Undertaking a work of art composed of 60 panels forced Lawrence to proceed methodically, yet the images appear spontaneous, full of movement and action. His choice of casein tempera (an aqueous medium based on milk proteins), a fast drying medium, suits his ability to capture the essence of a moment with limited means. Lawrence executed the series on standard-size 18-by-12-inch hardboard panels that he bought from a local supplier. With the help of his wife, he prepared the smooth side of the panels with a gesso of rabbit-skin glue and whiting. The preparation layer has a profound influence on the appearance of the paintings. Viewed under high magnification, a dense matrix of air bubbles is visible in the gesso, causing this layer to be very porous. As paint is brushed across the ground layer, it is drawn into a surface pitted with tiny voids, causing white dots to appear in the paint film (fig. 1).
As seen in this close-up infrared photograph (fig. 2), Lawrence traced only the larger sections of his drawings. The evenness and lack of hesitation present in the underdrawing for the knot in the sack indicate that it was made from a traced drawing. However, many of the details in his compositions, such as the paisley shapes on the sack, were added freehand with a graphite pencil or left until the painting stage. He later explained his rationale: “You can get some nice things going that way … you can trace a thing almost exactly as it is and it falls dead. It’s flat.” 
 Lawrence, interview with authors, Elizabeth Chew, and Shelly Wischhusen-Treece, The Phillips Collection, Washington, D.C., June 4, 1992.
Excerpted from Elizabeth Steele and Susana M. Halpine, “Precision and Spontaneity: Jacob Lawrence’s Materials and Techniques,” Jacob Lawrence: The Migration Series (Washington, DC: The Rappahannock Press in association with The Phillips Collection, 1993): 155-56.