Recent developments . . . I fried one of the 20KV Chinese radio capacitors.
There was a flash, and the coil went dead. I checked the cap with a meter and
it's toast.

Turns out they're not polypropylene, as I first reported, but polystyrene. A
pair of the same caps in series work beautifully, but they don't give the
bright, noisy discharges the single cap did.

Tonight I hooked up my Leyden jar battery (14 Leyden jars, 500pF capacitance
each) and the coil works OK, not as well as with the radio caps. It is an eerie
sight though. The jars are made from polypropylene canisters with aluminum soda
cans inside (see http://www.instructables.com/id/Soda_Can_Leyden_Jar/. When the
NST fires up there are tiny but steady arcs between the outside coatings and
bluish coronas inside the plastic tops. Couple that with the glare of the static
spark gap and the discharge at the terminals, and it becomes quite a show.

PBT