“Stay Stitch inside the seam allowance” is a fairly common instruction in patterns. Generally, stay stitching is used to make certain that the fabric of a garment will not stretch out during the sewing process. It’s also a dandy cheater hem, which will fray (but only so far – it’s a controlled fray). Sometimes, that’s exactly the look you want.
Seam Allowance Required: Variable
For stay stitching that is done to prevent stretching during the sewing process (like when you have directions that say to stay stitch before sewing), you’ll want to use a long stitch length and sew just inside the seam allowance. To use stay stitching as a hem, use a normal stitch length.
Sometimes, things really are that easy. Well, almost. If you’re trying for a frayed-looking hem, you might want to start teasing out threads from the seam allowance to get the fraying started. In theory, you could always wash it a zillion times, but that trick never works when I want it to. Also, if your goal is to make it look like the hem is just frayed, it’s a good idea to match the thread color to the fabric color.
Now, the obvious question is: Why wouldn’t I just let the darn hem fray? Well…. Let’s say you’re making some sort of rough peasant-y beggarly skirt, and you want it to look completely wretched, with a hem that looks like the dog’s been chewing on it and a few artistic holes. You want to make it out of a good, rough woven cloth – something just finer than burlap. And you don’t want it to self-destruct while you’re wearing it, and are hoping it will last for a while. This is where stay stitching as a hem is brilliant – you can stitch whatever crazy old looks-like-an-EKG style hem you want, then cut it. It will self destruct in a nice, controlled manner and never go past the line of the stay stitch. You could even stay stitch around a few well-placed holes, then cut the threads in the middle and let them fray out. Voila! You’ve created the wash-and-wear beggar.