Assemble the Sashing Units
1. For accurate sewing lines, use a quilter's pencil to mark a diagonal line on the wrong side of 142 of the red print 2-1/2" squares. (To prevent the fabric from stretching as you draw the lines, place 220-grit sandpaper under the squares.)
2. Align a marked red print 2-1/2" square with one end of a black batik 2-1/2x8-1/2" sashing rectangle (see Diagram 1; note the placement of the marked diagonal line). Stitch on the marked line; trim away the excess fabric, leaving a 1/4" seam allowance. Press the attached triangle open.
3. In the same manner, align a second marked red print 2-1/2" square with the opposite end of the black batik 2-1/2x8-1/2" rectangle (see Diagram 1, again noting the placement of the marked line). Stitch on the marked line; trim and press as before to make a sashing unit. The pieced sashing unit should still measure 2-1/2x8-1/2", including the seam allowances.
4. Repeat steps 2 and 3 to make a total of 71 sashing units.