The iron is not only for the end of a sewing project. In garment sewing, the iron is actually part of the construction process. A seam you have just sewn may appear to stand up off the fabric, be a bit rippled, or look stiff and sharp. After it is pressed, the stitches lay more deeply into the fabric, and the seam starts to act like part of the garment, not just a line on top of it.
Pressing is not the back-and-forth motion you use to remove wrinkles from a shirt. It is usually the iron that is placed on a surface, held there for a few seconds, and lifted again, to avoid dragging the fabric and stretching it, especially around the bias, curves, hems, and facings. Its objective is to soften or shape the seam without moving the fabric out of its place. A pressing cloth will also protect the surface from iron shine, or help with difficult materials.
A nice time to press seams is after you finish sewing a seam, before you meet a new intersecting seam. First, flatten the seam in its original sewing direction. This sets the seam thread. Next, open the seam flat or press to one side depending on the pattern recommendation and garment placement. If you omit this step, the next seam will trap a crease or create a puffy corner and make the two pieces more difficult to match. Pressing early usually makes sewing later much easier.
Hems are also a really good example of pressing. With a pinned hem, the fabric will easily slip while it is sewn, especially on curved hems and delicate fabrics. When you measure the fold, press it down, re-fold, and then press it again, it becomes more stable, and it is simpler to sew because it is already sitting flat.
Darts also look better with careful pressing. After sewing the dart to the point, the fabric must be shaped so that the point is not crushed or a sharp bump appears on one side of it. It helps if you can push the dart in the direction that makes the garment hang best. Pressing a curved dart on a tailor’s ham can be done easily, but if you don’t have one, a small rolled up towel is all you need to help you learn how much steam and pressure are needed for that piece of fabric.
Always try to press on fabric scraps first, before pressing your real garment. Try the fabric temperature and steam and pressure settings. Some fabric will flatten very fast, others will mark easily and take the impression of your iron. Take note of the settings: hot or cool, steam or dry, with or without a pressing cloth, light pressure or heavy; all of this information will keep the garment from shiny spots, scorching or distortion later.
Pressing is one of those little steps that often make a garment better. If it looks badly after sewing, press before you consider the result a bad job. Let it settle, and after that, you will have a better result. Learning when to press gives the sewing process a steadier rhythm: stitch, press, check, then continue.