Every artist had their own technique for creating preseparated art. For their book The Terrible Troll Bird Ingri and Edgar d'Aulaire went to the extraordinary length of creating the key plate illustration on lithographic stone.

Lithography dates back to the late eighteenth century. It relies on the principle that oil and water do not mix. Traditionally, the artist would work on a very flat piece of porous limestone using beeswax or other greasy substance. The stone is then etched through a chemical wash involving a mixture of gum arabic and nitric acid to fuse the illustration with the stone and make the non-image areas hydrophilic. Before printing, water is applied to the stone and is absorbed by areas that do not bear illustration. Oil based ink is then rolled onto the stone; it adheres to the illustrated areas but is repelled from the wet non-image areas.1 This ink can then be transferred to a sheet of paper to create a print. Note that this print is the reverse of the illustration on the stone. Lithography is a type of planographic printing, meaning the printing surface is flat.2

Paul Zelinsky and Ava Weiss explain stone lithography

Modern offset lithography printing presses use the same principles with a few advancements that allow for rapid reproduction. The stones are replaced with metal plates wrapped around cylinders and etched using a photochemical process. The ink is transferred to a rubber offset roller before printing on paper to improve the quality of the final print and reverse the image a second time.3 Offset lithography is still the most common method of commercial printing.

The d'Aulaire's work was a hybrid of old and new techniques. They used traditional techniques to create the key plate images on lithographic stones, but the stones were not used in the mass printing of the book. Instead, the lithographic print created by the stone was reversed by the camera person and photographically etched on a metal plate for use in an offset lithographic press. Rather than preparing stones for each color in the book, the artists created red, blue, and yellow color separations on acetate overlays. The final result is a beautiful piece of color artwork.

1. Lawson, L. E. Offset Lithography. London: Vista, 1963. Print. 23-24 

2. Stone, Bernard, and Arthur Eckstein. Preparing Art for Printing. New York: Reinhold, 1965. Print. 26 

3. Pitz, Henry C. Illustrating Children's Books: History, Technique, Production. New York: Watson-Guptill Publications, 1963. Print. 163-164