Aquatint

Like etching, also aquatint makes use of acid. The plate is immersed in a dilute acid solution, which marks the matrix.
The effect is similar to watercolour, although the procedure is more similar to etching.
The typical granulation of this technique is obtained by applying bitumen grains onto a heated metal plate. The grains melt adhering to the plate and create a coat, whose density depends on the applied amount. Aquatint is a tonal technique. Unlike etching or burin, where a series of arranged marks are made to obtain a tonal effect. In this case, it is given by the amount of bitumen applied onto the plate and the depth of biting. Both colophony (Greek pitch) and bitumen (ground asphalt) can be used to obtain the same result.
After heating the plate, the materials described above are applied onto it, which adhere to the metal while melting. Then the spaces to be left white are covered with a special protective paint and all is dipped in acid. With this system velvety effects and tonal shades are obtained.