How to make a Lichtenberg wood burner

Having recently becoming intrigued by Lichtenberg wood burners and their ability to create detailed burn patterns in wood, Coen Smit discovered that they are relatively straightforward to build —  but not exactly safe unless the right precautions are taken.

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Lichtenberg wood burners can turn a plain piece of wood into an intricate piece of art, reminiscent of fine Chinese/Japanese paintings of trees, as well as fractal-like images. The heart of the machine is a transformer liberated from an old microwave oven. It can generate the necessary 2000–3000 volts required to start the burning process, so safety features are crucial.

Sourcing your transformer
Apparently, neon sign transformers are more forgiving and are able to create effects that are more delicate, but they aren’t as ubiquitous as the microwave version. Another option is using the transformer normally fitted to oil-burning heaters.

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The secret, of course, when playing with electricity lies in being ultra-cautious, so if you want to explore the world of Lichtenberg wood burning you should set up your equipment in such a way that you switch it on and off remotely at the power point, or a switch fixed to the burner’s housing. Never reposition either of the burner leads unless the power is off at the switch, and preferably the power point as well.

Wiring up the microwave transformer
Having sourced your microwave, remove the casing and you will clearly see the transformer sitting below the magnetron and to the side of the oven itself. Beside it there should be a capacitor connected by a heavy-duty wire to the high-voltage side of the transformer (the secondary coil). I made sure to follow expert advice on how to safely discharge a microwave capacitor before touching the transformer.  

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Adding a safety switch
Taking a leaf from a YouTube video on making use of these transformers for this purpose, I purchased a double-pole, double-throw switch. When this sort of switch is in the ‘off’ position, both the active and neutral are disconnected. I purchased a 240-volt light baton with a small-wattage bulb to put in the circuit on the 240-volt side, as well as a red pilot warning light to fit between the switch and the transformer. The light before the switch warns me that there is 240-volt power going to the unit, while the red pilot light, when it comes on, tells me that the transformer is ready to be activated.
I also fitted two 16-amp, 250-volt bell press switches at either end of the box and wired them in on the supply side of the primary coil of the transformer. They are spaced more than a hand’s width apart and are wired in such a way that both must be held down for the transformer to be activated. It’s a simple and effective way to ensure that I don’t accidentally contact a live probe.

Parts housing
I sourced a strong Bakelite box salvaged from the electrics of a 6-metre refrigerated container to house the various bits and pieces. In it I inserted a tight-fitting, rigid plastic base plate to bolt the transformer to. This means that its mounting bolts are completely insulated and cannot possibly short to anything the unit happens to rest on.

Choosing the probes
I next turned my attention to manufacturing the two probes that transmit the current to the wood — the business end of the burner.  I settled on buying a couple of heavy-duty, jumper-lead alligator clips that can purportedly handle 600 amps. Their size makes them fairly stable when positioning on the timber with a short copper rod clamped in their jaws. They will also enable me to experiment with different metal sections in contact with the timber to create different burn effects. Despite their high 600-amp rating, I would strongly advise that you do NOT attempt to touch or move a probe while the burner is on. (They are designed for 12- and 24-volt systems, not 2000 -3000 volt ones.)

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How to burn
Once you are set up with wood, probes in place, and borax solution applied, doing a burn is a three-stage process. Turn on the mains power source, the double-throw switch, and press and hold both bell press switches, and the burn commences. To instantly stop the burn, just let go of one, or both, bell press switches.
I experimented with some scrap pieces of timber and varied the duration of the burns as well as the level of borax saturation. Using celery pine resulted in more finely detailed burns clearly showing the small spidery tendrils as the electricity made its way between the probes. Tasmanian oak burnt more deeply and rapidly, and lacked the fine detail of the celery pine. Tasmanian myrtle gave a similar result to the celery pine, and plywood gave a more coarse finish, but not as aggressive as the Tasmanian oak.

Apart from controlling the position of the two probes, the process of the burn itself is unpredictable, making every project unique and different. It therefore lends itself to adding further points of interest to bespoke items. such as wooden furniture, boxes, and the like.

This is a summary article; for further details such as construction costs and other safety considerations including how to build a fail-safe cut-out switch, read the full article in issue 80 of The Shed. You can find out where to buy a copy here:

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The Shed is a bi-monthly magazine that features how-to articles by experts, interviews with people undertaking amazing projects, and peeks into their sheds. A great read for the DIY enthusiast and those with a few tools after a bit of advice and inspiration.