How Are Fractal Wood Burning Patterns produced by DC Electricity?

Question

Here are 3 typical videos of fractal wood burning: video 1, video 2 and video 3.

As can be seen in all the videos, the different Lichtenberg figures develop simultaneously from both the positive and negative electrodes as the electric current follows leader lines within the wood that represent the pathways of least resistance. However, due to the high resistance of the wood, it heats up and burns to form carbon, which is a good conductor, and which allows the burning to move outwards from the electrodes. Multiple burn paths quickly develop and simultaneously expand from each electrode to produce quite stunning and unique Lichtenberg figures.

Surely, with DC electric current (voltage in the 2000 volt range and high amps are used) consisting of the one-way movement of electrons, a single Lichtenberg figure should be expected to grow from negative electrode and expand towards the positive electrode. So, exactly why do Lichtenberg figures develop simultaneously from each electrode if the burning is caused by electrons moving from the negative electrode to the positive electrode? (And, yes, the Lichtenberg figures are not true fractals)

David J

Answer 1

The effect of the battery is to create a potential difference between the anode and the cathode. Wood itself can be classified as a dielectric material, and becomes polarized in the presence of an external electric field.

In the examples you are watching the process of dielectric breakdown by what some call a disruptive device.

What causes the propagation patterns from both electrodes are polarized ions in the material of different charge (e.g. the ions are either positively or negatively charged depending on the charge of the electode).

Lightening is a great example, since it actually evolves both from the ground and the air as well.

At the molecular level there is a common model of how dielectric breakdown occurs. The breakdown voltage plays an important part in the operation of diodes and other semiconductor devices such as transistors.

So to recap, the battery creates an electric field which creates ions of different charge at opposite electodes. The potential causes the ions to propogate to the oppositely charged electrode creating the burn patterns from each electrode as the wood undergoes dielectric breakdown.

Update: Since the OP asked below, I wanted to highlight my response:

the only other item that I would add at the moment is that it is likely the conversion of the wood to charcoal that allows for the propagation of the lines. I found a rather interesting discussion of Electrically Conductive Charcoal that is prepared from biomass that might help. As far as which node and the effects of charge, if the wood is charge neutral initially it's indifferent to the polarity of the potential, it's the potential that matters to drive the process

The last point is that propagation isn't intelligent, it just knows that a potential exists, so it is neutral in opinion as to which electrode the path is forged from.