The fractal-like patterns in this platter are technically called Lichtenberg figure, and are actually the same sort of pattern that lightning makes in the sky. It’s fun to watch, and fun to do (if you have a bit of mad-scientist in you).
How it Works (kinda)
Wood does not conduct electricity at all well, so just shocking wood doesn’t do the job. So I add a conductive solution (something wet) on the wood to carry the electricity.
The way I picture this working is that the solution conducts the electricity through the surface of the wood. The current heats things up, which starts to evaporate the fluid. Once the wood is just dry enough (in a tiny area), the electricity will jump a little arc and burn the wood there.
That burned spot now is mostly carbon, which conducts electricity reasonably well. So things move on to the next tiny spot. Those spots keep progressing into tracks. As this is a dynamic process, with things changing all the time (carbon tracks, water evaporating, etc) the electricity finds its “good paths” are always changing, which makes it branch out here and there. As that happens over and over, always changing, it makes the lightning or tree patterns.
If the solution doesn’t conduct well enough, nothing happens. If it conducts too well, the current is too strong and will find places to jump and arc which just burns unpleasant patterns. The arcing can also happen if a section of the wood dries out and the current decides to jump that gap.
The process doesn’t happen “lightning-fast”. It can sometimes take several minutes of electricity flowing to start the process (but sometimes it starts up right away). And it can sometimes take a minute or so to get one of the traces like in the platter above.
A note about Safety
Electricity is dangerous. Seriously dangerous.
Most woodworkers know that a tablesaws and chainsaws are dangerous. Even if you don’t understand kickback or why a riving knife is a good thing, you can at least see some of the danger – a disk or chain containing dozens of sharp pointy bits, moving at very high speed.
Electricity is invisible. The danger is unseen. And most “normal” people don’t understand how electricity works at all. We turn on the switch and the light comes on.
High-voltage electricity is very dangerous (but just as invisible) and understood by even fewer people. Even those who work with electricity or electronics daily don’t generally understand the things that can happen at extreme voltages.
Electricity can kill you. Just a small current traveling through your body can shut down your heart. If you are lucky enough survive that, the current can burn you (internally and externally) and cause permanent cell damage to what doesn’t get burned. This is serious stuff.
One person I know ended up spending 6 weeks in the hospital enduring multiple surgeries, some amputations, and skin grafts. That doesn’t count physical therapy. She is lucky to be alive.
If you are going to attempt a project involving high-voltage electricity you need to take serious precautions. Like the way you might approach running a tablesaw or chainsaw in total darkness: you can’t see the danger, but it is still there and your safety precautions are the only thing that will keep you alive.
- be able to easily know when the power is on or off
- always assume it is on (your indicator light might have broken)
- have an easy way to turn things off (like a dead-man switch)
- wear good rubber-soled shoes
- keep one hand in a pocket (thus reducing the chance of electricity flowing between your arms and thru your heart)
- switch off, and unplug often
- always work as if the power is on
- keep your workarea clear and clean
- keep the excess water dried up and keep the wires out of any puddles
- never work alone
- must know how to contact emergency services (as should your work partner)
Did I mention that you should always assume the power is on.
Now that I’m sure you’re not going to try this on your own, we can get on with satisfying your curiosity about how I do it.
The Electrical Setup
To burn wood like this, it takes several thousand volts. I use either 7,500 or 15,000 because that’s what my transformer can do. But anything above a few thousand will work.
I use a neon sign transformer. These are designed to withstand being run at a mostly-short-circuit (which is what happens in a neon tube). Newer models may have safety things to shut the power off if arcing happens. While that’s probably a good thing for something that will hang in a restaurant window, it is not a helpful feature for my sort of usage.
I wired the 120v house-current side of my transformer with a switch, an indicator light, and a foot-switch. The double-switches give me good control over when it is on and when it isn’t. I set the foot switch well away from “the action” so if I need to move in, I have to step off the switch and it shuts things down.
The wire on the high-voltage side does not need to be too heavy. Although the voltage is high, the current is relatively low. If this wire is too stiff it will fight me as I am trying to position things on the workpiece. I think I am using something like 16 or 18 gauge. I put alligator clips on both ends of the wires, so I can reposition things easily.
I made a couple of wood blocks from old 2x4s and jabbed in a stiff solid wire (about a foot of 12 or 14 gauge). The 2×4 is just enough weight to keep it stable on the bench, and the stiff wire can be bent to any position. I set it in position so the tips of the wires touch the workpiece, and clip on the wires from the transformer.
The Wet Solution
The first thing that I tried was salt water. Seemed obvious. I have made this work, but I think the salt conducts too well, and I got a lot of arcing and unpleasant patterns. It is quite difficult to get just the right amount of salt to make things work well.
I have had most success with Baking Soda or Borax in water. The conductivity seems just about right, and the strength of the solution doesn’t seem to matter too much. I probably use about a tablespoon in a cup of water – but to be honest I just dump in a little and try it. I’ve done this enough that I can generally tell if it needs more or less.
