How does India-rubber and ink-eraser erase pencil and ink marks?

When India-rubber erases pencil-marks on paper, or ink-eraser erases ink-marks on paper, or pumice-stone rubs out ink-stains on our skin, what happens is really the same thing in each case. It is the rubbing, or the friction, that actually rubs away the outer layers of the paper or the skin, and so removes everything that they may contain.

Soft India-rubber rubs away only the surface-layer of paper, but that is enough for pencil-marks, which only deposit a thin layer of carbon on the surface of the paper. A harder rubber – or knife-edge, which acts in exactly the same way – will rub off thicker layer of paper, and will remove ink-marks, being made by a liquid which penetrates much more deeply into paper. Pumice-stone is hardest of all. And when we rub our fingers with it, it removes ink-stains which are deeply absorbed by our outer skin, as India-rubber could never do.

Additional reading:
Natural rubber (Wikipedia)
Ink eraser (Wikipedia)
Pumice (Wikipedia)

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