I had a request for more info on this process. I did not purchase a pattern for this. I saw it on a blog and asked if I could use the idea. (a long time ago!) You could use this method with t-shirts or regular fabric. Contrast is very important to maintain the 'shadow'. The shadow should be dark and the background/sashing should be much lighter. The recipent of this quilt requested no white as there were pets in the house.
You can use all the same size blocks or set them like a puzzle as I did. I did all the blocks first and then laid them out on my design wall till I had a setting I was happy with.
Here is the block make up
each center has two borders. A square of background (the small one) and a strip of the 'shadow'. Your strip can be as long or as wide as the block_ the WIDTH of the shadow needs to be uniform. You can see from the picture that all the blocks in this quilt are different. I cut the small background squares the same and sewed them on strip of the shadow. I sewd one side of shadow, trimmed it and then sewed on the other side of the shadow.
Let me know if you need a step by step mock up of this block.
Beth in AZ