The one downside to baking soda is that it can react with some woods. Some woodworkers even use baking soda to darken or “age” wood. Sometimes it is a nice effect. Sometimes not pronounced. But I’ve also given a walnut bowl a distinct greenish shade. Uck. So I always test on chunk of wood from the same batch, to see how it reacts. I have had some limited success with plain household Hydrogen Peroxide as a very mild bleach to lighten some of the staining from the baking soda solution.
Because of the reaction, I now mostly use Borax. It works just as well and has not reacted with any of the wood I’ve used it on. It does seem to be more sensitive to the concentration, so takes more tinkering sometimes to get it right.
Whatever solution I use, I apply it with a brush, sponge, towel, whatever. I want the wood damp or wet, but don’t want puddles. Sometimes it helps to apply some, let it soak in a bit, then apply more. As the burning progresses, some of the solution may dry up and cause arcing. If that happens, I just shut off the power and re-wet the dry spots.
The Clean Up
Once I’ve burned patterns in the wood, there’s a significant mess. The tracks are full of black soot, and my workpiece is wet.
So next, I scrub the traces with a brush and rinse under running water or in a tub of clear water. The traces will still be black, but if I don’t remove the soot, it will smear into the final finish.
Now everything needs to dry really well. I wipe off what water I can. Sometimes the piece goes back on the lathe and I use a paper towel to create friction. Or blow it dry with compressed air. Or just let it air dry.
When it has dried, the Lichtenberg patterns get a final pass with fine sandpaper and they will sharpen up a bit more.
Then I give the piece plenty of time (maybe several weeks) to completely air-dry before applying any finish. Since I know I’m going to make things wet in both the process and the cleanup, I know it will very likely warp and move. So I do all finish machining and sanding first, as I may not be able to do anything but hand-sanding once the process is done. Also, a good, smooth surface produces better patterns.
Different wood species burn differently – the grain does affect how the water solution is absorbed and the electricity sometimes follows the solution in the grain – sometimes not.
When things aren’t doing what I want, I simply turn off the switch. The power switch is the main control of the process.
If I don’t put solution somewhere, it won’t get burned there. This is the other control. If I do put solution somewhere, there is a chance of burning a pattern there (but no guarantee).
If things start arcing or burning where I don’t want, I turn it off and fuss with the solution – make it wetter or dryer in places to encourage the electricity to do something else.
Traces usually fan out from each of the contacts, and walk their way towards each other. Once the two traces touch, the process stops because there is now a good path of carbon for the electricity to follow (it will just continue to burn that path deeper).
I like to use something to keep the workpiece up off the surface of the bench (like a short slice of pvc pipe or a scrap of wood etc) so when the bench gets damp or wet, the workpiece isn’t sitting in it.
Microwave Oven Transformers
On the internet, I see a lot of people using (or attempting to use) the transformer from a microwave oven to do this.
I strongly recommend against using microwave oven transformers.
A microwave oven runs at around 1KW – that’s a lot of power. The secondary (high voltage side) of the transformer is around 2000 volts. It has no current-limiting ability built in – its intended use doesn’t require it. So it will pump out just as much current as it can, until it burns itself up or trips the circuit breaker.
This has two problems:
First, it is way too aggressive for burning wood. Too much current burns too fast and makes chunky fat traces without a lot of detail. That is my opinion.
Second, it is extremely dangerous. If you become part of the curent path, the transformer will pump high current through your body. If you do the math, you will find that the current on the 2000 volt side will probably exceed 1 amp before it blows the circuit breaker in your house. This is about 30 times what is required to cause heart fibrillation, and more than enough current to cause permanent damage (from both burns and cell damage). It can also freeze your muscles so you can’t let go or move to help yourself.
The person I know who was horribly injured by a microwave transformer said she just basically waited there, holding the wires, unable to move until the circuit breaker finally blew. Terrifying.
A Neon Sign Transformer usually produces higher voltages, but they output much lower currents – usually 30mA to 60mA. Additionally, they are current-limited by design.
The lower current, in my opinion, allows it to burn better patterns in wood. They are finer, with more detail, and less burning. A 30mA transformer is plenty to do the job.
However, it is still not “safe” by any means: 30mA is enough to trigger heart fibrillation, which is usually fatal without prompt help. It is probably not enough to cause severe burns or cell damage. However, electricity and the human body are pretty complex things, and there are no guarantees.
Lichtenberg Figure on Wikipedia – https://en.wikipedia.org/wiki/Lichtenberg_figure
My Demo for the Rocky Mountain Woodturners club – https://youtu.be/UP2OYGq7BJA
An episode of Tim Yoder’s show – https://youtu.be/b__z2apE7dA – (note there are two “underscore” (_) characters in there)
Google or YouTube searches to try:
- Lichtenberg Pyrography
- Fractal Wood Burning