A4 Poly-Pockets for Capacitor?

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

Original poster: "Jolyon Vater Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

I am thinking of making a primary capacitor using A4-size poly-pockets (these
are thin plastic sheet pouches used to keep documents in -usually with a row of
holes down one side for the spring-binder)for the dielectric and aluminium foil
for the capacitor plates.
 
My anticipated method involves zig-zagging each foil between every two
poly-pockets at rightangles to the other foil. 
 
I have measured the capacitance of a single poly pocket capacitor this is circa
1.5 nanofarads  with the dielectric sandwiched between two plates I am doubtful
about the dielectric strength however -perhaps several
capacitor "units" will have to be stacked in series to increase the voltage
rating.
 
The capacitor is to be DC-charged by a rectified ignition-coil setup (driven by
555 via electronic ignition) powered from 13.8VDC supply.
A value of 20 nanofarads would be desirable as I have found this is necessary
to produce 6 inch sparks with my TC- so far I have been using 2 litre
pop-bottle SWC's and these fail often- for this reason I switch on the power
for the minimum time I need to observe the effect and turn off again -the
purple corona that seethes around the outside of the bottles does not take long
to find a weak spot!
 
Pop-bottles are polyethylene terepthalate (PET) -what is the probable breakdown
potential for this and what is it likely to be for a polypocket- only I
underestand ignition coil produces voltage in region of 20-40KV.
 
The capacitance per bottle is 3-4nF against 1.5 nF for a polypocket- what about
cutting open a bottle and laying the PET flat and interweaving with foil as
described?
 
Does anyone know if the "poly pocket/zigzagged-foil-at rightangles" method of
capacitor construction has ever been used for a primary cap or is it a novel
idea? has anyone used similar "stationery" materials such as transparencies for
capacitors -if so, what are the best types?
 
Or is it difficult and just a recipe for failure?
 
I am also considering building an MMC and I understand the capacitors are
expensive -however would this this be better value for money?