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Apart from engraving techniques of direct incision a large range based on chemical incision exists, in which the metal plate is bitten by means of a mordent.

Etching is the most important technique in this group and at the roots of all others. The artist carves into the desired areas using a nitric acid solution, commonly known as aqua-fortis. Nowadays etching is a general term not only for engravings carried out with nitric acid, but indistinctly applied to any etching done with, for instance, iron perchloride or hydrochloric acid.

The metal plate must be protected from overall mordent action, and is therefore covered with an acid-resist or ground which is sufficiently ductile to allow drawing and to expose the metal under the artist’s traces, while being resistant to the mordent. This protective ground normally contains a resin or wax base which makes it tougher and more resistant, while Jew’s pitch is added to achieve a dark tone that helps to distinguish the artist’s traces and adds further protection against the mordent. After the printing plate has been cleaned of greasy or oily impurities and the ground applied, the image may be traced upon it with a stylus, exposing the metal accordingly. After the image has been engraved, the plate is bathed in a mordent solution to bite the drawing. Bathing time depends on various factors: the desired trace depth, the mordent degree or acid/salt concentration used, the working temperature, whether the acids have been employed previously etc.. The degree of concentration is measured on the Beaumé scale with a muriatic acid densimetre. With a copper plate the most adequate acid to be used is Dutch mordant, a solution of hydrochloric acid, potassium chlorate and water. This mordent is slow but remains closest to the etcher’s traces and gives excellent results for aquatint and fine textures. Nitric acid is as often used as Dutch mordant but whereas its reaction time is much faster, the results are less accurate. It is mostly applied on zinc plates, which in turn are used frequently. Another oft-employed mordent on copper plates is iron perchloride, a nontoxic salt which does not cause fumes or burns but does leave aggressive stains. Although it is as slow as Dutch acid, it creates clear and delicate traces.
 









 

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 Printmaking:  Engraving  ·  The original print  ·  Etching  ·  Printing  

 

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