How do I unpick an overlocked seam?

Do not attack it with a seam ripper stitch by stitch. Pull the needle threads instead, and the whole thing comes apart.

Identify the threads. In an overlock stitch, the needle threads form the straight rows of stitching set in from the edge. The looper threads form the loops wrapping the raw edge. The needle threads hold everything; the loopers merely wrap.

The method. Find a needle thread at one end of the seam — starting where the chain is, or at a point where you have snipped it. Slide a pin or a needle under it and lift a loop. Pull steadily. On a four-thread seam there are two needle threads, so do each in turn. As they come out, the looper threads lose their anchor and the whole overlocked edge lifts away as a chain.

If the thread will not run, snip a needle thread every few centimetres along the seam. Then the sections pull out easily. This is quicker than fighting a thread that keeps breaking.

Use a seam ripper only to snip individual needle threads, never to saw along the edge. Sawing cuts fabric, and there is no seam allowance to spare — the overlocker trimmed it.

Accept the width you have lost. An overlocker cut the allowance when it sewed. Unpicking gives you the fabric back but not the trimmed strip, so the piece is now narrower and any re-sewn seam sits further in.

Contrasting looper threads help enormously on a test garment, because you can see exactly which thread is which.