A design technique the quiltmakers employed to master the tricky nature of corduroy was to arrange leftover strips to create large color blocks. Nellie Mae Abram's bold six-block “Housetop” variation offers a brilliant example. Using only three colors of corduroy—gold, avocado green, and brown—she expertly silhouetted blocks against blocks to create powerful positive and negative spaces. Two tiny pieces of contrasting color inserted near the “frontier” between the upper and lower halves of the quilt enliven the relationship between the the two dominant zones. In contract to the zippering effect of the small pieces, variations in block edges at the top and bottom of the quilt make for visual forces that pull the quilt’s to large halves apart. Additional revisions of the four outer rectangles introduce diagonal stress into the composition. Several types of movement—centripetal (toward the center axis), centrifugal (away from the central axis), and three-dimensional—seem to be taking place simultaneously, requiring the eye to “remake” the composition each time a new rectangle becomes the object of focus.