Suite of Methods IV: Making an Etched Matrix
Etching – a brief background
Current research in the historical print field has very recently pushed back the date for the first extant print produced by etching, with the identification of an intaglio plate by Daniel Hopfer, Die Schlacht von Thérouanne (The Battle of Thérouanne ) as being executed in 1493.
Hopfer was also an artist who had a career designing and decorating armour by etching, before its application to printing, and it appears that it was he who developed the method for use in printing. His first works were etched on iron plates, using beeswax as the ground (acid resistant coating). Presumably, Hopfer began with iron due to his familiarity with the metal through his experience etching on armour.
It is not confirmed as to whether his later works were also on iron, but it is known that subsequent artists began to use copper plates, as iron was prone to rust and corrosion. Better grounds were also developed, as beeswax was prone to foul biting (breakdown of the ground, allowing acid to bite areas which should not be bitten).
It was not long before many artists saw the potential for etching to rival engraving, as this new method was easier and more accessible, not needing years of training to produce the matrix. It was also possible to draw directly and spontaneously onto the plate, in almost the same way as drypoint, but with almost the same durability as engraving.
Etching – producing an etched matrix for Intaglio printing
Image based on:
In producing a matrix by etching, a metal plate is used. After the initial period of using iron, copper plates were quickly adopted, as they were already available for use in engraving, and were not prone to rust and corrosion, as iron was.
The plate is prepared for etching by covering the surface with a thin coating of ground, or resist, so-called because it resists the acid which is used to bite the lines of the image. Before this is done, however, the plate must be free of any dirt or oils which would prevent the ground from coating evenly.
This initial process is called degreasing the plate. A number of liquids are suitable for use, the most popular being ammonia or white vinegar. Usually, whiting (washed and ground white chalk) is added to make a paste, and the paste rubbed onto the surface of the plate. After rinsing, water should run off the plate evenly, with no areas of repulsion or beading.
The plate must be completely dry before moving onto the next step, which is applying the ground. In pre-1600 Europe, each artist would have made their own ground, according to their need or preference. A ground may be liquid, and applied with a brush or sponge, or hard. Hard ground is made in a block or ball, and applied to a plate which has been heated. The hard ground melts and is spread over the surface, then allowed to cool and harden. Both soft and hard grounds are made with a combination of beeswax and/or oil varnish and/or rosin, in varying ratios.
At some point before the plate is immersed in acid, the back/reverse must be made acid-proof as well. In modern practice, commercially-available zinc plate already has a plastic backing. For this experiment, I have used shellac, as it was easily accessible and resistant.
Once the plate is coated on both sides, the image can be produced. Following the pattern used for other methods in this suite, I traced the basic lines from the image I had chosen.
Then the traced image could be fleshed out to the level of detail I felt could be achieved, according to the method. This was reversed and rubbed onto the plate using a bone folder.
The image is then developed on the matrix by using a scribe, or etching needle, to draw through the ground. This reveals the metal underneath, exposing it so the metal will make contact with the acid when it is immersed. The scribe is held like a pencil and used in the same way. It is also possible to skip the step of transferring an image, and draw with the scribe directly onto the prepared plate.
The acid used in both the historical and modern period is Nitric Acid, or Aqua Fortis. The solution varies, usually 1:4 or 1:8, or even weaker. The matrix is carefully lowered into the acid, and left for increments of time according to the effect desired. The longer then plate is left in, the deeper the lines will etch, however, this will also eventually break the ground down, starting with the areas around the linework.
According to the strength and freshness of the acid solution and the width of the lines scribed, bubbles will begin to form on the exposed metal. This is a good indication of how fresh or strong the acid is – both will affect how the plate is bitten, or etched. The bubbles are periodically removed by feathering – lowering a feather into the acid and stroking the surface of the plate. The feather is gentle but effective, and does not damage the ground. It is, of course, slowly eaten away over time by the acid.
Removing the bubbles periodically ensures that the lines bite evenly. If the bubbles are left on the plate, the exposed metal underneath/inside the bubble is not bitten at the same rate as other exposed areas. There can even be an uneven texture left behind which indicates areas where the acid bit around, but not inside, the bubble.
This plate was etched for somewhere between 15 and 20 minutes, in 5 minute increments. Each time, the plate is removed using an inert object such as a wooden or plastic spatula, rinsed, and observed. A fingernail or the tip of a scribe can be placed carefully into the incised lines to check the depth of the bite.
Once the desired depth of bite or etch has been achieved, the plate can be cleaned off using oil or turpentine, and it is ready for printing by the intaglio method.