Why do engineers avoid using pencils to mark metals?





Minerals interact electrically with each other, so that a series of reactions begin. 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 reactive materials 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 minerals. This means that its electrical reaction is very strong and a good energy source,. Lead is made in the ordinary pencil of graphite (a kind of carbon) and Chinese clay (silicate). The harder the pen the higher the proportion of graphite.

The avoidance of marking or writing in an active metal such as aluminum, which may be used in a non-greased manner on the wing of the aircraft, for example, may cause a firestorm due to carbon interaction with aluminum.





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 be automatically met by the expansion of the oxide layer) 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.