Great video, Wayne.
Eric: If you're starting with large, chunky glass, more spherical than slab-shaped, I think any tool you use will leave a white spot where you hit it. If you look closely at old chunks in windows or lamps, those hit-marks are often visible. I think you may just need to smack away until you get the general size you want.
Some folks use wet saws to blank out chunk glass. This may be harder with something that resembles a bowling ball, tho.
In stained glass work, slab glass is called "dalle de verre". Tools for chipping slabs into interesting shapes & faceting their edges are available from Blenko in Milton, WV. The modern hammer for working with dalles has a carbide-tipped edge, I believe.
The "anvil" can be made from a substantial hunk of T-bar or angle iron. Still, working with a sphere will require some inventiveness!
Have fun & please let us know how it goes. - Tod