A Marx Generator is a spectacularly impressive electrical machine for storing up energy, and releasing it in brilliant bursts. Using only spark gap switches, capacitors, and either resistors or inductors, one can multiply an intermediate high voltage (say, 30 kV) by many times- the multiple depends on the number of capacitor stages built.
In 2012 I made a very simple marx generator which had 6 stages and a maximum theoretical output of 180kV. I used it to create images like these, of the veins of leaves conducting the arc through a leaf.
Recently I found a few additional Sprague 30kV 3600pF capacitors, and so decided to increase the number of stages in the system, and thus bump the maximum attainable voltage from 180kV to 240kV. It was also an opportunity to clean up the design with laser cut acrylic and better fluid resistors (the blue tubing is actually blue copper sulfate solution inside of clear tubing). These “Liquid Resistors” compare very favorably with the alternative, commercially sourced, high voltage resistors. Commercially available high voltage resistors are expensive, and there can be long lead times too. By contrast, I made this in an afternoon, for about $20 in materials (I had the acrylic and capacitors already). Plus, Liquid resistors are tunable- just change the electrolyte concentration!
The downside of liquid resistors is that periodically you must purge air bubbles, and scrupulously check for leaks before any use. (I’ve never found one, and let this system sit for over a year at a time). I have also noticed that after a year, the old cheap vinyl tubing (bought at home depot for about $3) appeared to have lead precipitation at spots due to reactions between the copper sulfate and the lead plasticizers in the tubing wall. However, because of the long path length of the tubing between each copper “tap” on the tubing helix, such localized presumably metallic deposits hardly perturb the nominal 10kOhm resistance between rungs.