insulation testing

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "PotLuck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi List,
Has anyone done home insulation testing? I'm primarily interested in whether a
material will "hold off" a certain voltage or not. I see on the net in
commercial testing such tests for power factor tests, power losses and
monitoring of currents in the uA area. These of course are important properties
of a material but may be a little too in-depth for home testing and the
properties I'm looking for. 
 
The voltages I'm interested in looking at are in the range of ~7.5Kv at 60Hz,
not in the RF range inherent in normal tesla coil operations.
 
Any suggestions as to an "apparatus" that can be made easily? I have various
NSTs, variacs and transformer oil at hand along with a scope and several
multimeters.
 
Simply using a two electrodes with the material in question placed between them
(not under oil) sometimes produced a purple haze or what appears to be a
corona. Allowing the test to run for several minutes with the corona didn't
appear to form any holes in the material, not by the naked eye anyway, and
there was no burning. I've looked at mylar, polypropylene and HDPE.
 
Mylar film (adhesive backed) from McMaster-Carr has a dielectric strength rated
at 7500 V/mil. with 4mils placed between the electrodes "corona" developed at
about 4000 volts but no damage to the mylar was apparent. Again this was not
under oil.
 
But what is it I'm looking for? Lack of corona? Corona can't be good.
 
I'm relatively new to the high voltage arena so and advice in this area would
be greatly appreciated since insulation is a big part of coiling.
 
Thanks in advance! :)
 
Rick W.
SLC