Print it, repeatedly, without rotating and you get a secondary pattern of diagonal lines.
This rotation creates a radiating medallion.
Eva asked if the design of the stamp is South American. No, it's my own design, but certainly the kind of thing you often see in Inca or Mayan design, or even African textiles. I was reminded of the patterns I saw in the wonderful anthropology museum in Mexico City a couple years ago. I even remarked in that post that some of them would make great rubber stamps. Hmmm—I think I need to follow up on that idea.
Amy asked what I stamped with. Fabric paint.