Very few copies of books could be made, resulting in a very high per book cost and very limited sales. Copper plate engraving is primarily a linear process, as only the lines which are cut into the metal will hold the ink and be printed. Shading could be added by crosshatching lines of varying width, but the lines remain visible. The aquatint method was an attempt to produce gradations of tone in the printing process. Artists were attempting to imitate the effect of a watercolor was, particularly useful in producing landscapes.
Aquatint is produced by dusting the copper plate with a resin and heating the plate.
As the grains of resin melt, they produce an irregular pattern of a dark network surrounding small white patches of resin. When acid is applied to the plate, it will etch only the spaces around the resin, resulting in an overall textured pattern. Watercolor was then applied over the printing to achieve the colored image. Aquatint came into use in the mid-eighteenth century and was used extensively from the 1770s until the 1830s. The books most noted for aquatint engraving during the beginning of the nineteenth century were caricature or genre works and books of landscapes.