It gave me such good results that I wanted to share it with you, however when I went back to find it again I couldn't, so I decided to write my own.
Start by applying a strip of fuseable interfacing to your zip opening. The strip needs to be slightly wider than the seam allowance so for a 5/8" seam allowance 3/4" is about perfect.
The next step is where we really deviate from the way most people insert invisible zips. We're going to sew the seam below the zip. Make sure you back stitch to secure the top of the seam below the opening. Once you've done that, set your machine to it's longest stitch length and machine baste the zip opening closed.
In the photo below I've marked the transition between the basting stitches and the finished seam with a pin.
Press the seam open, then pin the zip in place face down over the basted opening. Make sure you only pin into the seam allowance, not through the main fabric.
Now baste the zip in place and remove the pins. Again, make sure you only attach the zip to the seam allowance. Turn the piece over to the right side and remove the machine basting from the zip opening.
To stitch the zip in place you can use either an invisible zip foot or a normal zip foot, whichever you prefer. I've used my invisible zip foot in the following photos.
Open the zip and position it under the foot so that the machine needle stitches into the zip tape and seam allowance of the fabric.
If you're using an invisible zip foot you may need to lift it slightly to get it to run smoothly over the little plastic stopper at the top of the zip. Stitch as far as you can go, then backstitch to secure the bottom.
Repeat on the other side.
Secure the bottom of the zip tape to the seam allowance on each side, either with a few hand stitches or machine stitches. Remove the basting stitches that held the zip in place while you machined it in.
Sit back and admire your beautifully inserted invisible zip!
I will admit this is not the quickest method I've used, but I think it's the best! I've inserted zips into 2 dresses using this method and they are both perfectly invisible.
I hope you've found this tutorial useful. If you try it, leave me a comment and let me know what you think to it. I know I'll be using this method from now on.