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BIAS
BIAS
A grain of fabric refers to the direction of the threads in the fabric. Fabrics have three grains: lengthwise grain (parallel to the selvage edge), crosswise grain (perpendicular to the selvage edge), and bias grain (45-degree angle to the lengthwise or crosswise grain). Each grain behaves differently when fabric is cut or manipulated.
Cross grain binding has a little more flexibility. If your borders are cut on the straight of grain, cross grain binding is a good choice. It is probably the most common type of binding used as it is both easy to make and an economical use of fabric. Bias binding is binding that is cut at a 45 degree angle from the selvedge.
That is the bias. When you have a pattern that states "cut on bias" the pattern piece would be placed in a fastion that would be a "diagonal line against fabric grain". Pattern pieces cut in this fashion are sometimes more difficult to sew because when fabric is cut on the bias it gives the cut edge more of a stretch.
The way the fabric is woven gives it different properties in different directions. When you are cutting a pattern you want to get all the pieces on the same "grain", i.e. a piece that will be vertical on your body should not be cut diagonally on the peace of fabric (unless you cut all the pieces diagonally or on the bias). The grain of the fabric is the natural direction of the fabric. The selvage is the edge of the fabric. When you buy a piece of fabric from the roll, you get two cut edges that fray and two factory edges that look different from the rest of the fabric and don't fray. These edges are the selvage. If the grain of the fabric runs from selvage to selvage that means the natural direction of the fabric (that you should use to line up your pattern pieces) runs straight across the fabric from factory edge to factory edge.
Bias
a line going diagonally across the grain of fabric
Cross grain means running across the regular grain of a piece of wood.Cross grain or crosswise grain in fabrics means that the fabric grain has more stretch than lengthwise but less than bias.
The way the fabric is woven gives it different properties in different directions. When you are cutting a pattern you want to get all the pieces on the same "grain", i.e. a piece that will be vertical on your body should not be cut diagonally on the peace of fabric (unless you cut all the pieces diagonally or on the bias). The grain of the fabric is the natural direction of the fabric, usually up and down along the length of the fabric.
Looking closely at a square of fabric, you will see a thread that runs vertically and a thread that runs horizontally, this is galled the grain of the fabric. Bias cut fabric is fabric that is cut diagonally to the grain. In other words, if you cut off a corner and then cut another strip at the same diagonal, say 2 1/2 inches wide, you will have a bias cut fabric. this strip of fabric can then be folded taking both outer edges toward the center and then folded again in half. It can be used to finish anything from blankets, quilts garments etc. as it is very bendable and pliable because it stretches as a result of being cut on the bias.