Pinking! If you're looking for an authentic midcentury finish for your seam allowances, pinking is the way to go.
Pinking shears as we know them today were patented in the early 1930s by Samuel Briskman of the American Pinking Shear Corporation. By the early 1950s, his distributor J Wiss was selling upward of 500,000 pairs of pinking shears every year!
With sergers still prohibitively expensive, pinking was the most economical way for home sewists and professional seamstresses to neatly keep seam allowances from raveling.
You can read more about the history of pinking here.
To Pink or Not to Pink?
Pinking works best on stable woven fabrics, and it's most useful for fabrics made of natural fibers, since these tend to ravel more than synthetics. The zig-zag or scalloped edge created by pinking shears reduces ravelling by shortening the fibers along the fabric edge. You don't need to pink knit fabrics, since these don't ravel.
Midcentury sewists used pinking primarily in casual, everyday garments; more time-consuming finishes like French seams were reserved for more formal pieces or unstable fabrics.
In contemporary sewing, pinking is a less-pricey substitute for serging, and it's a good alternative to a zig-zag stitch if you are sewing on a straight-stitch machine. I pink my seams anytime speedy construction is more important than creating a couture finish.
Here's how to pink your seams:
Start with two pieces of fabric, both right side up.
Line up the fabric at the seam edge, right sides together.
Stitch the seam with a 5/8" seam allowance.
Trim the seam allowance with the pinking shears. 1950s instructions usually say to trim as close to the edge as possible, so that a fair amount of the seam allowance is preserved in case you want to alter the garment later. I usually pink down to 1/4" to reduce bulk along the seam.
Press the seam allowance open and carry on with the rest of your pattern!
Want more? Here are a few other tutorials on pinking goodness:
Mary Ray in Threads, "Keep These Seam Finishes in Your Bag of Tricks" (2010)
April Henry on Oliver + S, "Pinking Finished Seams" (2010)
Shannon Dennis on CraftStylish, "How to Pink Your Edges" (2008)