A: Well, aside from architectural definitions--which won't be helpful since we're talking about a quilt, here--a cornerstone is that little blob of fabric that goes in borders and in sashing where two strips of fabric meet. Or don't really meet, because the cornerstone is there instead. Dur.
In this quilt, the cornerstone is the little square with the lightening bolt on it.
Q: Why do you use cornerstones?
A: 1. it looks cool, 2. sometimes fabric won't look nice butted up against itself, like the stripe in our example, 3. you don't have quite enough fabric (2" short is still 2" short).
Q: Enough with the Qs & As already. Show me how it's done!
- Measure the width of your unfinished quilt. (We'll call it the medallion to cut down on confusion.) Measure the height. Cut your border fabric strips. Mine were 2.5". Cut the strips to the exact width and height of your medallion. Pin and sew the width strips to your medallion.
- Cut 4 cornerstones, the same as the width of the border strips. (2.5" here.) Pin and sew them to the ends of your height border strips.
- Pin and sew the height border strips to the medallion, being careful to match up the cornerstone seams to the seams between the width strip and the medallion.
- Add another border if you like. Hey! You've got quilt!