There are 2 main things that will instantly and dramatically raise the look of a hand-knitted garment from home-made to hand-crafted and these are:
1) Blocking! Pinning the individual pieces of a garment out to the specified sizes will not only even your stitches out, improve the drape and feel of the knitted fabric, but it will also make seaming that much easier.
2) Using Mattress Stitch on all seams that are suitable and to attach patch pockets will give your garment perfectly matched seams that are almost invisible too.
In the following tutorial, I aim to show you how to use Mattress Stitch on stocking/stockinette stitch and on garter stitch, but as you become more familiar with this technique, you will see that Mattress Stitch can be employed for a huge variety of seams. It really is the Shire Horse of the seaming world!
To begin, you will need a good length of the yarn that you knitted your garment with, a darning needle and some scissors. I have used a nice bright contrast - daisy yellow - so that you can see the mechanics of the stitching more easily. Any darning needle with an eye large enough to fit your yarn through is fine, and some scissors for trimming ends.
As you will see in the following series of pictures, the important thing to ensure a perfect seam is to be accurate. Making sure that the stitch on your right hand piece exactly matches the stitch on your left hand piece will mean that you won't end up with spare fabric on one side at the end of your seaming. I suggest taking time at the very beginning to avoid this, as mismatched stitches often don't become properly evident until you're nearing the end!
Beginning with a stocking stitch sample, place the 2 pieces to be seamed RIGHT SIDE facing in front of you - all mattress seaming is made with the right sides facing up. Next, starting on the right-hand piece, as in figure 1, pick up the bar 1 stitch in from the edge. If you insert your needle from bottom to top through the stitch to the back, you will be able to see the 'bar' between the v-shaped 'arrow' (figure 2)
At this point, it is important to ensure that you select the correct bar on the left hand piece. As you can clearly see in Figure 2, the right hand leg of the stitch which the needle is through, is leaning to the right. The corresponding stitch on the left hand side piece should be a left hand leg leaning to the left. In Figure 3 you can see these 2 sides with the 'ladder' of threads connecting the 2 halves - which, incidentally, is where Mattress Stitch derives its other name - Ladder Stitch from.
The next step is where the magic of Mattress Stitch really happens! Holding the bottom thread securely, pull firmly on the top thread (with the needle still attached) and watch the 2 pieces of fabric 'zip' together and the ladder disappear. As you can see in figure 4, the daisy yellow yarn now doesn't show, and the seam is almost invisible. You will also be able to see why it's so important to make sure you carefully select which 'bar' to pick up, as the neat join is comprised of the right and left legs of a 'v' - the normal shape of a 'knit stitch'.
Continue in this way, picking up an inch of stitches either side and then pulling them together. I find that if you pick up too many stitches and make the ladder too long, your thread can become tangled and not 'zip up' quite perfectly. See figures 5 and 6 which show progress up the seam and figures 7 and 8 illustrating the completed seam and wrong side view.
Figure 5 Figure 6
Figure 7 Figure 8
In the following section, the pictures show the same process but with garter stitch. The principle is the same, seam with right sides facing and match your stitches exactly on the left and right pieces to ensure a perfect join. The difference is that instead of picking up the 'bar' from underneath, you can see the bars or purl bumps on the surface of the fabric. This actually makes picking up the bars very much easier, but with garter stitch it is important to select a 'u-shaped' bump from one side and an 'n-shaped' bump from the other to give a seamless result (figure 9).
The yarn that you use to seam a garter stitch piece will need to be the same as the garment was knitted in, as it doesn't disappear so effectively as with stocking stitch (figures 10 and 11). You can see in figure 11 that the section at the bottom has a virtually undetectable seam, where the daisy yellow thread is evident in the top section.
Figure 10 Figure 11
Finally, in figures 12 and 13 you can see the finished seam and the wrong side.
Figure 12 Figure 13
The gaps at the top and bottom of the seam are easily joined with a few small secure stitches on the wrong side as you sew in the ends, and the result is a strong, almost invisible seam. Mattress Stitch is amazingly versatile and can be used to attach pockets or patches, as well as joining blanket squares or edgings. The only seam that I haven't yet been able to use it for, is for setting in sleeves, and for this I resort to back stitch. But who knows - perhaps I'll even give that a try with my trusty Mattress Stitch one of these days!
(posted by Max)