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According to the English definition, etching refers to the process of producing a printing pattern using engraved surfaces of metal. Basically, it involves the usage of strong acid or mordant to cut into the metal surface and creating an artwork in intaglio. Different types include hard-ground, soft-ground, aquatint, relief etching, and non-toxic.
In modern manufacturing, various types of etching are used, including chemical, plasma, printed circuit board, and glass. They are applied in industries such as semiconductor and micro-fabrication. Nevertheless, the traditional methods remain the most common and widely used. There is ample evidence of traditional etching in various historical artifacts such as armors, cups, and plates, and there are a number of different methods that can be used to engrave items.
In hard-ground etching, 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, causing exposure of the metal. For swelling lines, an échoppe or special swelling needle is used. The plate is then dipped into acid to create a “biting” effect on the exposed metal, which leaves lines on the plate.
Remnants of the ground are wiped off, and ink is applied 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, the ink is transferred to the paper, and a print is made. Depending on the type of metal and acid used, different characters can be created.
As its name implies, soft-ground etching uses a special soft ground that contains 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.
In aquatint etching, only copper or zinc plate is used. A tonal effect is created using powdered resin or enamel spray paint in the ground. The rest of the process is similar to that of the hard-ground process. Goya, the famous Spanish painter and printmaker, used aquatint in his works.
Unlike hard-ground etching, in which the design is exposed to acid and inked to produce a print, in relief etching, the background areas are exposed to acid. This method was used by William Blake, the English poet. More recently, it is used for color printing, with different levels inked for different colors.
The use of toxic substances to produce the engraving has raised some health concerns, although changes in the technology have been made. In the case of hard-ground etching, acrylic polymers have replaced more toxic substances that were once used. For aquatint, acrylic polymers are applied by airbrush. Water-based relief printing inks have replaced some soft ground substances. Solvents to remove ground or ink have been replaced with sodium carbonate, while ferric chloride has replaced harsh acids.