Doing Dishes Yields Science?

Washing up our tea pot, I managed to make a concave bubble in the top of the pot. It was amazing so I thought I would share it here.

The bubble remained until I popped it. I assume it was concave due to gravity. The hole is about three inches across. It's not very big but large enough to have a bubble instead of a straight film. I tried to recreate it but was unsuccessful, so I guess it wasn't really science, or at least not verifiable.