A snowball corner is when you sew through the diagonal of a square and flip one half of it over to form a triangle in the corner of a block or square. Below you can see a square ready to sew through the diagonal. Usually you draw a line to follow.
Use painter's tape (blue) as a guide to sew the diagonal line
You don't need to draw a line first, instead I stick a strip of painter's tape (or masking tape) to my sewing machine so the edge is right inline with my sewing line. By making sure the point/corner of the square stays inline with the tape I make a perfect seam. It saves drawing all those diagonal lines that most patterns call for.
Once the seam is sewn I press the inner point of the square over so all corners meet. It makes the perfect triangle. You can choose to trim the under triangles away leaving a quarter inch seam or leave them in tact.
Square with two snowball corners
If you trim them away you will end up with a pile of triangles like this...
Check out this blog post to discover an idea of what you can do with these: What to do with all those scraps!
Or if you sew a second line of stitching (before you trim) about 3/4" from the seam line within the corner section, then you can cut up the middle between the two stitched lines. This will create a half square triangle unit that you can use in another project.
How to make a spare half square triangle unit
Many blocks use half square triangle units. You can create a wonderful scrappy quilt if you collect these from many different projects. To find out more about half square triangles including how to trim them, check out this free lesson >>
