Never spend a small fortune on gazing balls again. And this one is not likely to break because a squirrel jumps on it.
Ok, here ya go.
Foam or a bowl to hold ball while working
Silicone ll sealant
Buckets (one for grout mix and one for clean water)
Place the bowling ball in a bowl, or what I do, is set it on a piece of waffled foam padding. This is to stabilize it so you can glue the mirror on it. I also fill the finger holes with liquid nails or silicone glue to even out the surface.
Using clear silicone II sealant, start gluing the mirror to the ball. I do it like working a jig saw puzzle, trying to keep a minimum of a ¼ inch space between the pieces. Cover the entire ball, except where it is resting on the bowl or support. Let it dry for several hours (overnight works best). Then carefully rotate the ball to finish gluing the mirror. Let the glue dry for a day or two. This is dependent on weather. Temperature is a factor in the glue drying well.