Sol LeWitt created Wall Drawing 340 during a period of experimentation with basic geometric shapes. His formal vocabulary included what the artist referred to as ‘primary’ shapes – circle, square, triangle – and ‘secondary’ shapes – parallelogram, trapezoid, and rectangle. While earlier drawings, such as Wall Drawing 295 (also on display at MASS MoCA) depict these shapes in outline only, in Wall Drawing 340 the shapes are delineated by straight parallel horizontal and vertical lines (the most basic elements of LeWitt’s vocabulary). Later, the geometric forms became even bolder as LeWitt began entirely filling them in with solid colors.
As LeWitt’s formal and material vocabularies grew and changed, his use of color became bolder. His earliest wall drawings, which were drawn in graphite and colored pencil on white wall, appear faint and ethereal. In the mid-1970s, he started to create drawings with primary color and black backgrounds. The draftsmen drew on the colored walls using white crayon or chalk. By 1980, when LeWitt created Wall Drawing 340, he had begun using primary colored crayons. The drawing's instructions call for the draftsmen to draw in crayon on top of red, yellow, and blue backgrounds. This process of layering one primary color over another creates secondary hues. In the drawing LeWitt depicts all possible combinations of primary color crayon over different primary color backgrounds.
The crayon wall drawings are executed on walls with an orange peel-like texture, which allows the crayon to stick to the wall. It only adheres to the raised parts of the surface; thus the light shines through the crayon, hitting the surface of the wall and revealing its texture.