This high fashion buttonhole treatment is a perfect solution when fabric is very dimensional and a machine stitched buttonhole that's not perfect can ruin a beautifully sewn garment.
1. To minimize the front bulk use a jacket pattern with a cut-on facing. That means the facing is one piece with the pattern and is just folded under at the vertical front edges.
2. Draw two lines perpendicular to the center front line.The first line passes through your bust point and the second line is 8-inches below the first line. These lines will become the horizontal seams that house the slot buttonholes. The seams can be sewn on the jacket front only or completely around the front and back. If the seams are to be featured around the circumference of the garment, mark the front pattern piece first and then align the back side seam with the front and continue drawing the horizontal seam lines in the same position so the front and back match.
3. On the horizontal lines draw buttonhole placement lines on each side and equal distance from the front fold line to position the buttonholes. Mark the ends of the buttonhole. These marks indicate the stitch termination points when sewing the horizontal seams together. In the example pictured the buttonholes are exactly 1-inch long. Make a sample with your fabric to see if the buttonhole size is right so the button can pass easily through the slot once completed. The thickness of the garment fabric and interfacing can make the finished buttonhole smaller than desired.
4. At the neckline stitching line, mark the buttonhole the same distance away from the front fold line as the others. Mark both the garment front and facing. If it is difficult to mark the stitch termination dots along the collar stitching line, wait until the collar is pinned to the garment,. Then mark the stitch termination dots on the collar following the their placement along the garment front.
5. Cut the pattern piece along the horizontal seamlines. Tape a strip of 1/8-inch graph paper to each new cut edge of the pattern piece. Match a vertical line on the graph paper to the center front fold line. Draw the grainline onto each section of the graph paper, also the center front fold line. Draw a line ⅝-inch away from the original tissue pattern for the seam allowance. Using graph paper makes adding seam allowances more precise and speeds up the process. Graph paper can also be used to lengthen a garment quickly.
6. Redraw the buttonhole stitch termination lines on both sides of the front fold. To assemble the garment sew the horizontal seams first. If the garment has horizontal seams around the circumference, sew the side seams first and then the horizontal seams to keep the horizontal seams strong and uninterupted. When you sew these seams, stitch up to the stitch termination point, back tack, jump over the buttonhole section to the second termination point, back tack and start stitching again. The point is to leave the buttonhole open between the stitch termination points. Press the seam allowances open and assemble the garment as usual.
Match the slot openings on the garment front and facing.
Slip a small length of 1/4-inch wide Steam-a-Seam 2 between the garment and facing layers on the seam allowance . Press to fuse the sections of the garment and facing together.
Once the garment is sewn, Ready-to-Wear top stitches the seam allowances about a presser foot away from the seam.