Step 1: Obtain Neon Sign Transformer
Get a neon sign transformer rated for 9 - 12 kV and 30 mA. Make sure it's an old style, heavy coil transformer and not solid-state. The solid-state transformers won't start the arc.
I got a Transco 12 kV 30 mA transformer on Ebay for $35. It didn't have a wall plug, so I wired one on.
Step 2: Build a Base
Build a base from the something nonconductive and nonflammable. I chose wood, which doesn?t quite meet the nonflammable criteria. Drill two holes approximately 0.5 inches apart and shove two dowels in the holes. Use thick wire to make electrical connections between the output of the transformer and the dowels. Attach the base to the transformer to make the whole thing stable.
Step 3: Mount Copper Pipes
Mount two copper pipes on the dowels. Make the fit snug by putting the wire between the dowel and the pipe.
Connect the transformer output to the stiff wire.
Step 4: Set the Spacing
Set the spacing at the top of the copper pipes. I used a laser cut piece of acrylic. Something like drywall could also work. Eventually, the spark hung out under the acrylic long enough to ignite it. In later versions I put a gap between the two holes to allow the spark to pass through.
You have to experiment with the spacing; start around 2 inches and go as wide as you can.
Step 5: Build a Case
To make sure no one grabs the pipes, build a case around them.
I cut pieces of acrylic on a table saw and attached them to the base and a small frame at the top. There is a piece of reflective mylar on the back acrylic.
Step 6: Power Up and Take Pictures
Use a long exposure to take pictures.