The coasters are travertine tiles that I found at Home Depot. Since they are a natural material, some of them are quite pitted or have broken corners or actual holes. I think it lends character to them, but wasn't sure how the children would react to the imperfections. They were not at all bothered. They stamped on the tiles using a permanent ink pad and also stamped a gift tag. We put little "feet" on the bottom with the type of craft foam that has a sticking backing.