Casting off stitches from the wrong side of work while purling. When you no longer need these stitches for example when making armholes, necklines and shoulders.
It`s important that the cast off edge is not to loose or too tight.
You can also use thicker needles when casting off to make sure the cast off edge is elastic.
Fig. 1: Purl 2 stitches.
Fig. 2: You now have 2 stitches on you right needle. Insert left needle in the stitch on the far right on the right needle.
Fig. 3: Lift this stitch over the other stitch (first stitch on the needle). Now there is only 1 stitch on the right needle.
Fig. 4: Purl 1 more stitch.
Fig. 5: You now have 2 stitches on right needle.
Fig. 6: Insert left needle in the stitch on the far right on the right needle.
Fig. 7: Lift this stitch over the other stitch. Continue like this until you have cast off all the stitches you needed to cast off. Whenever you want you can continue knitting over the remaining stitches on the left needle. Or continue casting off like this over all stitches.
Fig. 8: You have 1 stitch on right needle, this is the last stitch in your work.
Fig. 9:Cut the yarn and insert the yarn end through the loop (= the last stitch). You can now fasten off.
You can use this technique when you are done with your work for example when making a shawl and you need to cast off from the wrong side.