I started with regular gazing balls you can get at any garden store. I got mine at Big Lots for $8.88 or some strange Big Lots price like that. They came with a stand too. Although I'm not using the stand for these. Mine on on concrete slabs I salvaged from a recent demolition.
Then I filled each of the gazing balls with spray insulation foam. I was afraid that the glass gazing ball would be too fragile to handle the mosaic tiles. One can of expansion foam filled two gazing balls. You can get this foam at a hardware store like Home Depot. It comes in an aresol spray can.
Then I lightly sanded the outside of the gazing ball so the mastick would stick to the gazing ball better.
I used mastick, the same material used to tile a ceramic tile floor, to tile the gazing balls. I used this because this is what I had on hand.
I then grouted them using regular grout.
Here they are: