Take new fabric directly to the washing machine to prepare it for sewing. Fabric is under a great deal of tension in the weaving process and will shrink as the threads return to their original length. Some weaves can shrink three inches per yard. The length of the fabric usually shrinks more than the width. Pre-washing the fabric with hot water and detergent not only shrinks the fabric, it removes the sizing. Sizing is starch like stuff that is needed to get thread through the loom. When it is removed the feel, the hand, of the fabric will often change. Plans for the fabric might change after washing. Sizing can cause skipped stitches, and prevent iron-on interfacing from bonding.
Wash the fabric alone, especially if it is dark colored, and look in the washer during the cycle. Hot water and detergent will remove more dye and sizing than cold water. Almost all dark fabrics bleed during the first wash. Black is very bad because often it is over dyed. Keep rewashing the fabric until the wash water is clear. Do not use fabric softener in the rinse cycle when preparing fabric.
Dry the fabric completely in the dryer. It is the dryer that causes most shrinkage. If the fabric is cotton or poly-cotton run it through the rinse cycle after it has been dried it once and dry it again. Do not use dryer softener sheets. They can keep the interfacing from bonding, use them after the garment is completed.
Shrink all of the items that are going to be part of the garment. The easy way to shrink trims is to put them in a leg cut from an old pair of panty hose. Tie a knot in the top and send them through the washer and dryer. If there is more than one piece of trim put them in separate legs to reduce tangling. Dark trims can also bleed so take care in combining items. To shrink bias binding or other cotton trims, remove the plastic wrap and wind some thread around the trim and cardboard. Place it, cardboard and all, in a glass dish. Cover with water, put in the microwave and cook until steaming. Then pour the water off, if there is dye in the water, repeat the process. After the excess dye is out, set the trim aside and let it air dry. Gently unwind the trim from the cardboard and press with lots of steam. Do not pull on the trim while pressing. Treat it gently so it is not stretched. Wind the trim on a toilet paper core to keep it from getting tangled. We have all seen trim that has shrunk once it was sewn on a garment and puckered the fabric. Have you ever seen trim that has stretched after it has been washed?
This is a lot of extra work, but shrinkage after the garment is completed can completely ruin hours of construction. Don't take short cuts. These special steps add polish to your sewing and prevent damage to the garment. Enjoy the creative process of sewing. Look for the best way to do things not the quickest. It is these techniques that will change your home made sewing into custom couture creations that will give you pleasure for a long time.
The last thing that must be shrunk is the interfacing. This applies to sew-in and iron-on interfacing. At one time I thought that I didn’t have to shrink interfacing. I was wrong. The yoke on one of my blouses is wrinkly because the interfacing shrank beneath the fabric. To shrink interfacing, lay it in gentle folds in the bath tub. Add just enough hot water to cover, and let it relax until the water cools. Roll the interfacing in a towel and gently blot dry. DO NOT twist or squeeze. Then lay the interfacing out on a table and let it dry completely. Gently roll the interfacing around an old wrapping paper core and put it away.
Thread is also under a lot of stress in the manufacture and in the sewing process. As the thread goes through the sewing machine it is pulled back and forth several times before it is sewn into the seam. The first thing that can be done to reduce the stress on thread is to use a longer stitch length. I tried to alter a dress where the sewer had used a stitch length of 0.5 mm. Those seams could not be taken apart and were puckered because of the short stitch length. Most sewing machines are pre set to a 2.5 mm stitch length, that is 10 to 12 stitches per inch. If that is raised to 3.5 mm or about 8 to 10 stitches per inch there will be less puckering and the sewing will go faster. No, it will not cause the seams to rip out. Seams should be be weaker than the fabric. If there is excess force in the area something is going to give. Should the seam hold and the fabric to tear? Or should the thread of the seam to pop and the fabric be OK? Seams can be re-sewn, mending ripped fabric is much harder.
Check that the upper and lower tensions are equal and loose enough for the project. Most of the newer machines do a good job of adjusting the tension but it never hurts to check. Take two 6 inch squares of the fabric you are going to be working on. Put one on top of the other and sew diagonally across, corner to corner. Take a firm hold on those corners and pull. If the top thread pops and the bottom holds the top tension is too tight. If the bottom thread pops and the top hold the top thread is too loose. It is always better to adjust the top tensions first because the bottom tension is factory set and harder to adjust. The threads should pop at the same time. Look at the sewing, if it looks puckered try a slightly longer stitch length.
Melding the seam also helps to prevent puckers. To 'meld' is to press the seam, preferably with steam, just the way that it went under the presser foot. This causes the thread to shrink and it embeds the thread into the fabric. Press both sides of a seam before it is pressed open or to the side. This takes a couple of seconds longer but the results are worth the effort.
Everything shrinks, but at different rates. The fabric, trims and interfacing are under a lot of stress and pull in the manufacturing process. Don’t take a chance on any part of a project. Even if it is not going to be used right away shrink it. When there is time to sew, don’t be stopped by untreated fabric or trims. When everything is prepared, place fabric, trims, pattern, buttons and thread together in a clear plastic bag. Then everything will be ready to sew when you are.