The Mattress Stitch joins two knitted fabrics neatly together creating an invisible seam. Used for seaming vertical stockinette stitch row by row, this method is best suited for side and sleeve seams. The examples shown below demonstrate how to use the mattress stitch to sew together the side seam of a child's sweater (the "Avery" sweater by Bee's Knees Knits - pattern and yarn are available at the shop).
The first step is to block the knitted pieces so that the edges will not curl making the fabric easier to sew. To block, I soak my knitted pieces in lukewarm water with a small amount of Eucalan (a very mild wool soap) for about 10 minutes or so. After gently removing the excess water by rolling them in a towel, I lie the pieces on foam (use anything flat that you can stick pins into). Then I smooth the pieces out to the measurements specified in the pattern and pin the edges to secure. Once dry, the pieces will lie flat and are ready to sew.
Lay the blocked pieces side by side with the right sides facing you (below). The Mattress Stitch is done on the right side of the work making it easy to see where you are going.
First locate the edge stitches. They are usually rather uneven and appear to almost face sideways. The beauty of the mattress stitch is that it makes these unruly stitches disappear.
Next, locate the horizontal bar that runs in between the edge stitch and its neighbour. If you pull the edge stitch slightly away from the stitch next to it, you should see the bar running in between. To do the mattress stitch, you weave yarn under a bar from one side and then run it through the corresponding horizontal bar on the other side. This will be explained next.
Now the seaming begins! Take a blunt needle and thread it with your working yarn. You will need enough yarn to finish your seam. For demonstration purposes, I used a contrast colour so it would be easy to see. Insert your needle under a bar.
Next, insert the needle under the bar of the corresponding row on the other piece.
Continue working back and forth, inserting the needle under the bar on one piece, then the other, while trying to work matching rows (as close as you can). Don't worry about tightening up the yarn after each insert. I always work several rows first. Then just gently pull on the yarn and the pieces should join smoothly. Don't pull too tightly or it will pucker.
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