The Eagle's nest The Union! it must and shall be preserved.

The invention of lithography at the turn of the 19th century opened a new world for bird illustrators. It brought many advantages to the artist — ease of use, a softness of line, and a new freedom to effect bold designs with a wide range of light and dark tones. Most of the fine ornithology books of the 19th century were prepared in folio format with hand-colored lithographic plates. The lithographic process is one of flat surface printing from a design drawn on stone. It is based on the principle of the resistance of grease to water. There are no raised or cut portions, as there are in engraving and etching. The image is drawn with greasy ink or chalk on a smooth stone, and the rest of the stone is treated with gum arabic and nitric acid. The gum retains the lines of the greasy design, which repels the water used in printing. Special paper and ink, as well as a special press, are needed to produce the prints. First used for bird illustration in 1820, lithography was widely adopted by the best artists of the century. The technique was popular because the artist could draw his own illustration directly on the lithographic stone. Prints could be made from the drawing with no intermediary such as an engraver. Accurately reproduced and then colored by hand, the resulting illustrations gave the impression of original watercolor paintings.