My favorite seams for making tunics is the flat-felled seam. This seam works well on straight or only slightly curved edges.
This type of seam is used on the sleeves of the Viborg Shirt which has been dated to around 1018AD.
I normally sew this together with the “flap” on the outside of the garment. It’s really up to you as to how you use it. I will note, I’ve found that if you put the flap on the inside of the garment you may find that you need to do a bit more hand finishing work right at the bottoms of the sleeves or at the very point of the gores. On the side with the flap this area will come out looking great. On the other side you may have some stray threads that you need to tuck in and possibly finish by hand.
1. Stack your fabric wrong sides together offset by 1/4 inch (ie, the bottom fabric should be 1/4″ further out than the top fabric)
2. Join these pieces together with a stitch line which is 1/4″ from the top fabric’s edge.
3. Open the fabric at the seam and fingerpress the seam allowance to get a firm crease at this first set of stitches. A firm crease here will help you sew the next part.
4. Fold the offset around the shorter side of the seam allowance and then pin this flat to the face of the fabric.
5. Sew down this flap (also called the fell). Try to keep your stitches as close to the edge (without falling off) as you can.
When I am hand sewing I will normally do the first line of stitches with a running stitch then I will do the second set of stitches with an overcast stitch. If the seam will be under pressure then you should us a back stitch instead of a running stitch. Normally on tunics none of the seams are under an undue amount of pressure so I don’t think I’ve ever had to use a backstitch for the first set of stitches.
A friend asked me: Don’t you worry about the fact that this is using up an uneven amount of seam allowance.
My response: I normally use this on tunics which have a lot of ease. Adding 1/8-1/4 to each side of the tunic has very little effect on the overall size of the tunic.