Stefan's Tesla-Pages

Some more photographs of my beautiful fulgurites


The original one made by lightning

The ones made by Toni and me (and also Daniel and Max)

The one I bought on EBAY:

a look into the tube:

from the side:

some views through the tube:


more views through the tube:


see how transparent it is:

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Homemade Fulgurites:

On Halloween 2005, my fellow coiler Toni and I made some Fulgurites using his BIG 10kV (at 50kVA!) xfmr. I found some information on how to do this on the website of GTL-member Stefan Binder ( and at the 4HV-forum (;action=display;threadid=4165).

So we connected two phases to 400V over a 7.25Ohm resistor (breaking resistor of a crane, thanks again to Stefan Bauer for donating this beast to me!). A measurement before with 230V applied to the high voltage side of the xfmr resulted in 6.9V on the low voltage side, so the transformation ratio is approx. 1:33.

We filled a flowerpot with silica sand. One electrode of the xfmr was burried at the bottom of the pot (screwed through the bottom hole) and we sticked a copper pipe (8mm diameter) into the pot before filling in the sand. The copper pipe can be pulled upwards with a lever mechanism while the arc is burning. We measured 28A on the low voltage side (arc current approx. 0.93A) at the beginning down to 20A (0.67A arc current) when the arc broke apart at the end of the pulling process. The slower you pull, the thicker the glass wall will be (=> more sturdy fulgurite). We started with a pulling time of approx. 1min for the first fulgurite up to 2-3mins for the third one.

We achieved 3 hollow fulgrites in the first three trials! Length was approx. 10cm (4") with an outer diameter at the lower end of 6-8mm and a wall thickness of 0.7-1mm. The bottom end was fatter (bigger diameter) because of the higher current at the beginning. After a certain length of arc (and fulgurite) was created, the resistance of the arc rised, reducing the current and therefore the arc diameter.  

Here you can see Toni at the lever mechanism, the flowerpot on the left at the floor and the big green xfmr behind the stairs on the left side:

This is the big resistor, we used a blower for cooling (resistor was rated for 12A at 40% duty ratio, not for the 28A cont. we pumped through it...), on top of the IKEA salad bowl is the ammeter:

Our first homemade fulgurites:

A view inside:

A closer look:

At first, I wanted to create fulgurites the original way with a pulse discharge. But lets see how much energy we needed to produce the ones (100mm x 4mm average diameter) seen above: we wasted some voltage in the resistor: dU=R*I = 7,25*25=181V, so the xfmr got only 212V at 25A for 120s, that's 636kJ! (Yes, I know this is not really the right way to calculate this, but it is sufficient for a rough calculation I think.) Compare this to the really big capacitor bank I plan together with Daniel and Toni at the moment which will have "only" 47kJ... With this capacitor bank, we perhaps can produce a 2cm long fulgurite of 2mm diameter (1/10 of the volume of molten silica sand of the 10cm-fulgurite pictured above). The geometry of this smaller fulgurite will be not so impressive but the process of creation will be for sure! Perhaps we can do this at one of the the Teslathons in 2006+x...

Plans for the next session:

On 6th August 2006 the Teslathon2006 organisation team (Toni, Daniel, Max and me) hold a workshop at Tonis house to discuss the last Teslathon. Toni couldn't attend the Teslathon2006, so we performed a small one the day after where we electrified the glass plate (34cm arcs around the edges).

We also drew some more fulgurites:

< more images coming soon >

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An interesting scientific paper on how to make a fulgurite using natural lightning:

And yes, we still have some good ideas how to make some more special things out of molten sand ;-)
(See my email 10.08.2006)

Some interesting links to fulgurites:

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