In oceanography, a tool called a Secchi disk is sometimes used to measure visibility into the ocean depths. It’s a circular disk with black and white quadrants that is lowered into the ocean until it is no longer visible. The distance it was lowered is then recorded–although of course there’s always that one scientist that claims to still be able to see it! The disk looks just like the circles in this quilt.
The rail fence quilt blocks are representative of the visible light spectrum—from red to violet.
The pattern was from one of M’liss Rae Hawley’s fat quarter quilting books—I think it’s this one, but since I checked it out from the library, I can’t say for sure!