Press open, press toward one side or the other, spin the seams… is there a rhyme or reason to any of these directions??

Seam allowances are just as important in quilting as the cutting and the quilting.

Most of us know that the 1/4″ seam allowance is just as important as cutting to ensure our blocks are the right size when finished. There are tapes, magnets, and special feet to achieve 1/4″ seams, but there are a few more tricks you may want to know.

We know that 1/4″ is the formula used to calculate the cutting sizes and piecing sizes. But it does not take into account the fabric.

When you fold the fabric for a seam allowance, the fabric isn’t perfectly flat. The threads of the fabric and the threads in the seam add bulk to the seam making it a little “fatter.”

This inaccuracy can be minimized with a few simple tricks. The first is to use a thinner sewing thread. The second is to use a “scant” quarter inch. This means the seam is two or three threads smaller than 1/4″. This accounts for the thickness in the fold.

Another trick is to press the seams and then place a pressing block or clapper on the seam to flatten it as much as possible. The clapper holds the heat and adds pressure so that the seam will stay flatter.

Since flat seams are the objective, pressing the seams open seems like it would make it flatter. Pressing open means that each seam allowance is pressed back onto itself. This also minimizes any shadows.

Shadows occur when the seam allowance of a dark fabric is visible through a lighter fabric. Quilt judges take these seriously. Picky people fret over them. And as much as I am a laid back quilter, even I get distracted by them.

So if open seams hide shadows and make flatter seams, why not use them all the time?

There are two downsides to open seams and they are related. An open seam is weaker. The space between the two folds is held together just by the sewing threads. This means that any stress or strain can more easily rip the seam open. Or it can allow the batting to poke through the seam.

On the other hand, a seam that is folded to one side is stronger. There is always a layer of fabric reinforcing the seam.

Let’s tackle the first issue – the shadow. Shadows are eliminated by making the dark seam allowance slightly narrower than the light seam allowance. This ensures the light fabric always covers the dark, even with the extra fabric needed for the fold.

Some quilters trim the dark seam allowance after sewing. I make sure the light overlap is longer before sewing. Of course, this also means I need to measure and trim a little more often with traditional piecing.

The second issue is the flatness of the seams. There is a valuable trade-off. Seams pressed to one side create a ridge (less flat). This ridge can be very helpful when aligning seams.

These ridges act like puzzle pieces when placing pieces right sides together. They nest together. That nesting creates a perfect intersection of seams.

To minimize the “bump” at the seam intersection, arrange the seams so they rotate around the intersection point. This is called spinning the seams. It reduces the bulk where the seams meet.

So imagine an eight-point star. Spinning that seam reduces the bulk or mountain where those eight seams meet. Whoever quilts your top will be so glad you did.

So which way should you press your seams if you have to pick one side or the other? Usually, a designer will have you press toward the darker fabric, unless it will prevent you from spinning the seams later.

Now you know the secrets of seam allowances. Regardless if your pattern specifies how to press your seams, you know how to improve your quilt without their help.