These little cards are A7 size - the sort of size you see in wedding invitations. They are the perfect size for these small panels, measuring 2cm x 2cm.
For these designs, I laid out a long length of rainbow strands on the background clay, rolled them lightly to incorporate them into the background (which distorts the lines slightly), and then cut out three squares to create these panels.
I created a similar effect in the cards on the left using thin slices taken from the thicker rainbow strands. I placed the tiny circles randomly on black clay, rolled them in, and then cut out the panels. I think they look like streams of tiny rainbow bubbles.