You might be able to see a ring of copper tubing in the basin. This was put in to minimize algae growth in the birdbath. Sure enough, it’s easy to see that the granite within a few inches of the metal is clear of algae. There is some around toward the edges. A little trick that should make maintenance easier.
This birdbath was made by the owner’s father when he was a stonemason’s apprentice.
I love the floral touch for the tour. There were many of those all around the garden.