In sewing, a seam is the join where two or more layers of fabric, leather, or other materials are held together with stitches. Wikipedia.
Those stitches can be either made by hand or by machine (that, in turn, can be a sewing machine or a serger/overlocker, that also grades and finishes seam allowances in one single step).
In most seams, you’ll have two layers of fabric and you’ll need to put them Right Sides Together (RST), unless otherwise stated. This is because doing that, when sewn, seam allowances will stay hidden in the inside of the garment, not showing on the outside.
Let’s take a look to what the right and the wrong sides of the fabric really are:
As you can see, the right side of the fabric is the “good side“, the one you’ll show on the outside of your garment, while the inside is the surface hidden near to the skin (or whatever you have under your clothes).
Not every fabric has such a dramatic difference between the right and the wrong side: I’ve chosen a printed one just because you need to see the difference, but there are woven fabrics that actually don’t have a right and wrong side (usually they are high-level wools, like the one I used for my Colorblocked Wool Top here).
Often you can recognize right and wrong sides only looking at the selvages: the right one is where the tiny holes are peaking up… This is because during production the fabric is moved inside machines right side up by little pins skewered in the selvages: the side where the fabric looks pushed through is then the wrong side.
A seam allowance(S.A.) is that slice of fabric that stays between the cut raw edge and the seam itself.
It’s width (in american patterns) is usually decided by the designer and included in the pattern (while here in Europe it’s usually determined by the sewist, since patterns are usually given without seam allowances).
A commonly used S.A. width is 5/8″ (1.5 cm) on woven and 3/8″ (1 cm) on knits, but always look for designer’s directions (or ask him/her if you’re unsure):
I have to admit that, being taught to add seam allowances, I’ve never been precise with their width: mum taught me making tailor’s tucks ALL AROUND the sewing pattern, right along the sewing line, then baste together pattern pieces. It was killing me all that hand-sewing!
Boring to the nth degree!
When I approached the PDF pattern world, I’ve learnt that having sewing allowances included was a huge time-saver for the sewer: no more tailor’s tucks, no more basting: just cut and sew:
But you absolutely be sure that you’re perfectly keeping seam allowances even from start to end of the project or you can end up with a too big (or too snug) garment (you know, you add 1/8″ here and there…)!
Now that you know the basic of a seam, we can go one step further and learn a couple of juicy trics:
Perfect seam allowances
As we have seen, you need to respect seam allowances width and there’s a simple trick for doing that: marking seam allowances on your sewing machine plate! Most sewing machines have lines engraved on top of their throat plate (see third pic), on the right of the needle.
If you don’t have them, or you’re not sure of which one to follow, measure the distance between your needle and where your fabric’s edge needs to be (in the example is a classic 5/8″ or 1 cm), and mark it down using either Post-it notes, a rubber band or even painter’s paper tape.
You’ll only need to line up your fabric’s raw edge to it and you’ll never be tempted again to look at the needle while sewing (huge beginner’s mistake!)
Two ways to start and stop a seam
This basically means that you need to start a couple of stitches inside the raw edge and start sewing in reverse mode (to the back – there should be a button or lever somewhere in your sewing machine that makes her go back! you can see mine here, it’s the second point).
Act the same when you reach the other end of the seam. Ta-dah! Seam’s heads secured!
Leave long tails, pull them both on one side of the fabric (obviously to the wrong side, if you’re topstitching), knot them together and cut tails. This way to fix seam’s ends is perfect for darts and pintucks (that will see later in a dedicated post).
What to do after sewing a seam?
No matter what kind of seam you’re doing, the first thing I’d suggest you to do (and the only one I would never skip) is pressing! Depending on the kind of seam and the result you want you’ll have to decide how to press your seam (open or to one side).