My little bird bath in the back yard was downright filthy and ugly. The picture shows dirt along the sides.
I originally tried scrubbing it out, even using a Magic Eraser, but to no avail. Then my brain kicked in and I realized that most of the filth was due to hard water scale. So I grabbed my ever-handy bottle of vinegar and filled the bird bath.
Thirty minutes later, after minimal scrubbing, the tiles are sparkly again. I filled it up with fresh cool water and am hoping for visitors soon.