Sewing: Grading and Understitching

For the purposes of this article, we are talking about an edge seam. In a garment, you might have an edge seam on a collar, a pocket flap, a front opening on a jacket or blouse, an armhole, or a neckline. The thing that characterizes all of these components is that there is a separate sewn-on facing that is folded back, putting the seam at the very edge of that component. In an ideal world, only the top side of the component is visible to the public - the underside is not visible.

However, it is difficult to do the appropriate pressing to make sure that just the top side is visible.

Grading

Let's move into pictures and talk about grading. Here is a sample, with a standard 5/8 inch or 1.5 centimeter seam allowance. In this sample, the darker fabric is considered the right side, and the lighter fabric is considered to be the facing.

The following two photos are a bit exaggerated, but in both of them you can see the other side of the fabric peeking through:

But that fabric peeking through to the other side is not the only issue. If you run your finger about 5/8 inch from the edge seam, you can feel a very definite cliff underneath. If the fabric has any significant thickness, that cliff can be quite prominent, and it will be visible in the garment.

Hmmmm - someone needs a manicure!

The answer to the cliff problem is to do some grading. First, trim the seam allowance of the facing to about 1/4 inch. Then, trim the other seam allowance to about 3/8 inch.

Usually I tell students to trim the second seam allowance about halfway between the two cut edges. Sometimes those who are new to sewing will not be able to cut the first seam allowance a nice even 1/4 inch. Sometimes they don't even recognize the 1/8 inch extension required for the second cut. So as long as the second trimming is halfway between the first trimming and the original seam allowance, they will be able to do a good grade.

Understitching

First, press the graded piece. Press both seam allowances to one side, such that the longer seam allowance covers the shorter one. They will be on top of the facing portion.

Second, sew those seam allowances to the facing, fairly close to the original seam.

With the understitching completed, it now is really hard to make the facing side show on the public side of that edge seam. This photo of the end of the sample shows that the understitching is almost forcing the facing away from the fold.

At this point in the workshop, I usually challenge my students to TRY to make the facing side visible from the public side - and they cannot! And that is Magic #2.

Here is a photo of the facing side - the underside - see the thin hair of public fabric peeking over.

And on the public side, there is no facing showing through at all.

Grading and Understitching Curved Seams

The armholes of sleeveless garments and curved necklines are typical areas for curved edge seams. The only significant difference from a straight seam is that there will have to be some clipping. And the pressing and understitching can be a little fiddly. To start with, here is a photo showing the grading of a curved seam. In this sample, the yellow is the public side, and the pale green is the facing.

After grading, clip the seam allowances.

Here is the first fiddly part: the pressing. Lay the piece on the ironing board with the facing side up, lift the facing, and press the facing over the seam allowances, BUT only put the iron about 1/4 inch onto the facing. All that is needed is for the seam to be pressed, not the facing.

Now understitch. This is the other fiddly part. The facing and the main fabric will have a lot of curvature in them. Just make sure that the fabric is nice and flat for about an inch ahead of where you are sewing. Where you come to clips, just sew over them as they lie flat - do not try to close them up.

The understitching is done:

And after the facing is folded to the wrong side, here is the the result - you can see a thin strip of the public yellow peeking over the facing.

And that's a good thing!

Conclusion