On the bias; on the straight

on the bias

• in the diagonal direction of the cloth.

straight

• a part of something that is not curved or bent, especially a section of a racetrack.

Many years ago I took a night course in machine sewing. I had an inherited, electric Necchi that did single stitch, back-and-forth lines that were perfect for the novice. It was a power horse and required very little care except the occasional drop or two of oil and some removal of threads and bits of cloth.
In the beginning we had to learn some of the jargon that would be used throughout the class. There was the tailor's ham for ironing, pin cushions, darts, pleats, selvedge, gathering, interfacing, notions, and a whole host of others. But the two that always amused me were the straight and the bias. The straight is a cut of fabric that is either parallel to the fiber or perpendicular to the fiber. A perpendicular cut might be the one you make when you are hemming curtains. The parallel cut might be the one if you were going to hang ribbons instead of curtains.
But the bias is a diagonal cut. Bias-cut garments have a totally different flow and drape than anything cut on the straight grain, and have a slinky, clingy, almost liquid effect when worn. Sometimes a thin strip of bias-cut cloth may be added to the hem of a skirt so that it flaps, snaps, or waves when the person is dancing or twirling.
You remember twirling, right?
Bias cutting requires a special skill. Obviously, if you are using fabric that has been cut on the straight for use, there will be less bias cutting that would provide equal lengths. (I was never a fan of geometry and generally took the words of the experts as being the gospel truth).
I don't sew very much these days. I might pull out the machine to fix patch pockets on shirts and pants or to reinforce the neckline of my scrubs if they get frayed. But the straight and bias still remain curious terms to me. Bias is so much more exciting than the straight!