In this final installment to the Bound Buttonholes series, tailoring expert Daryl Lancaster demonstrates how to finish the back of the buttonhole: You need to make a “window” in the facing that is behind the buttonhole.

Mark the window location

First, transfer the buttonhole location from the garment rather than the pattern. Fold the facing into its final position and press it well. Place the work on a cushioned surface, such as the ironing board, with the buttonhole side up. Push pins straight through from the right side at each buttonhole corner, to mark the facing area.

Next, place a rectangle of fusible interfacing over the pins. Use woven cotton interfacing, cut about 2 inches larger than the buttonhole opening in each direction. Don’t use knit interfacing, as it is not sturdy enough to support the window’s edge. Place the interfacing with its right side against the facing, that is, with the fusible side up. Pin this in place.

Draw a rectangle connecting the pins, with a marker or pencil that makes removable marks. Mark the rectangle around the outside of the pins, so the finished window opening is large enough to match the buttonhole size. Remove the corner pins.

Sew around the window

Open out the facing from the garment, and stitch around the marked rectangle. Use short stitches in thread that matches the interfacing color. Start on a long side (not at the corner), and pivot at each corner with the needle down. Remove the pins.

Cut the opening through the interfacing and fabric. Cut along the center, and clip into the corners, as you did when cutting the buttonhole opening.[LINK to “Completing the buttonholes”]

Push the interfacing through the facing to the wrong side. Pull it smoothly so no interfacing shows on the facing’s right…