French Seams are fabulous for lightweight fabrics in skirts and dresses - like the lining for my Royal Blue Pencil skirt. If you can get past the unnatural feeling you get when sewing the first seam with the right sides of the fabric facing out, then this is easy to master!
1. For slippery and thin fabrics like the silk habotai I'm lining a skirt with, I like to add an additional 5mm to the seam allowance before cutting out. For stiffer fabrics that aren't likely to get pushed into your feed dog whilst sewing a slim seam, this isn't really necessary.
After realising that my black thread and black silk habotai aren't really photo instruction friendly, I've pulled out some calico so you can actually see what's going on.
2. Align your fabrics with the wrong sides facing each other, and sew your seam with a 1cm seam allowance, or 0.75 if you're doing the usual 1.5cm seam allowance. Basically, whatever seam allowance you have allowed for on your fabric - divide that in two and this will be your allowance for your first and second seams. This is because we are effectively sewing two seams where we'd normally sew just the one.
For bulkier fabric, this is a good time to trim back your seam allowance to reduce bulk. I'm trimming this habotai back a little (3 or 4mm) just to prevent any loose threads coming through onto the right side when the second seam is sewn.
3. Iron along the seam you've just sewn to set the stitches:
then unfold your fabric flat and iron the seam to one side - as if you were ironing a dart flat:
Then fold the fabric over so the right sides are facing, making sure the seam line is right on the fold, and iron flat:
4. Back to the sewing machine, and sew another 1cm seam along the edge you just ironed - the raw edge of the fabric is now safely enclosed in your seam - no need to overlock or finish your edges. Iron flat and you're ready to go!
The end result? Your fabric edge is safely tucked inside it's own seam: