Salt water capacitors
The salt water cap is the most basic of home build capacitors you can make (Dont be fooled in thinking they are not 100% leathal)
In its simplest form a capacitor is made of two conductive plates these are spaced apart by the "dielectric", the value of the capasitor is based on the thickness of the dielectric the dielecrtic value and the surface area of the conductor.

The dielectric value of glass is between 3.8 and 10 (depending on the type and qulity of the glass)

In the case of the sale water cap the glass of the bottle is the dielecrtic and the salt water on the outside and the salt water on the inside act as the conductors.
In out cap bank12 bottles are wired togetherwith a copper wire electrod down in to the center of the inner salt water, this is one side of the cap the other side of the cap is the water surounding all 12 bottles, this cap was rated at aprox 0.015uF and was good for 20KV+

All the salt water is topped off with cheap motor oil to surpress corona losses, also help to stop high voltage flash over.

You can calculate the value of your capacitor or just build it and "Suck it and see"

C = Capacitance in F (farads), convert F to uF (devide by 1,000,000)
A = Surface area of one plate
D = Dielectric value of glass = 3.8 to 10
d = thickness of dielectric 
Multple banks can be wired in series to increase the overall value of the capacitor. 
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