Etching is the first indirect technique of engraving used as an expressive means since ancient times, as it gives the artist great creative freedom, without the long apprenticeship that characterises other means of artistic expression.
Its origin most plausibly dates back to the middle ages, when nitric acid (aqua fortis, as the medieval alchemists called it) was used to etch decorations into weapons and armour. Later, in the late fifteenth and early sixteenth century , the technique and name were adopted by engraving artist.
The sequence of engraving is as follows: after cleaning and smoothing the surface, the artist covers it with a thin layer of special wax, which will be darkened with lamp-black to make the wax more resistant to the acid and the engraved lines more visible.

Then the artist uses a stylus to press through the wax and uncover the metal, drawing the lines that will compose the image. Once the edges and the back of the plate are protected, it is immersed in a basin containing some diluted acid.

The most commonly used types of acid are nitric acid and perchloric acid. Nitric acid is almost always used on zinc plates, and perchloric acid on brass and copper. During the "biting", that is the acid's corrosive action, the acid creates small bubbles that settle on the carved drawing. As they form, the artist removes them using the feather of an aquatic bird ( which are the most resistant type), in order to obtain a regular line.
Moreover, during the chemical reaction perchloric acid deposits in the furrows a rust-coloured pulp which impedes the biting; so that plates are often washed or held upside down so that the pulp falls into the basin.
Using a different concentration of acid and varying the biting times different kinds of lines and results can be achieved.

Types of biting:

1) simple - after one immersion in the acid, the lines have all the same strength: the shades and color gradations are created by the more or less dense network of lines.
2) layered - after successive multiple immersions. The engraver immerses the plate in the acid a first time, then covers with a protective wax the lines that must be thinner and lighter in the print. Then the plate is immersed again to obtain thicker lines and the procedure is repeated as many times as required to obtain wider and deeper lines. In the print the sharp edges due to the different moment of biting will be clearly visible.
3) addition - when the darker lines are the first to be engraved and thinner and lighter lines are added step by step through a series of immersions. This method creates not only sharp lines, but also areas of soft shades and nuances, because the artist can change any part of his work until the moment of biting.
Among the first to use this technique are Urs Graf, a goldsmith from Basil and the author of the first dated print (1518), and Dürer, who engraved six iron plates, including The Cannon (1518). However, it was Parmigianino who realised the possibilities of the technique and brought it to perfection.
Original etching spread quickly throughout Europe, taking the place of xylography and partly of the burin, with Rembrandt its major artist. It has to be stressed that original etching is different from reproductive etching, started in the school of Raffaello da Marcantonio Raimondi and created to reproduce the master's works.
Among the major engravers of the seventeenth century are the landscape painters Jacques Callot and Claude Lorrain in France and Stefano della Bella and Giovanni Benedetto Castiglione, called the Grechetto, the inventor of the monotype, in Italy. In the seventeenth century, engravings provided bitter and ironic comments on social miseries and contrasts. (Hogarth, G.B. Tiepolo, Piranesi, Goya, and others). In the eighteenth century lithography, a new technique, was preferred to engraving until Corot, Millet and other impressionists (Pissarro, Manet ...) rediscovered its possibilities. Many modern painters such as Picasso and Braque reached remarkable results with etching, but especially the German impressionists used it, together with lithography, for its graphic expressive strength. As all with the other engraving techniques, etching is today greatly appreciated by both artists and the public.

GIANNI CACCIARINI Ombre e Ombrelli Etching 49.5X33