A prick stitch is a kind of backstitch that is used to hand stitch facings and linings in such a way that they do not roll to the front of the garment. It is particularly appropriate for hems and seams where a reinforced stitch is required. It goes from right to left if you are right-handed, and left to right if you are left-handed. It can also be used for stitching a zipper by hand and is then known as "hand picking a zipper".
Machine-stitching vs. Hand-stitching
The main advantage of using hand stitching is that you are able to reach tight corners or go along curves where the sewing machine foot cannot be used. Of course, hand stitching is more painstaking and takes a lot more time than machine stitching. You will, however, find the time invested in hand stitching worthwhile because the garment will look that much better and more stylish than a machine-stitched garment.
Step 1 - Anchor Lining
Place your thimble on your middle finger. Once the lining has been attached to the fabric, anchor your thread to the right-hand edge of the fabric with the lining side facing you. Bring up the needle and thread at a point 1/4" to 1/8" from the top edge of the fabric.
Step 2 - Use the Needle
Insert the needle back into the fabric at a point 1/4" to 1/8" from the point above where you brought up the needle. The needle should pierce the lining and all of the allowances for the seam but should not penetrate the fabric on the outside. Bring the needle out at a point 1/4" to 1/8" from the point where you penetrated the fabric.
Step 3 - Repeat
Repeat going from right to left across the fabric in a straight line until you have finished. When you are finished the lining should be firmly attached but no stitches should show on the outside of the fabric. To help you keep a straight line, you can mark a straight line across the lining with a water-soluble marker. Because you are essentially pricking the outside fabric without penetrating it on every stitch, this is known as a prick stitch.
Hand-picking a Zipper
Hand stitching a zipper rather than machine stitching it ensures that the zipper sits nice and flat without any undulations in the fabric. Moreover, the stitch is just as strong and a prick stitch ensures that the zipper is not visible on the outside of the garment. The process is essentially the same as that described above, except that you will stitch from the top of the zipper to the bottom on the left-hand side, and then turn around and work your way up. You also need to be careful not to put your stitches too close to the teeth of the zipper, or your stitches may give way as the zipper is pulled up and down.
It is true that hand stitching a prick stitch is a painstaking and time-consuming process and that practice is needed to get it right. However, the enhanced look of the garment will more than repay you for your efforts.