LICHTENBURG FIGURE

"Lichtenberg figures (German Lichtenberg-Figuren), or "Lichtenberg dust figures", are branching electric discharges that sometimes appear on the surface or in the interior of insulating materials. Lichtenberg figures are often associated with the progressive deterioration of high voltage components and equipment.  Lichtenberg figures are now known to occur on or within solids, liquids, and gases during electrical breakdown." Wikipedia