Pencil cores contain no lead. They are mainly a mixture of graphite and clay. As a pencil moves across paper, the paper's microscopic texture removes graphite particles from the core, while graphite's layered structure lets flakes separate readily. The particles remain on and just within the paper fibres, held by relatively weak molecular attractions, and form the grey-black mark.
An eraser does not dissolve the graphite. When rubber or vinyl moves across the page, friction brings it into close contact with the mark, and the graphite is attracted more strongly to the eraser than to the paper. The particles transfer from the fibres to the eraser. An ordinary eraser also sheds crumbs as it rubs: the graphite-laden surface breaks away, exposing fresh material that can continue collecting particles. The grey crumbs on the desk contain both eraser material and removed graphite.
This is why a lightly written mark is easier to remove than one made with heavy pressure. Pressure pushes graphite further among the fibres and impresses a groove into the sheet. An eraser can remove much of the colour, but it cannot fully restore compressed paper. Excessive rubbing may also roughen or tear the surface.
Ink is usually harder to erase because a liquid can penetrate the fibre network and its dyes or pigments may be held more deeply. Pencil writing is correctable not because the mark is unreal, but because it is largely a layer of particles that can still be transferred.
Justin Caram explains the chemistry behind erasers in Popular Science magazine
Discover more from Geoffrey Chen
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