Most artists use paint, clay, and other common materials. Todd Johnson uses acrylic, lead, and a particle accelerator.
He describe the process on his site:
These pieces are created with the help of a particle accelerator. The accelerator produces up to five million volts and is used to accelerate a beam of electrons. The electrons are fired at pieces of acrylic plastic and penetrate deep within the slabs, resulting in a pool of electrons trapped under tremendous electrical potential.
The trapped charge is then carefully released by applying mechanical shock with a sharp insulated tool, and the electrons escape with a bright flash and loud pop. As the charges leave the plastic, they gather into channels following fractal branching rules just like river deltas, plants, and capillaries.
Controlling the energy and placement of the beam determines the final shape and character of the resulting figure.
Watch the video above to see it in action and then hit up the link below to see examples of the beautiful finished products.