Like our bubble pictures this is not really an illusion, but I am fascinated by natural shapes. It’s a picture of blades of ice, and what you see here is about three inches across. The colours come from taking the picture in polarised light, as the crystal blades were forming in a shallow dish of water in a freezer.
Want to try your own pictures? The preparations are not trivial, but there’s nothing a school science section couldn’t handle.