Fast Corners
Mark a diagonal line corner to corner across the wrong side of a dark A. Place the A on the corner of a C, right sides together, aligning the edges. Stitch on the marked line. Trim the seam allowance to 1/4". Open the A patch and press. Repeat for the diagonally opposite corner using a light A (Fig. 1). Make 80 units like this. Make 80 as in Fig. 2, reversing the direction of the seams.
Use the same method to construct the sash units, stitching 2 A's to adjacent corners of E's for end sash units and 4 A's to all corners of E's for the center sash units, noting color placement on the quilt.