Etching is a process that uses a metal plate to produce an imprint of an image in dampened paper when inked and passed through a roller press. Here is a photo of 3 of my own acid bath etching plates and the inks used:
As you can see, the etching plate is made to carry a charge of printing ink by having lines and textures “etched” on its surface. This may be done in a number of ways – drypoint and acid bath being two of the most frequently used. All design work and the creation of the plates has to be carried out in reverse.
With Drypoint, the plate is scored “dry” with a variety of hard metal points. Drypoint has a lovely, immediate and rather rugged printing effect, because the “burr” thrown up by scoring the plate plays a part in the way the ink is held and deposited on the paper. Another of the direct methods is Mezzotint, in which the whole plate is burred using a rocker to produce a surface that will print a dark, shadowy ground, and then the subject-matter of the image is raised out of the ground by killing the burrs where you want highlights – ie the plate holds no ink or less ink in those spots and the white paper shows through. I must admit mezzotint has always appealed to me though I have never tried it.
With acid bath etching, the pits and score lines in the metal that hold the ink are made by etching them out in an acid solution.. There are no burrs, because the metal is simply eaten away.
Briefly, the plate is first covered with a layer of acid-resistant compound called “tusche”. Lines and textures are inscribed in the tusche using a metal point and the whole plate is dropped into an acid bath, where the acid eats away the metal left bare by scoring through the tusche. This produces the marks that will hold the ink.
Usually the first step with an acid bath etching is to get the linear aspects of the design etched out, and some prints may be made at that stage, before texture is added.
There are various ways of debriding the tusche to produce texture on the plate, so the acid etching process usually requires more than one immersion of varying duration, depending on the depth of line you want and how much ink you want it to hold. There is some skill in assessing the depth of line required for the effects you are looking for.
The inking of the plate is an art in itself. Ink is applied using a special open-weave and slightly abrasive cotton material, and wiped off, leaving ink sitting only in the incisions of the plate. Varying effects can also be produced at this stage by the way the plate is inked. The “Flight” image by Rona Swallow in my main page about Print Making shows great skill in applying 3 colors to one plate.
Here are the 3 etchings printed from the 3 plates in the photo above. Click on images for larger size and more details: