I did some investigation of the effect. I can see no corona discharge
where I would expect it when I pull the electrodes off in a darkroom.
I did not dark adapt for this observation, and I'm 65, so probably
10 dB more sensitivity is available, more for younger eyes. I do hear
sparking, but I hear it when nothing is being pulled as well, and
besides I expect corona to be silent.
In a plane parallel geometry (two cookie sheets** and a 3 mm thick
piece of float plate glass with three cm clearance all 'round) I get
clear indication of residual charge on the glass*, but not the
dramatic effect of the conventional apparatus. My setup clearly leaks
charge too fast, and what cleaning I could do improved it. I will
take the plate of glass home and wash it in my dishwasher tonight
and try again tomorrow after an afterwash around the edges with
ethanol.
I use a short piece of tinsel rain taped to one plate as an
electroscope. I can tell by its jerky motion that there is arcing
somewhere when I charge the big capacitor. If I discharge it
immediately after charging it I get a really fat spark, so when it
is clean it should be quite impressive.
Leigh
* It performed splendidly as a base for an electrophorus after being
charged.
** I tried aluminum foil, too. It is hard to pull off after charging
and it has unavoidable sharp corners. It really sucks down onto the
glass surface nicely as it is being charged.