This was a bit of a revelation to me. Things have moved on so much in the sewing and knitting industry. There are so many ways to sew a zip. As a child I was taught to sew them by hand using a pinprick stitch. But I’ve since found there are better ways and better zips.
You need a special zip designed to not show once it’s attached. The other important thing you need is an invisible zip presser foot which has two channels in to hold on to the zip and to uncurl it as your machine sews a line of stitching really close to it. You can use an ordinary zipper foot but you have to tack the zip in place securely before sewing and you have to constantly push the presser foot against the zip as you sew. You can buy very cheap generic presser feet online and it’s definitely worth the investment, it makes life so much easier. INVISIBLE, CONCEALED ZIP, ZIPPER FOOT WITH TAIL SNAP ON, COMPATIBLE FOR BROTHER, JANOME, TOYOTA, NEW SINGER DOMESTIC SEWING MACHINES (Unless you have a 9 mm machine like I do and then you have to buy one specifically for that machine and that is VERY expensive, but actually, still worth it! Another difference in the invisible or concealed zip and any other you might have used is that you attach it to your garment first before sewing the seam, which is much easier.
So, first of all you need to finish the raw edges of your seam. I’ve only done the top bit which will run the length of the zip because I’m going to do a french seam which will all be enclosed.
The zip needs to be undone and placed face down 1.5 cm away from one edge and pinned in place.
Then sew along the zip with it inserted into one of the presser foot grooves.
When you near the zip pull, fasten off the threads and do the zip up before turning it over onto the other side of the seam and pin in place as you undo the zip.
Then sew down this side with the zip in the other groove of the presser foot.
Do the zip up and sew the seam below it, holding the zip out the way.
You now have a completed invisible zip which is concealed from the outside.
These pictures make it look like I only have one arm, but I do have two!