One of the more inventive and interesting sorts of tonal etching processes, where one uses powdered asphaltum suspended in alcohol as the acid resist. Because of the specific chemical natures of each, the asphaltum does not dissolve in the alcohol, and the individual particles become adhered to the plate as the alcohol dries. The resulting covering on the plate is granular as opposed to uniform in nature, distinguishing it from most other etching processes.
The spirit wash is one of very few printmaking techniques that allows one to create a range of tonal values using only a single bite. The concentration of asphaltum particles in any given spot on the plate will dictate how much or how little of the plate will be eaten away in the acid. By carefully pushing around the solution and adding more concentrated asphaltum to less concentrated areas (and vice versa), one can create a wide range of tones. All of this must be done, however, within the context of the wet medium, and as such one has somewhat limited control over exactly what the final image will look like. The wash tends to dry in different waves, creating borders of thicker asphaltum resembling salt rings around droplets of dried salt water where the solution pools.
We have the multitude of drunken artists in the world to thank for the name ‘spirit wash’. While the technique works perfectly well using plain old denatured alcohol (a common staple in any good printshop), it has come to be believed that using high quality distilled liquor (whiskey, vodka, rum, et cetera) will magically enhance the quality of the resulting image in a way that no ordinary alcohol could possibly match. Regardless of whether or not that is true, it does make for an excellent excuse to bring booze into the studio, which I daresay is all that really matters.