Lichtenberg Burning - the Science

Here I attempt to explain to the curious how I think Lichtenberg Burning works, as I struggled to find these details myself.

I’ve focused on a flat wood surface, loaded appropriately with an electrolytic solution, and burned using high voltage (AC) to obtain a Lichtenberg figure. This is sometimes called fractal burning (which is wrong).

I’m not going to detail what you need to build your own setup, as you shouldn’t do it – I’ll leave that to the content creators that go strangely quiet after a while.

From everything I have looked at online, nothing has adequately addressed the safety aspect. Very few people are qualified to do this safely, and it appears none have explained to the masses how this could be done. There is a reason for this. Don’t do it.

The mechanism of how the burn is created is an interesting phenomena, but again, I’ve found nothing on this directly. Here is my interpretation

Electrical connections to the wood can be simple points, like a crocodile clip, or a screw or nail. These will promote tree initiation. Using a large contact area to the wood, such as electrolytic solution soaked sponge or similar, will reduce the chances of tree initiation at that terminal. The two terminals can be close together (0.2m), or far apart (2m), where the distance will affect the field strength and so change the tree shape, speed of burn, and probability of tree initiation. Less than 1m creates a seemingly reliable burn.

The insulating wood needs to have a conductive path across its surface. This path is provided by an electrically conductive solution – salt water. In water, salt breaks down (dissociates) into anions (and cations), which move like electrons when subjected to a voltage (electric potential). The electrolyte can be made of sodium bicarbonate mixed with warm water at about 90g per litre (so as to avoid any undissolved solids). Even sea water will work. The wood surface should be coated but not puddled. A fine spray application of electrolyte should be used where a burn is wanted. Burns are much less likely to occur on areas that are free of electrolyte. Electrolyte can be applied evenly to the surface, until the droplets begin to homogenise and almost form a shine.

Voltage can be applied once the solution has been partially absorbed into the surface (normally under 1 minute, but varying largely depending on environmental factors, and the wood itself). The AC current can flow using this electrolytic solution at the surface layer as the conductor.

The resistance of the conduction path causes heat (joule heating). Where connections are made to the wood using a point connection, the current density will be higher, causing increased localised heating. Therefore this is usually the first area where the solution dries out, causing a break in the electrolytic conductor. This is called dry banding.

Once the solution dries, there is a high voltage across the dry area, which may be a very small area. When this voltage is large enough to ionise the air, a conductive path is created through the air, close to the surface, and an arc can form. The arc across the surface will super heat the surroundings, causing the air to ionise, creating plasma, and the wood to burn causing carbonisation. The dry band is now shorted with conductive carbon from the burned wood, and the tiny arc is extinguished.

A further dry band can be formed by the heat from the nearby plasma, or by the current density in the electrolyte near the new carbon conductor being high, relative to the surrounding electrolyte. The initial arc is therefore likely to lead to another arc. Through this continuing process, a burn appears to grow from connection to connection at maybe 10s of millimetres per second. This is called treeing.

The arcs are often too small to see, even at 4kV will happen many times per 50Hz cycle – each time the potential across the dry band is enough to breakdown the air. The carbon conductor now carries the bulk of the current, and the heat generated in this conductor further burns the wood, creating a deeper burn.

The result is a Lichtenberg figure, which can have many details that can be understood, and be entirely unique.

The finer details of a burn are very superficial, and can be removed by even a moderate finishing grit. The larger burns that formed the conductor for a longer duration can be much deeper.

If the wood is not finished with a fine grit paper prior to the burn, the distribution of the electrolytic solution on a sub millimetre level can cause un-even drying, and the arcs will create a more furry burn pattern. For a finely finished surface, the arcs are more focused to the direction of the potential (at least on a millimetre scale).

On a connector point to point scale, the direction of the burn will be affected by many factors such as: wood type, wood density / porosity, air movement, connecting circuitry and cabling (magnetic fields), finish, electrolytic solution distribution, and obviously connector position. Sometimes this means initiation points occur at sites other than the terminals.

As like charges repel, the branching may occur when there is not a linear potential gradient. The variations in the wood and electrolyte will be non-uniform and vary as the process progresses, which will directly affect the conductors and magnetic fields creating more possibilities for branching.

An AC voltage is normally preferable for creating Lichtenberg burns, but a DC bias will affect the symmetry of the burn, with a positive bias causing more branches. The burn is still likely to initiate on both AC terminals, but the shapes of the Lichtenberg figures from each terminal will be different. A negative conductor will more readily create ionised air, due to electrons having a lower energy required to free them from the conductor than the positive ions, possibly allowing a more direct path to the positive terminal.

An AC voltage is less likely to form sustained arcs too, though large arcs are still possible. Even at 4kV, 150mm arcs through air are common, but usually not desired.

The process appears to work on most woods, but the results vary. Oak can be left with fine detailed burns, beach and ash can produce similar results, but each with unique characteristics. Whereas pines result in deeper burns with fewer, larger branches. Leather works, but the result is neither aesthetic to the eye or the nose. The electrolytic solution can also effect tannins in some wood, which can give an aged appearance.

Just for completeness, here are some burns including a 1.9m burn, colour, glow in the dark, stars, varnish finish, and oil finish.

Please get in touch if you can add to the understanding of the science.

(corrections and updates welcome)