Clamshell Quilt-Edge Finish

A decorative edge finish can elevate a quilt from excellent to extraordinary. In this tutorial, we will learn how to create a clamshell quilt edge finish. Watch the video or follow along step-by-step below.

A clamshell is half a circle. If you took a circle with a 1” diameter and divided it in half, you would end up with a clamshell that is one inch wide and half-an-inch high.

To draft a clamshell pattern, draw a semi-circle of the desired size. Combo circle templates are very handy for drawing circles, or you can use a compass. If you’re handy with your computer, many programs will draw circles and half circles in any size. Add two straight lines to the semi-circle a quarter of an inch long. This will be the seam allowance for the clamshell.

For my project, I’m making clamshells in three sizes: three-quarters of an inch; half an inch; and three-eights of an inch. Trace the clamshell shape, plus seam allowance, onto the wrong side of a strip of fabric. I made my strip long enough so that I could fold it to make two layers. Or, you could cut another fabric strip for the second layer instead.

Set up your sewing machine for a small straight stitch. I reduced the stitch length on my machine to 1 mm. Place the two layers right sides together and stitch on the marked lines.

Cut out the clamshell close to the stitching.

Now, turn the clamshell right side out. This will be a challenge for small-size clamshells, so here’s my trick.

Find a small tubular object that will fit inside the clamshell opening. It could be a straw or an electrical wire connector or a drywall anchor, which is what I’m using. Then find a blunt tip instrument that will fit into the tube. A crochet hook could work or I’m using a tool called “That Purple Thang”.

Insert the tube into the clamshell, then push the clamshell fabric into the tube using the blunt instrument. Remove the tube and continue pushing the fabric until it is completely right side out.

To give the clamshell a good press, I made a heat-resistant Mylar template. The template has the same half-circle shape at the end and a long edge to hold onto. I dip the fabric clamshell in water, to soften the fibers and remove any fabric markings. Insert the Mylar template, smooth the curved fabric edge, and press.

The project that I’m working on will finish as a circle. I lined up the raw edges of the clamshells with the circle I had drawn on my background fabric. For a quilt with a straight edge, line up the clamshells with the outside edge of the quilt or border strip. Sew the clamshells with a quarter-inch seam allowance.

For my circle project, I cut a piece of batting the finished size of the quilt. For a larger quilt, the batting could be trimmed after quilting right close to the outside edge.

Press under the seam allowance of the backing fabric.

Turn the clamshells to the outside edge and cover the raw edges with the backing fabric.

Hand stitch the backing fabric in place.


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