In the responses I got yesterday there was some confusion about how I cut the triangles for the second Delft quilt. For the inner triangles the rectangles are 8 1/4″ x 2 1/4″ – half cut on the diagonal in one direction, half cut on the opposite.
When you lay the two sets of triangles from the same fabric on top of one another they have the 90° angle in the same place. However, as you can see, were you to lay the dark set on the light set the 90° angle is on the opposite corner.
Here is the first set of triangles cut and placed upon the centre square (5 1/2″ x 5 1/2″) – they’re ready to be sewn. I’ve tentatively laid out the squares as they will appear in the quilt top – once the first triangles are attached I won’t have a lot of freedom to move these blocks around because I want adjacent blocks to be offset 90° from each other – the triangles determine that arrangement. In this array, I’ve cut all the light triangles to go in one direction, all the dark in the other.

When I have these assembled and trimmed to 7″ I will add the second triangle to each block – using a dark triangle against a light one, and a light triangle against a dark one.
Here are the rectangles cut for the second set of triangles – 9 1/2″ x 2 1/4″ – I haven’t cut them yet because I figured I’d mix up the inner and outer triangles which are very similar in size; they won’t be cut until the inner triangles are all attached. I’ve laid the rectangles out with the light fabrics face down – both sets of fabrics will be cut the same on the cutting board but because the light rectangles are face down, the diagonal cut will be 90° offset from the diagonal on the darks.
I have to think about this carefully before making these cuts because the light/dark cuts have to be opposite to the light/dark cuts for the first triangles! I think this presentation is correct for making that cut.
Now it’s time to begin sewing. If I’m organized about it, I should be able to chain piece the rows by adding one triangle to each square, then the second, etc.