Etching is a set of techniques to make images on metal using a corrosive liquid. In the past, the liquid contained acid, usually nitric, but today, it is possible to etch copper with a salt, Iron Chloride, in a water solution. It is also possible to etch zinc and steel, but we prefer copper, because it is the only correct metal that can be etched without acid.
To etch copper, the plate is covered with a soft varnish, also called a ground, then we draw with a point. The plate is put in a bath of corrosive liquid. Where the point has removed the ground, the naked metal will be dissolved by the liquid, leaving a groove. It is these grooves, filled with ink, transferred on the paper by the press, that will make an inverted picture of the drawing etched in the copper.
The kind of the varnish that protects the metal from corrosion defines the different techniques of etching. The best known is also called etching, I have just given an idea of it, it is the oldest. The varnish used in this technique is the hard ground. Aquatint and soft ground are other techniques of etching presented in next pages.