Just a note about WFC made from tubes. Mind the spacing AND the alignment. Capacitance goes up the closer the electrodes are to each other. This particularly includes tubes in water where the inner tube is out of alignment and may be closer to one side of the inside of the outer tube than the other. You can see your capacitance with water as dielectric as much as triple if you do not have correct alignment. They should be centered as much as possible. It is best to measure the capacitance of each tube pair individually and make adjustments to your alignment as needed. I drilled and tapped holes in my tubes and use nylon screws to adjust the centre point of the tubes.
TS
