Close up of zinc and copper plates.
Plates and Acids
- Zinc plates are often used for etching. They are etched with a relatively weak nitric acid/water solution often in the range between 6:1 to 15:1. The faster the plate etches, the rougher-ragged the etched marks will be. Zinc plates have the advantage of being softer than copper or steel. This makes them easier to use if you are scraping and burnishing the plate. However, for finer lines, engraving, or stablity over long print runs, the softness is a disadvantage. Nitric acid will etch a zinc plate outwards once it gets below the surface. This makes it easier to "foul-bite" or "false-bite" a plate; this is also called "crevˇ". (see figure 3)
- Copper, another common etching plate material, is much harder than zinc. It is etched using a Ferric Chloride solution, Dutch Mordant (water, hydrochloric acid and potassium chlorate), or a very powerful nitric acid (1:2). Ferric chloride and dutch mordant etch very sharp lines and fine aquatints. Ferric chloride is often etched upside down to allow sediment to fall out of the areas that are etching. Copper etches "cleanly" because the acids tend to bite straight down into the plate rather than spreading outwards like in zinc etching. Because of its hardness, it is more suitable for drypoint and engraving. As with zinc, the hardness may be to your advantage or disadvantage. For added stability, copper is also sometimes steelfaced. This involves coating the entire plate with a microscopicly thin layer of steel.
- Bronze plates are yet another option. I used this type of plate material at the "Taller del Alquimista" in Valparaiso, Chile. We used bronze because even though Chile is one of the worlds major copper producers, it is hard to get a high grade copper that would be good for intaglio. Bronze is harder than copper and allowed us to get very fine detail in the images.
- Steel is even harder. It is etched using nitric acid and allows extremely high amounts of detail for engaving. Steel plates are used for the plates from which money is printed.