Lichtenberg Pyrography

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.

First, 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 blades moving at very high speed.

Electricity is invisible. The danger is unseen. And most “normal” people don’t understand how electricity works at all. 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.

You must:

  • 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.

If you do all that, I still can’t recommend that you try this. If you need more encouragement, check out what wikipedia has to say about electrocution or electric shock or electrical burns.

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. They can be found surplus from a sign shop, or on ebay, etc. 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 ga left over from a shop wiring project). 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 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 of soda in a cup of water – but to be honest I just dump some soda in a mason jar and shake it up. If there’s too much, the excess just settles to the bottom. Easy.

The one downside to baking soda is that it can react with some woods. Some woodworkers 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 green 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.

I have also recently started using Borax. It seems to work well at around a teaspoon or so per cup of water. And it has not reacted with any of the wood I’ve tried it on yet. 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. Also, 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. Some people use a spray bottle that can do a fine mist, but I find it easier to just hit it with my brush again (with the power off!).

If I want the baking soda “aging” effect, then once I am done burning I will re-wet the entire piece evenly, so the effect is uniform. Otherwise, I try to remove (rinse and dry) the solution soon as possible to minimize the reactions. Sometimes this means I will rinse and dry everything between burning each trace to minimize time of the soda on the wood.

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 damp or wet.

So next, I scrub the traces with a toothbrush and rinse under running water in a bucket or 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.

Other Notes

I practice and experiment with scrap wood often. I will try different wood species (the grain does affect how the water solution is absorbed and the electricity sometimes follows the solution in the grain – sometimes not). I like to experiment with various concentrations of solutions and various voltages. I am learning how to “encourage” certain patterns to happen.

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).

To prevent arcing around where the wire contacts the wood surface, I put a drop of solution around the contact point so it conducts better to the surface.

If things start arcing or burning where I don’t want, I turn it off and put a bit more solution on that place – it will start conducting thru the solution again rather than burning. Some people use a mister, but I just turn off the power and wipe it with my paint brush.

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.

The electricity is “concentrated” where the wires contact the wood – it all has to flow thru those points. Between the contacts, it “spreads out” (however wide I paint the solution). So most likely, the burn traces will start at or near each of the contacts. So it will usually make two “lightning bolts”, starting from each contact and spreading out towards the middle area. Sometimes, I want only one bolt “shooting down” from the top, or one tree “growing up” from the bottom. To do this, I “spread out” the electricity under the unwanted contact by placing a bit of paper towel or sponge under that contract and saturating it with solution. This seems to “de-concentrates” the current under that contact, and discourages a starting point there.

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 can not recommend that at all.  First, you need to have the technical skill to remove the thing from an old microwave and rewire it properly. But even then you are left with an unsatisfactory and less safe alternative to the neon sign transformer.

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 – the larger ones are up to 15000 volts. But they output much lower currents – usually either 30mA or 60mA (0.03 or 0.06 amps) on the secondary side. Additionally, the neon sign transformer is current-limited and designed to run indefinitely at that current in a short-circuit. That’s basically what it needs to do to power a neon sign tube, and is pretty close to what is needed when burning wood.

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

Wood Turning by Dave Landers