After posting my improv Keychain quilt recently, I had several requests for a Greek Key block tutorial, so here goes!
Start with several strips of each of 2 fabrics. Consider the gray on the left the 'main' fabric, and the natural on the right the 'background' fabric. Strips can be a variety of lengths and widths at this point, and the widths can even be angled - in fact that's preferred if you want a wonky block. The main thing to remember is you want straight lines, so I'd suggest cutting these with your rotary cutter and a ruler. I was aiming for blocks around 7"-8", so I cut my strips between 3/4"" and 1 1/2" wide.
Cut a few pieces and lay out according to photo below. You'll cut 2 center squares (could also be rectangles), then some strips at least as long as the previous section. All the cutting can be very random, as you'll trim at every step along the way.
Begin sewing by piecing the 2 center pieces. Press as desired.
If needed, trim the edge where you are going to add the next fabric piece to create a clean straight line. It can be angled if you choose, it just needs to be straight. Then sew on a strip of the main fabric as shown below. Press and trim. This will be the routine every time you add on a strip: press and trim. I found that finger-pressing worked ok for a few strips, then I'd go press the whole bit before adding the next few strips, and on and on. As you trim, feel free to trim 'wonky' if that's the look you're after.
Now here's where it begins to get tricky and you'll need to pay close attention from here on out. If you look at the photo above, it seems like you'd want to add another main fabric strip on the right side to start the spiral. But, the top background strip needs to be added first, per the photo below.
Now add the next main fabric strip.
Lay out a few more strips before continuing. Can you see the spiral beginning to develop? Keep adding strips, always careful to look ahead to make sure the next turn is covered, pressed, and trimmed.
You can continue adding strips until your block reaches your desired size. I chose to 'finish' each block with a strip of my main fabric, but that's just personal preference.
Trim edges to straighten, either wonky or 'square'.
In case you missed it, here's the quilt I made with my Greek Key blocks.