The Lily Pad: The Journal of White Lotus Quilting

The Mighty Half-Square Triangle

Next to the superhero square, the half-square triangle is probably the most important sub-atomic unit in quilting.  The half-square triangle appears in all sorts of patterns in lots of combinations, so it’s worth getting to be friends with.  In the Behemoth block, it appears in the Friendship Star, which is the second to last part of block #1.  So I feel compelled to try to explain it a bit even though it is a huge hairy topic in quilting, which invokes emotionally charged responses like in discussions of politics or religion.  And a little like religion, everyone is pretty much sure their way of making these little units is the best way.
Making the friendship star

Here are the beauties I sewed for the Friendship Star.  So let’s start with these as an example of the half-square triangle unit.   A half-square triangle is the triangle that happens when a square is divided along its diagonal.  That means that if you cut a triangle like this out of fabric, the long diagonal edge is on the bias.  And bias means STRETCH.  Fabric has the most give (distortion) along the bias.  So if you cut the triangles and sew them back together to make a two-triangle square (don’t worry, here’s where some of the confusion lies — this compound unit is ALSO called a half-square triangle, or HST), the piece will distort as you sew.  If you’ve starched the heck out of it, it might distort only a little.  But if your feed dogs are a little aggressive and the fabric has a lot of give, you’ll wind up with a diamond or trapezoid instead of a square.  WAH.  In the past I’ve trimmed many of these oddly shaped little units down to their more accurate size, but that means you have to start with bigger triangles than the match tells you, to accommodate the accumulation of sewing mistakes.

So here’s one place where I substantially differ from Bonnie Hunter, the genuis behind I don’t cut triangles first, unless it just can’t be helped.  I always sew first, then cut later.  If you sew the diagonal seam while the weave of the fabric is intact, it stabilizes the bias and prevents a lot of the distortion that happens when you sew on bias edges.  The other thing is that although you can mark your own sewing lines, and cut the odd size strips that HST’s call for, I have come to prefer sewing on pre-marked lines on Thangles paper, on normal pre-cut (by me or fabric companies) strip sizes.  It helps me make the most of my limited piecing time.

Making the friendship star

This is where I started for my Friendship Star adventure — by layering two identical size strips over each other, light over dark, and pinning on Thangles paper of the appropriate size.  Then I sewed on the dotted lines, cut on the solids, and after pressing produced the half-square triangles seen above.  Actually in the view of the HSTs above (first picture in post) I haven’t yet removed the paper.  If you leave the paper in when you press, that also stabilizes the bias and prevents distortions from the ironing.

The Friendship Star is a nine-patch block, with five plain squares and four half-square triangles.  The plain squares are divided into four dark squares and one light square (in the center) in this case but you could reverse the color balance and make the star look dark in a light background.  Here it is as a light star in a light background:

Making the friendship star

For a survey of half-square triangle construction methods, try this link: half-square triangle goodies.  Yum!  Lots of great stuff here.  There’s even triangle paper you can print out on your printer if you like that sort of thing!

After the Friendship Star, the only thing left in our Behemoth block #1 is two giant quarter-square triangles, which I’ll tackle in the next post.  And of course I’ll post a photo of the finished block #1.

Say sew happy, all!


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