In daily life, we often use an eraser to remove pencil marks, but when we try to erase colored pen marks, we find that the effect is not satisfactory.

What scientific principles underlie this phenomenon? Why can an eraser easily erase pencil marks but not colored pen marks?

To answer these questions, we need to delve into the chemical and physical principles between erasers and different types of ink.

First, let's look at the process of erasing pencil marks with an eraser. Pencil marks are made of graphite particles left on the surface of paper, while an eraser is made of an elastic material. When we use an eraser to rub pencil marks, the surface of the eraser rubs against the surface of the paper, and the graphite particles adhere to the soft material of the eraser, lifting off the paper.

This process is similar to an "adhesion-peeling" process between the eraser and the paper, where the softness and elasticity of the eraser effectively remove the graphite particles from the paper surface.

However, colored pen marks are different from pencil marks. The ink commonly used in colored pens contains pigments and solvents, with pigments suspended in the solvent. When we use an eraser to rub colored pen marks, the softness and elasticity of the eraser cannot completely remove the pigments. Instead, the eraser can only remove a layer of pigment from the surface, leaving deeper layers of pigment on the paper.

This is because the adhesion between the pigments in colored pen ink and the paper surface is stronger than that of the graphite particles in pencil marks, and the eraser cannot effectively peel them off.

Additionally, the chemical composition of colored pen ink also affects the erasing effect of the eraser. Some colored pen inks contain special ingredients such as dyes or resins, which adhere more firmly to the paper surface and are not easily removed by the eraser. In contrast, the structure of graphite particles in pencils is relatively simple and easier to adhere to the soft material of the eraser.

In addition to chemical composition, the particle size of pigments in colored pen ink also affects the erasing effect of the eraser. Some pigments in colored pen ink have larger particle sizes, which the eraser cannot effectively remove, while others have smaller particle sizes and are easier to erase with the eraser. Therefore, the particle size of pigments in colored pen ink is also an important factor affecting the erasing effect of the eraser.

In summary, the main reasons why an eraser can erase pencil marks but not colored pen marks include: the stronger adhesion between the pigments in colored pen ink and the paper surface compared to the graphite particles in pencil marks; and the chemical composition and particle size of the pigments in colored pen ink also affect the erasing effect of the eraser. These factors together result in the poor erasing effect of the eraser on colored pen marks.