A keyhole opening is a very pretty feature to have in the back of a blouse or dress. The Park Lane Dress and Blouse pattern features a keyhole opening with button and loop closure and I thought it would be helpful to reproduce that section of the Park Lane instructions here for anyone who wants to add a this into a different pattern. I'm thinking in particular of the Carnaby Dress, where the keyhole could directly replace the centre-back zip feature. I opted for this modification in my recent Carnaby peplum top hack. These instructions only work on a pattern with a centre-back seam and relatively high (i.e. not v-shaped nor plunging) back neckline, and assume that the neckline is finished with a facing.
Create the opening and finish the centre-back seam:
Firstly, work out how deep you want your keyhole to be. In the case of the Carnaby, it makes sense to use the notches that mark the base of the zip for the bottom of your keyhole. With another pattern, simply measure down from the neck (taking into account the neckline seam allowance) and make a small triangular notch into your CB raw edges where you want the keyhole to close.
Finish the raw edges of the centre back on each back bodice piece with an overlock or zigzag stitch. If you've lost sight of the notches under the overlocking, make a chalk match or a tailor's tack.
Press under 0.5cm/1/4 inch down the centre-back edge of each back piece. Stitch this narrow folded hem in place on both back pieces, as close to the raw edges as possible
Now match the two back pieces down the centre-back, right sides together, and pin from the notches down to the bottom hem. (Although the notched raw edge has been folded back and stitched in the steps above, you should still be able to see the notches.) With a 1cm/3/8 inch seam allowance, stitch from the notches down to the hem.
Press open the stitched centre-back seam. Above the notches, where the two halves of the back are still separate, press over the narrow hem another 1 cm on each side, in line with the seamline below.
From the right side of the garment, top-stitch around the centre-back opening at around 8mm/3/8 inch in from the edges, pivoting at the bottom of the opening.
Create a rouleau loop:
Cut a rectangle of fabric 5 x 3 cm, on the bias. Fold it in half lengthways, right sides together, and press. Stitch down the length at about 0.5 cm/1/4 inch from the folded edge to create a narrow tube. Trim the raw edges to close to the stitching line.
If you have a loop turner use it to turn your tube the right way out. If you don’t, an alternative method is to secure a piece of thread to one end of the tube, through just one layer (not closing the tube) and then tie the other end of the thread to a needle (preferably one that isn’t too sharp). Then guide the needle through the tube and out the other side. Tug on the thread until it starts to pull the other end of the tube inside itself, and then continue to pull until the tube is completely the right way out.
Make a loop with your rouleau tube big enough to go over your button and secure the loop with a few hand or machine stitches just holding it together. Trim off the excess ends of the tube, leaving tails of about 1 cm/3/8 inch.
Attach the facing and the rouleau loop:
Stitch the neckline facing in place. There should be some excess at the centre-back.
On the wrong side of the garment, with the facing pushed up and out of thee way, place the button loop in the right-hand centre-back upper corner, making sure enough loop peeks out to the right side to go over your button. Keeping the facing out of the way, secure the loop in place by stitching over your existing top-stitching line, back and forth a few times. On the right side, the loop will peek out from the upper left-hand corner.
Now turn the neck facing to the inside and press. At the centre-back, fold the excess facing under so it is tucked between the facing and the blouse, and hand-stitch it in place.
Stitch a 12mm/1/2 inch button in place on the right-hand centre back.
And voila! You have a gorgeous keyhole opening in the back of your garment.