[artwhim]

Yes, as Eileen said you can make a sphere off the end of a mandrel. Depending on your design, it's not difficult.

It's a little more complicated to make a vortex or compression marble on a mandrel, but doable. Once you have your vortex or compression made, but still have it attached to the initial rod, garage it for a couple minutes while you add glass to the end of a dipped mandrel. Once you have enough glass on the end of the mandrel, attach the maria side of the marble. Flame cut the rod from the lens. Add whatever glass to the mandrel side that will round out the piece and finish the design. Then heat all well and round out the marble like normal. I'm sure there are other ways, but that's how I would accomplish it.