How to Avoid a Bias Disaster

Inside: Half-square and quarter-square triangles explained.

I was quilting a customer’s quilt recently, and all the edges were on the bias. All of them. How does this happen? Was it on purpose?

In this post you’ll learn when to use a half-square triangle, and when to use a quarter-square triangle. This will help you if you run into a pattern that is written incorrectly, as my customer’s quilt pattern must have been.

This is a half-square triangle. It is cut once across the diagonal.

Half-square triangles

This is a quarter-square triangle. It is cut twice across both diagonals.

Quarter-square triangles in quilting

In deciding which one to use, it is all about the grain. A half-square triangle has the straight grain on both short sides, and the bias on the long side. A quarter-square triangle has the straight grain on the long side, and the bias on both short sides. Whether making a single block or finishing a quilt, you want the straight grain on the outside.

For instance, in this block, you would use 4 half-square triangles, cut from 2 squares. This puts the straight grain on the outside of the block.

Half-square triangles in block

In this block, you would use 2 quarter-square triangles (for the brown fabric). Again, this puts the straight grain on the outside of the block. (The colored pieces would be half-square triangles.

Quarter-square triangles in block

Are you beginning to see how it works? You often see both of these kinds of triangles when setting a quilt on-point. You need both kinds of triangles when doing the setting. The half-squares triangles are on each corner of the quilt, and the quarter-square triangles are on the sides of the quilt. Now you have a straight grain all around the quilt top.

Setting triangles in a quilt

I posted a setting and corner triangle chart that is helpful in setting quilts on point, and also a chart of the diagonal sizes of quilt blocks. And, just for funsies, here’s an on-point quilt of mine, Pastelmania.

Pastelmania quilt

Pastelmania from Quilt Batik! ©2012 Cheryl Brown/That Patchwork Place. Photo by Brent Kane.

You don’t have to have bias edges on your quilts! Now you know how to avoid it.

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