Using the bias of woven fabrics
Clothing is amazing when we stop to think about it. In the middle ages, someone spent hours weaving threads back and forth to carefully craft yards of fabric. Plus there was all the time taken to spin the fiber—and even to harvest it. People then decided they had enough extra time to make curtains, blankets, napkins, mattress covers, and rugs! Textiles were considered liquid assets in the middle ages, as good as money. They were passed on in wills, recorded as taxes, and gifted in dowries.
Woven fabric is composed of warp and weft threads. Warp threads run the length of the loom and are strong enough to be worked under tension. Weft threads are passed up and down through the warp (or through a warp shed) to bind the fabric together.
The grain line always follows the warp of the fabric. Conveniently, this can be identified by the selvedge edges, which also follow the warp of the fabric. Selvedges typically don’t unravel. Measuring from selvedge to selvedge yields the width of the fabric (modern fabric is typically 44/45”, 54”, and 58/60”).
The crosswise-grain follows the weft of the fabric. On modern cotton broadcloth, warp and weft threads are generally identical. On other fabrics, the crosswise grain is considered weaker than the grain.
The true bias is 45° from the grain. This cuts across both the grain and crosswise grain equally. When cut, this edge will distort quickly when handled. Caution should be used to keep a bias edge from stretching while one sews.
The garment bias is anything other than a 45° angle. An isosceles triangle is an example of a typical bias used in garment construction. Caution should still be used to guard against stretching the bias.
A gore is a triangle with two edges sewn into place, and one edge left free as part of a hem. As a triangle, at least one of the sides will be cut on the bias. A garment will tend to fall in folds and “flow” towards the bias edge of the gore. You can use this to your advantage to accent or diminish aspects of your body shape.
“Side flow” is applying a gore so the straight edge is stitched to the body panel. This keeps straight lines down the center of the body and visually creates more fullness toward the outside of the body. This can balance a natural fullness in the center.
“Center flow” is applying a gore so the bias edge is stitched to the body panel. This will smooth the fabric over the hips and draw the weight of the fabric toward the center