Oh, French seam. My first true love.
If you're looking for a neat, not-too-fussy way to seal off those raw edges, the French seam is for you!
French seams are a relatively recent development in the history of Western seam finishes. There's some evidence of French seams dating back to the 14th century, but up through the late 1800s most seamstresses enclosed their raw edges by flat-felling their seams. That is, if they bothered to enclose raw edges at all. Enclosed seams have historically been reserved for undergarments, where finishes had to withstand lots of, er, wear.
By the early 1900s, French seams were common enough that they were included in many sewing manuals. The French seam's growing popularity was likely tied to new home sewing technologies: the first Singers were manufactured in the 1850s, and French seams are less fussy to machine sew than flat-felled seams. Also, people at the turn-of-the-century were obsessed with see-through fabrics. With seam allowances suddenly visible, a clean finish became extra important.
When should you use a French seam?
French seams are most useful for thin fabrics, for anything that might ravel, and any time you want a neat finish. I use French seams in most of my patterns, including the Sweetheart Dress and the Wrap Skirt. I find the process soothing, and you can't beat a garment that looks as good on the inside as it does on the outside.
Here's how to French your seams:
I've read several ways to do French seams, and this is both the quickest and the neatest I've found. If you're using a pattern that has a 5/8" seam allowance, this method also doesn't require you to add anything to your seam allowance; you can use the pattern as-is.
Start with your two fabric pieces, right side up.
Lay them on top of each other, WRONG sides facing, and line them up along the seam edge.
Stitch the two pieces together using a 1/4" seam allowance.
Clean up the edges, and make sure your seam allowance is only 1/4". Mine usually ends up a little bigger, so I have to trim it down a bit.
Press the seam allowance open.
Fold along the seam so that the right sides of the fabric are touching and the seam allowance is enclosed. Press along the seam.
Stitch along the seam again, this time using a 3/8" seam allowance.
Your raw edges should now be completely enclosed in a tidy little pocket of fabric! Here is the french seam from the side:
To finish, press your French seam to one side, so that it lays flat against the main fabric.
And voila! A seam that looks just as good on the inside as it does on the outside!
Want more? Here are a few other tutorials on French seams:
Lauren on Wearing History, "Tutorials: How to Sew French Seams" (2012)
Haley Pierson-Cox on Make:, "Sewing 101: French Seams" (2012)
Jennifer Beeman on Grainline Studio, "French All Your Seams" (2014, includes straight and curved seams)
Christine Haynes on Craftsy, "Seam Series: How to Sew a French Seam Tutorial" (2013)
Angela Wolf on Craftsy, "How to sew a french seam step-by-step | Sewing Tutorial with Angela Wolf" (2015, video)