Every scientific illustration begins with a rough sketch - usually several sketches. Many details must be discussed between the artist and scientist before a final drawing can be done, and several additional preliminary drawings must be prepared in order to work out aesthetic details, such as shading and other aspects. The Kellogg Illustration Collection provides many examples of this process. (See Pantograph section for more details about how Prentice prepared his preliminary drawings.)
The pen and ink thick/thin line technique
Pen and ink line illustrations are clean, crisp, clear, and inexpensive to reproduce, making them ideal for scientific illustrations. Sydney Prentice was a master of the pen and ink thick/thin (eyelash) technique. This is a very difficult but beautiful technique, and is especially well-suited for drawing vertebrate specimens because of the grain inherent in bone.
To execute the thick/thin line technique, an artist must use a dip pen with a flexible nib loaded with ink. Then, a single line is made which can vary from thick to thin depending on the amount of pressure placed on the pen while drawing the line. With this technique, it is possible to create a complex system of lines to denote form, structure, texture, light and shade using a very high contrast black/white medium. No gray is present; only the impression of gray created by line.
Ink drawings are made on a heavy drawing paper, such as Bristol Board.
Now, an artist could do the same technique with a computer and proper software, drawing tablet, or monitor.