Minerals interact electrically with each other, so that a series of reactions begins. As in metals, some non-metallic materials have electrical properties and are involved in interactions. Carbon is one of these substances and falls into the list of reactants and is completely tin-plated. Not only that, but all metals lose electronics during these interactions and this is something in common, while carbon acquires electronics when it interacts with other metals. This means that its electrical reaction is very strong and a good energy source,. Lead is composed of ordinary graphite (a type of carbon) and Chinese clay (silicate). The harder the pen the higher the proportion of graphite.
Labeling or writing in an active metal such as aluminum, which may be unsaturated on the wing, for example, may cause a firestorm due to the carbon-aluminum interaction.
To avoid such a problem, the engineer must use a sharp signal tool, or a special dye that does not contain carbon. Because the sharp tool only scratches the surface of the metal (in the case of aluminum, the scratching will automatically adjust by extending the oxide layer on it) while the dye does not transfer the electrical reactions. Sometimes the engineer may have to cover the whole body of the aircraft with a protective coat, mark it, and then remove it after all the necessary places have been punctured.
