What is the difference between a French seam and a Mock French seam?
You can distinguish a mock French seam from a regular French seam by identifying the presence of a topstitch within the seam allowance: A mock French seam features a topstitch next to the folded seam allowance edges. A French seam has no visible topstitching within the seam allowance layers but rather features a seam along the seam allowance edge. Here is a more detailed breakdown of both of these seam finishes:
If you take a closer look at the wrong side of a french seam, you will notice a seam running down the edge of the folded seam allowance. The only stitch-line visible is the seam stitch and no other topstitching is present.
In a French seam application, the seam allowance is enclosed by applying two separate seam stitches which surround the raw fabric edges. The seam is initially stitches at half the seam allowance with with wrong sides touching (which is the opposite of conventional seams), then the seam is flipped such that the fabric face sides are touching and the final seam stitch is applied to permanently encase the seam allowance edges and complete the seam.
If you take a closer look at the wrong side of a mock french seam application, you'll see a topstitch running a long the folded seam allowance edges- no seamline will be present along the folded seam allowance edges.
As opposed to a classic french seam application, a mock french seam is initially aligned and stitched as you would any conventional seam fabric face sides touching and following the seams designated seam allowance. It is after the seam is stitched that the seam allowance layers are folded to resemble a french seam. The folded seam allowance edges are carefully topstitched together (along the open edges) to permanently seal the raw fabric edges.
When sewing a mock French seam, the easiest way to fold the seam allowance layers evenly and keep them perfectly stable during the topstitching process is to iron each layer individually folded at the seam distance throughout (usually with fabric raw edges aligning at the seamlines), then iron the folded edges together to secure and crease the final alignment. You can use pins or a temporary hand basting stitch to keep the seam allowance layers perfectly aligned in the topstitching process.