Fractal wood burning

Craig Shearer - 11 September 2023

I might be behind the times (I usually am!) but this week, while doing some YouTube surfing, I came across a video on Fractal Wood Burning - specifically warning of the dangers of it. (And, of course, the YouTube algorithm, which I liken to a toddler, has now filled my page with other videos like it!)

So, what is fractal wood burning, or Lictenburg burning as it’s also known? Well it’s a technique where a high voltage is used to burn patterns into wood coated with some sort of electrolytic solution (to make it better conduct electricity).

Kids, adults, don’t try this at home!

There are many many videos and web pages all over social media on the internet that detail how to build a device for doing this from a transformer out of an old microwave oven.

Unfortunately, it seems that many people have been fascinated by the possibilities of producing some nice home-grown art.

So, to burn wood in this fashion, you need a source of high voltage electricity. And the way that this has been suggested is to salvage a transformer from an old microwave oven.

The microwaves are produced using a cavity magnetron. This is a vacuum tube device that produces the microwave energy, and it requires a high voltage to operate (as almost all valves or vacuum tubes do - though some valves were designed to work as low as 3V of High Tension (HT) voltage).

So, in a microwave oven, there’s a transformer that takes the normal mains voltage of 230V and steps it up to several thousand volts. Depending on the model, a magnetron might require 3 - 4kV.

When you pull a microwave oven apart (something I’ve admittedly never done) you will probably also encounter a capacitor, which may have some residual charge - at the high voltage - enough to give you a bad electric shock or even kill. So, there’s danger in that too.

But, there are projects online which describe using a microwave transformer to actually produce the high voltage necessary to produce the burning in wood. So, you have people plugging these contraptions in, and generating this high voltage and using electrodes, connected via car battery jumper leads, to burn the wood.

Over the past five years, 33 people have died from doing this, including a couple in the US.

There are a bunch of reasons this is incredibly dangerous. The transformer produces such high voltages that even attempts at insulating yourself may not work. If one side of the high voltage secondary winding of the transformer is connected to ground or earth, then even wearing rubber boots might not be enough insulation to prevent enough current travelling through you to electrocute you. And, using battery charger cables, which are rated for conducting high current, low voltage, is bad, as their insulation won’t be rated for the high voltages. And remember, it’s the current that kills, not the voltage. People have died from voltages as low as 42 volts! Though, as any elementary physics knowledge will tell you, it’s easier to cause higher currents to flow at higher voltages.

Even if you don’t die, if you manage to come in contact with the high voltage, people have been badly burned, resulting in loss of fingers.

The video that I watched goes on to point out that the normal safety devices fitted to modern homes - such as Residual Current Devices (RCDs) won’t save you. These are designed to detect an imbalance between the current flowing in the phase and neutral wires, indicating a leakage to ground. As the high voltage is on the other side of the transformer, the RCD can’t detect anything wrong. The transformer is doing its job of producing its high voltage. It can’t tell that it’s flowing through you, rather than the wood.

Anyway, I found this morbidly fascinating. The things that people will do, even if it can result in some pretty art.

The fascination has caused YouTube to take down videos that promote this, and the woodturners association in the US has banned any promotion of such projects.

Here ends your Public Safety Announcement!