Stitch the First Seam
The following instructions describe a square being set into the opening left by two pieced-together diamonds.
With right sides together, pin one edge of the diamond unit to one edge of the square, aligning matching points. Hand-stitch the seam from the open end of the diamond into the corner, beginning and ending at the matching points and removing pins as you sew. Backstitch at the inside corner to secure, but do not cut the thread. Note: Keep seam allowances free of stitching. They are not sewn down as they are in machine piecing.
Align the Second Piece
Bring the adjacent edge of the square up and align it with the adjacent edge of the diamond unit. Insert a pin at aligned matching points, then pin the remainder of the seam line. Hand-stitch the seam from the corner to the open end of the angle, removing pins as you sew. Do not sew past the matching points at the end. Backstitch to secure the seam. Leave a short thread tail.
Press the Seams
Press both seam allowances of the set-in square toward the diamonds; press the diamonds’ joining seam to one side.
TIP: Sew a set-in triangle in the same manner as a set-in square.