What you want to do may be illegal in your country:
A spark radiates energy throughout the electromagnetic spectrum.
Nowadays, this is usually regarded as illegal radio frequency
interference and is suppressed, but in the early days of radio
communications (1880–1920), this was the means by which radio signals
were transmitted, in the unmodulated spark-gap transmitter. Many radio
spark gaps include cooling devices, such as the rotary gap and heat
sinks, since the spark gap becomes quite hot under continuous use at
high power.
As stated on Wikipedia
Assuming you are allowed to do that in your country, you only need to make sure the voltage between your metal parts is small enough for your voltage source. A spark is generated when you reach the air's breakdown voltage, which is, in normal condition, around 3'600'000 V/m. So for a 360V voltage source, you would need a distance <=0.1mm for the transfer to occur automatically. The arc are caused by the air reaching breakdown voltage causing ionization and current to flow. The current flow converts the air into ozone and other nasty stuffs. The color that one sees comes from the gazes which start to fluoresce. The mauve color typically comes from nitrogen and blue from oxygen. The current flow causes a depression which makes a little sound wave causing the "thunder" sound.
You either need a larger voltage source (dangerous), or something that will trigger your spark only at will (a mechanical switch rated to such a large voltage ?) A better solution would be a flyback converter. Basically, what you are trying to do is similar to a Tesla coil, so search for that kind of stuff.
Disclaimer: this is really dangerous. This is a bad idea. This may not be legal. This may not harm yourself, but it may harm someone else around you if the impulse is too strong.
If you decide to go on, try to put you circuit inside a Faraday cage to reduce EMI to a reasonable level.
