Etching is the method of engraving using acid on a metal surface. It is also a printmaking method wherein the image is carved into a surface of a metal plate with the use of an acid. This acid bores into the metal surface, and leaves behind rough areas or lines if the surface is too narrow.

Etching is a process which is believed to have started in Augsburg, Germany, by Daniel Hopfer who used the technology in armor making. Later on, the method was applied to printmaking.

The metal plate used in etching is usually copper or zinc, which has a thin coating of resin that is resistant to acid. This coating can also be made of some waxy material. The metal plates are usually smoked so that the engravings and lines become clearly visible through the resin. A sharp tool then scratches the metal and exposes it without actually penetrating it.

As the etching design is completed, the plate is immersed in an acidic solution that attacks the exposed metal parts. During this process, called a bath, the plate is immersed, but frequently removed until the lines are etched to their satisfactory depth.

A coating varnish is then applied to stop the acid from attacking the metal surface further. In this process, the lines which were exposed to the acids longer get the darker prints. Other etchers also apply the acids directly on the plate’s surface.

In printmaking; however, the varnish is removed, and the plate is coated with ink after being warmed or heated. The ink is then wiped carefully so that enough amounts remain the etched depressions. A soft, moist paper is then used to cover the plate, and ran through an etching press.

There is a wide range of modifications in etching techniques. Some etchers modify their products by removing undesired lines. They do this by burnishing or by modifying the original state of the plate after their trial print.

Prints appear differently in various stages, and only a few first prints can be made out of a single plate. Etchers also destroy these plates after making a number of prints.

Several methods of etching produce different effects. Soft-ground etching looks like a pencil drawing, while aquatint produces an effect similar to wash drawing. Aquatint is usually used in combination with hard-ground etching.

Pictorial etching, which evolved from burin engraving also originated from Germany, where artists etched on iron as the earliest example of this delicate form of art.

Nowadays, the popular methods of etching are wet and dry etching. Wet etching is a simple method that requires a container or bin with a solution that is meant to dissolve the metal used.

The downside of this process is that it needs a mask to selectively etch the plate, and one has to find a mask that will not dissolve in the prepared solution. This process is fairly suitable for etching on thin films.

Dry etching, is divided into three classes, namely, reactive ion etching (RIE), sputter etching, and vapor phase etching. Several gases are introduced in the RIE method, where plasma is mixed in the gas to break gas molecules into ions. The ions are then accelerated and start reacting to the metal surface.

Sputter etching is similar to RIE, but without the reactive ions. Vapor phase method is the simplest dry etching technique. In this method, the metal plate is placed inside a chamber, where gases are introduced. The design is then dissolved at the metal surface by the chemical reaction with the gas molecules.

The most popular vapor phase etching techniques are silicon dioxide etching (uses hydrogen fluoride) and silicon etching (uses xenon diflouride).