and a print is made. Depending on the type of metal and acid used, different characters, scenes, and depictions can be created.
As its name implies, soft-ground projects use a softer coating that typically contains about one-third grease, which is the main difference between hard-ground and soft-ground methods. To produce an image, a sheet of paper is placed on a metal plate that has been coated with the soft ground. The artist draws an image using a pencil on the paper, causing the ground to stick to the paper and leaving the metal exposed.
Artists who are going for a more distinctive look may choose to use aquatint, a method that involves colored pigments on a copper or zinc plate. The alloys in these metals have a different way of binding to ink pigmentation. In most cases the artist is able to create a tonal effect using either a powdered resin or enamel spray paint in the ground. The rest of the process is similar to that of the hard-ground process. Francisco de Goya, the famous Spanish painter and printmaker, used aquatint almost exclusively in his works.
Relief making requires that the background areas are exposed to acid, which makes it different from grounded and aquatint preparations where the design itself is what gets the caustic exposure. This method was used by 18th-century English poet William Blake to illustrate many of his works and published collections, as well as in the creation of several stand-alone pieces. The technique is popularly used for color printing, with different levels inked for different colors.
Etches are also very common in many facets of modern manufacturing, though in nearly all instances the intent here is far from aesthetic. The technique can ensure uniformity and precision, which is really important for electronics and other mechanical instruments. Some of the most common mediums in the industrial sector include chemical resins, plasma, printed circuit board, and glass. The technique is also popular in industries such as semiconductor fabrication, and many militaries depend on this sort of technology for the large-scale manufacturing of firearms and other highly specialized instruments.
The use of toxic substances in both artistic and industrial processes has raised some health concerns, although in most cases there isn’t much risk so long as the exposure is brief and the chemicals are used sparingly. Some changes in the way things are done have also worked to mitigate some of the more serious risks. In the case of hard and soft-ground etches, acrylic polymers have largely replaced more toxic substances that were once used. These sorts of polymers are often applied by airbrush for aquatint projects, and water-based relief printing inks have largely replaced some of the harsher substances used in relief making. Solvents to remove ground or ink have been largely replaced with sodium carbonate, and ferric chloride is often used instead of harsh acids in industrial settings.